Technical BRAKES, The Brake Article to end all Brake Articles!

ABOUT BRAKES
By Denny Art
From Rod Action circa 1975

THE FOLLOWING story has been written to be the most comprehensive article ever printed on possible brake combinations that have been done on 1928-48 Ford axles. All the conversions are back-to-back and reading about them all is an excellent cross-reference for choosing the brake system most suited to your needs. If you want to adapt your own system, read the whole story to understand how basic and similar all the conversions are, especially the disc brakes. The knowledge of how basic is the procedure to adapt any brake will help you in adapting and machining a combination of your choice. Remember this most important thing: the true success to any brake changeover is accuracy, so engineer, measure, and machine with accuracy.

There are also a few items that are repeated in each brake story; they are of utmost importance and worth an explanation. One of these is the grade 8 bolt. This is a minimum hardness, but it is the easiest to find of the superbolts. The reason for such hard bolts is because of the high shear factor of the braking pressure perpendicular to the bolt shank. Bolts of a lesser hardness would shear upon emergency braking or repeated hard braking.

To distinguish a grade 8 bolt is not the easiest thing to do. There is a standard for grade markings on bolt heads. The problem is that, depending on the manufacturer and alloy used, a grade 8 bolt could be substandard to the S.A.E. ratings. Buy from a known company such as Rockford for quality-controlled bolts.

Some bolts are not marked on the head, even though they are grade 8, because they were made for a special application and ordered in large quantities. Some bolt heads have individual manufacturer markings, which mean they could be in the superbolt category. There is no S.A.E. marking standards above grade 8. The individual marks could also represent a bolt made special for a certain manufacturer of units that uses bolts.

Not all socket head capscrews (Allen bolts) are grade 8. If they are cadmium plated or stainless they are of aircraft quality and expensive. If they are black they could be either grade 8 or grade 1. You can only case harden mild steel, which means impregnating the exposed surface with carbon. This gives a double hard surface (for •a depth measured in thousandths of an inch), but under that is non-heat treatable low carbon steel. A grade 8 bolt is heat treated but you can cut it with a file. A case hardened bolt can only be ground and a file will slide over the bolt like it had no teeth. Take a file when you buy black Allen bolts. If a file won't cut the surface, it is a grade 1.

Torque the bolts for maximum strength and life. This is to avoid failure due to vibration or fatigue and to exceed the forces of separation of the two pieces bolted together during operation. Also use compatible nuts or tapped holes that will hold the torque of the bolt without stripping.

The machine set-up references are only to clarify set-up procedure. Some brackets will clear chuck jaws where others won't when turning inside or outside diameters. This is due to bracket size differences and other machine set-ups must be employed to compensate. Lathe chuck sizes also vary and, again, machine set-ups are according to chuck jaw sizes. By no means are the set-ups indicated meant to be the only ones that can be used. They are recommended for the amateur, but the professional can do it any way he prefers. Most questions can be answered by using a machinist manual or a machinist textbook available at a library or bookstore. Don't guess, it could cost you an expensive tool, the machine, your fingers, a hand, even your life.

All homemade - brackets are made from 1015 or 1018 hot rolled steel and surface ground. 1015 steel is nothing more than low carbon (mild) steel. Cold rolled steel, which has a smooth shiny surface, is pressed between rollers when it is cold to give its finish. The pressing makes the steel denser at the surface than the middle, which gives cold rolled a built-in surface tension on each side. To remove one surface will make the steel bow to the still-dense side, because of the surface tension. Hot rolled steel does not have this surface tension but it has a scaly surface. The reason for grinding it is to get the two surfaces on one piece of steel parallel and smooth. Hot rolled steel will not bow or warp when ground, and it is cheaper than cold rolled.

Sometimes at the factory, units are assembled from parts that aren't quite true until final machining. The machining makes an out of alignment unit correct but when the unit is disassembled, the pieces are out of alignment in relation to themselves. Brake drums and rotors are such units. Always machine or grind all mating surfaces for accuracy before assembly.

When measuring the caliper/rotor difference to adjust for equal clearance on each side, divide the offset in half, This means that if you have .020-inch more clearance on one side than the other, only use a .010-inch shim. If you add a .020-inch shim it would offset the difference .020-inch in the opposite direction. In other words, split the surplus in half, and give each side an equal amount to keep the sides equal. If you took the total surplus from the heavy side and put it on the light side, you would have the same imbalance, only on the opposite side.

 

Brakes For Early Ford Spindles

Ever since Fords started rolling off the assembly line, somebody has been trying to make them go faster. It didn't take long to realize that the panic binders didn't give the necessary Whoa to the new go. All types of brakes have been developed with some success and sold as accessory units to the public.

With the advent of the Model A came the four-wheel mechanical brake system. They had to go four-wheel brakes because of increased weight and performance. Cars kept getting heavier and faster, but the factory brakes stayed essentially the same until 1939, when Ford added a hydraulic wheel cylinder to increase the pressure of the shoes against the drum. These brakes were the dual anchor Lockheed type used from 1939 to 1948.

Hydraulic brakes are much more efficient than mechanical units, so the guys running Ford mechanicals switched to hydraulics. On '37 and '38 models it's just a matter of bolting both the front and rear assemblies on, including backing plates, shoes, wheel cylinders, and hubs.

With '28 through '34 Fords, the plot thickens. First we need to buy a hydraulic conversion kit that consists of two steel rings, two smaller adapter rings that slide over the spindle bolts and two cone-shaped shims. When the mechanical linkage is removed two sockets remain on the tops of the king-pins and serve no useful purpose. Saw them off if you wish. The two large ring spacers are slid over the "A" spindle backing plate registers. They are just the thickness of the backing plates and 3/16-inch wide to make up the difference between the center hole diameter of "A" backing plates and '39 or later backing plates. With the backing plates in position, note that the bolt-up holes in the hydraulic plates are spaced slightly wider than the 'A" spindle holes. A small rattail file alleviates this problem. Position the grease baffle and bolt everything up. The baffle keeps the spacer ring in place. Next, place the "A" grease seal ring on the spindle. The new ring is used to space the new hub bearing for correct drum clearance and for the new drum grease seals.

On an "A" rear end, a cone-shaped spacer is required on each tapered axle end to space the drum the right distance from the backing plate. The backing plates will bolt right up to the rear axle housings after clearance work has been done. First, the Houdaille type shock mount/spring hanger on the rear end will hit the backing plate. The area in question is just over one inch wide, a half-inch tall and just below the wheel cylinder. Cut a notch in the backing plate at this point for clearance and everything is kosher. The brake line might interfere here, so if you are not going to use the stock shock links, cut them off. If they are to be retained, file a depression in the top of the spring hanger (to the back side of the shock mount) for the brake line to snuggle into. Now bolt everything together. 1932-34 cars don't have backing plate clearance problems but they still use the rear axle shims and spindle spacers.

1941-48 Lincoln Bendix brakes are much better than Ford Lockheed brakes. They are of the duo-servo layout and have a higher brake factor; this means more braking for less pedal pressure and more consistent fade characteristics under rough conditions. They are recommended for use on the front spindles only for better braking on '32-'48 cars using '39-'48 Ford Lockheed brakes. Lincolns at both front and rear have been used in some instances with good results.

In our research we found that Lincoln front backing plates only fit '32-'34 spindles. A notch must be cut below the wheel cylinder to clear the kingpin bearing on top of the spindle. Because the '37-'48 Ford and '41-48 Lincoln brake drums are of the same dimension, each can be used on the front with the 'A" spindle spacer. Lincoln backing plates on the rear must be clearanced the same as Ford on the 'A" rear end. The best way to use Lincoln brakes on the front is to use '37-'48 Ford spindles with the Lincoln rear end backing plates which bolt on with no alterations. Use either Lincoln or Ford hydraulic brake drums with no spacer. Lincoln brakes are scarce and expensive because they rate with the best.

With the advent of the first overhead V8, the advanced machining and engineering techniques attributed to the effect of WWII, and the need of a good passenger car brake, came a boom of differently engineered brakes. With a little experimenting and imagination some of these brakes were adapted to early Ford spindles. In our research we found that '52 Ford pickup brakes will fit '37-48 spindles with a change of bearings, races, and seals. Finned aluminum Buick drums of the late '50s and early '60s can also be adapted to the pickup brake. We also found '51 or earlier Studebaker Champion front brakes on a Model A front axle.

Probably the most popular front brake swap on early Ford spindles in the late '50s and early '60s was the finned aluminum Buick drum and the Chrysler total contact brake. The Buick drum was of the type used during the '59 through '62 period. The Chrysler brake was of the type introduced around '59.

The Chrysler total brake assembly required no modification. To provide a seat and to locate the Chrysler support plate, machine the face of the Ford spindle to the diameter of the backing plate hole, a depth of 1/16-inch. Another way is like that of the Ford hydraulic to 'A" spindle adapter. Fabricate an aluminum spacer ring 1/4-inch thick to fit between the locating shoulder on the spindle and the hole diameter of the backing plate.

The brake support plate is separate from the dust shield, which looks like a backing plate. The dust shield is rotated forward on the spindle stem until~ the shield clears the kingpin bosses. Then four 3/8-inch holes are drilled in the spindle, corresponding to the position of the holes in the shield. The two holes closest to the bosses are tapped to take 7/18-inch bolts while the other two take 3/8-inch nuts and bolts. Tap them all if you prefer.

In adapting the Ford spindle to the Buick drum, use the stock Ford drums. The inner and outer bearing race portions of the hub are cut off at the seat. The hub portions are then machined to an outside diameter as that of the inside diameter of the Buick hub. Press the machined portions into the Buick drum hubs after the Buick races have been removed. Use about a .001 press fit. In this manner you can use stock early Ford bearings and grease seals.

The only current kit shoe brake conversion to '37-'48 Ford spindle is offered by Vic Hubbard Speed & Marine, 21040 Meekland Ave., Hayward, California. The kit allows use of '55-64 Chevy brakes, drums, backing plates and wheels. The steering arm is not included. No arm is needed on '28-'34 Ford spindles. A special steering arm is needed when using with '35-'48 Ford, available at extra cost. We don't know how this conversion is made but you can write Hubbard for details and price. They also have a line of disc brake setups so ask for a catalog.

Another swap around a long time that has recently really caught on is the early GM spindle and brake unit changeover. Use the 1941-'55 Pontiac; 1937-56 Olds; 1949-54 Chevy; or 1953-62 Corvette.

There are two ways of installing the GM spindle on an early Ford beam axle. The first is to ream the Ford axle kingpin holes to .859-inch inside diameter, so the GM kingpin can be used. This is beat done with an expansion reamer but it takes a while. When you do the job, have the new kingpin to measure with your one inch micrometer. After you have taken a mic reading, start reaming. After each ream use a telescoping gauge (snap gauge) to find the inside diameter. Then take a mic reading. Take about a quarter to a half turn on the expansion reamer nut each time, depending on reamer used. Most important is not to overload the blades or they will possibly brake or chatter. You will notice that if you turn the nut equally each time the reamer will remove the same amount within about .001-inch. In this way you can calculate what you will take off by how much you turn the nut on the reamer. This is important when you get down to the last few thousandths. When you do start making the finish passes, go about .001-inch each time and test the kingpin for fit. When the kingpin fits the bore with a hand press fit or when you can tap it through with a hammer, you're home safe.

The other choice is to make or have made a set of bushings for the GM spindle to fit early Ford kingpins. Use a quality bearing bronze for the bushing. Machine the bushing by first chucking up a 1-1/8-inch diameter bar of bronze bushing stock in a three-jaw lathe chuck with about 1-1/2 inches protruding past the jaws. Our spindle measured 1.055 inches inside diameter for the bushing but measure your own. Add about 1/2-thousandth (.0005) to the outside diameter for a press fit. Turn the bar to your diameter the length of your spindle boss height. Next, center drill, and drill to 51/64-inch a little longer than the bushing length. Cut off with a lathe parting tool to length. Measure the spindle boss for the grease fitting hole height, center punch, and drill a 1/4-inch hole in the bushing. Press bushing in spindle boss with the grease hole aligning with the boss grease fitting. Now ream the bushings to an .812-inch inside diameter with either an expansion reamer or Ford kingpin reamer.

The kingpin bosses are all the same height on '28-48 Ford axles, 2-3/8 inches. Some GM spindles, such as some of the Olds, have enough space between the kingpin bosses to place the 1/2-ineb tall stock Ford or GM spindle bearing. Some of the spindles, like the '49-54 Chevy spindle, do not have the room so a special bearing must be made. Use roller assembly NTA 1423 and two races. This bearing has a total height of .327-inch. A chromed axle could possibly have enough chrome on the kingpin bosses that you might have to shave, say maybe .010 off the boss bottom to get the bearing to fit. Some Chevy spindles have a little more room than others and the bearing will just slip in. Some axles have to be machined regardless, because the boss bearing surface has been chewed. The thrust bearing is of such close tolerance that an uneven race surface will keep the bearing from working. The race will settle to the shape of the metal supporting it. The best way to get an even surface is to mill.

The easiest way to set up to mill is to use a vertical end mill. First set the spindle head on its 00 marks in a vertical position. Next, place a drill chuck in the spindle with a dial indicator in the chuck. Securing the axle~ to the table can be done in different ways. One is to use an angle vise placed at either end of the table with the jaws parallel to the length of the table. Turn the axle upside down and place a new kingpin about one inch into the boss. Set the axle end in the vise with the other end hanging over the opposite table end. If you have a chrome axle, use copper sheet on the vise jaws. Use a bubble level on the front and side of the kingpin to find the vertical position. Then pull the vise snug, but not tight.

Position the dial indicator in such a way that you are able to move the axle up and down so that the indicator runs the full length of the kingpin. If the kingpin is straight up and down there will be no measurable difference. If you set the dial indicator on 0~ at the top of the kingpin side and move it down with a plus or minus reading at the bottom, the kingpin is not straight up and down. By using a wedge of sorts or a machinist jack under the opposite axle end, the left-right adjustment can be made by moving the axle up and down. The fore and aft adjustment can be made by moving the vise on its axis. Because the vise moves in one direction from 00 to 450, you might have to turn your vise around so the adjustment is in the opposite direction if the pin cannot be aligned in the first direction. Once you reach the 0 at the top to 0 at the bottom on both sides of the pin, remove the drill chuck and install an end mill or flycutter.

If you don't want to mill your axle (and try your luck), a smaller thrust bearing is available. It is roller assembly NTA 1423, the same as the last bearing with 1/8-inch rollers, but with a static capacity of 5980 lbs., and basic dynamic capacity of 2500 lbs. Use TRC 1423 races which are .095-inch thickness, .029-inch less than TRD 1423. If the axle bearing surface is rough, and some are, you're pushing your luck without milling.

The grease retainer can be machined several ways. Any grade aluminum or mild steel will work. If you have a 1-5/8~inch bar, chuck it up in a three-jaw lathe chuck with about 1-1/2 inches protruding from the jaws. Face the end and center drill. Drill about 3/4-inch deep with any drill between 3/4 to 1-3/8-inch. Finish the inside diameter with a tool bit or boring bar. Next, cut the race recess, measuring depth of cut by micrometer collar on cross slide, inside micrometer, telescoping gauge and a one to two-inch micrometer, or vernier calipers. Verniers will also measure the length of the cut easily, as will a one-inch depth micrometer. When the inside has been machined, 180 or 220 emery cloth the recess for any burns and radius the inside edge. lf you started with a larger bar, turn to diameter before cutting to length with a lathe parting tool.

If you have some 5/16-inch aluminum scrap about the diameter of the retainer, you can quick-n-dirty machine it out in no time. Find approximate center using dividers and centerpunch. Using the dividers, scribe the outside and inside diameter lines. Hacksaw or bandsaw off, close to the outside diameter, any large protrusions. It just takes longer to machine if you don't. Place a 3/4 or one inch parallel in a machinist vise with the plate on top. Secure the scrap and center drill after sliding the parallel out. Drill a 1/2 or 3/4-inch hole to match whatever size nut and bolt you have that is about three inches long. Really cinch the nut down on the scrap so it won't spin on the bolt. Slip the bolt in a three-jaw chuck until the nut touches the jaws. Tighten the jaws so they hol~1 the bolt, but don't screw the threads up too bad. Ya gotta use that low-budget mandrel one more time, not counting getting the nut off after the first time. Take light passes to keep from spinning the bolt in the chuck. When you reach the diameter by eyeballing the scribe or using a mic' or vernier, disassemble your nifty mandrel. Place the retainer in the chuck again and eyeball for runout as the chuck spins. If it is in the jaws crooked you can see it wobble back and forth as you stand at the lathe in normal position. Don't worry about the hole not being true to the center because it bobs up and down when you look at it from the end of the lathe. Just get the retainer face true in the direction the chuck spins by eyeballing. A tool bit works a little better than drilling the hole and using a boring bar because of the lesser pressure against the retainer, As the hole gets bigger, the sides get thinner, and the retainer starts to collapse under jaw pressure. When you reach inside diameter, then cut the recess as in the first method.

Now press your retainer on a race. The outside diameter of the race is sheared, which means that it is not exactly round; that there are numerous low spots. If the race is loose in the press fit, remove race and peen edge of tight side to make the inside diameter even smaller. Place the race through loose side and carefully seat race with a brass drift punch and hammer. Place the unit on a flat piece of metal like an anvil or vise column to do this. With the bearing and the other race installed, the loose race should rotate freely. Install on axle with pressed race at the top. It takes about 20 minutes to do this whole thing with no coffee break or messin' around.

When it comes to kingpins, the GM pins will bolt right in after you have carefully ground a new notch. Assemble the spindle to the axle and set the kingpin in until it is equal distance from the end, on each end. Mark center of axle hole on kingpin with any method of your choice and remove. Grind a small notch and replace to check for notch height and kingpin bolt fit. If you're too far up or down from the center, grind on the short side to center the notch and recheck. Try to grind a notch similar to the Ford bolt shape. When the kingpin bolt can be seated snug with a hammer, with the head still out one end and enough threads out the other for a lock washer and nut, you're home safe.

With early Ford kingpins you use the '37-41 pin which is 5-1/2 inches long. Remove the top retainer so the pin will fit under the GM grease retainers. You will possibly have to grind a new notch, check to be sure. On GM spindles that use the 5-1/4 inches kingpin length use the '37-41 Ford kingpin and measure the axle/spindle combo to see which end to grind off, or both, to retain the stock notch. Use an abrasive cut-off saw or grinder.

You will have to fabricate a steering arm if one did not come with your spindles. You may have to shorten your tie rod. This depends on what axle you use. A dropped axle will have the kingpin bosses closer together than stock, but the stock axles also vary in total length, plus spring perch hole distances vary. Put your front end together and try your tie rod, it might fit as is.

In order for the Ford tie rod ends to fit the GM steering arms, the tapered tie rod holes must be enlarged. Both the GM and Ford tie rods have the same taper angle and use the same taper reamer. It is possible to ream the GM steering hole from either side so the Ford tie rod could be placed on the top or bottom for radius rod clearance. A tie rod could also be made from 13/16-inch outside diameter .190-inch wall thickness seamless tubing. All you will need to do is tap the inside diameter with a 1/2 x 20 tap. If you have a right and left hand tap, you will be able to make a tie rod that you can adjust like the Ford. If you use a right hand tap on each end, one end will have to be removed from the steering arm to adjust toe-in.

You will also have to change the axle camber. Our reference shows 90 kingpin inclination on '28-'34 Ford axles and 80 on '35-48. 1949-59 Chevy is 40, '37-'48 Olds is 4~5/60 and '49-52 is 50, That is a sampling of only a few of the differences. All it really shows is that you have to bend the axle.

One way to figure how much to bend your axle comes from Ace Brake & Wheel Service, 1415 25th Street, Bakersfield, California 93301, Owner Fred Ousley, suggested a method to save the owner a small fortune in shop labor, if he could find a shop willing to do it. He said that to bend the axle a half to a full degree was relatively easy. The trouble comes when bending a substantial amount; the kingpin caster will wander, you sort of chase your alignment all over the axle because of the extreme pressures needed to bend it while in the car.

His method is to place the axle in a vise with copper jaw covers, preferably a large vise, lay a straightedge horizontally from the inner kingpin hole edge on one side to the opposite kingpin hole edge. Level the axle with a bubble level. Next, assemble the GM spindles on the axle and place a level on any machined surface that is true to the brake drum axle center. This could be the machined surface for the backing plate or the bearing locating surface on the spindle end, The spindle will visibly point upward but you will need the level for measuring how much to bend the axle until the bubble hits level,

If you are lucky enough to have or find a dropped axle that is really sway-backed, no problem bending it. Place the axle in a hydraulic press, belly up, and place wood blocks wherever the axle touches the press. We used a 250-ton press that wouldn't take no for an' answer, but a smaller press could easily work. Press equally along the axle between the spring perches to straighten out the axle. At the same time the kingpin angles are lessening due to the axle bending. It's trial and error any way you bend it, so level the axle, replace the spindles, then check with your level after each time you bend.

Once you have leveled the axle, then you are ready to twist it so the hole centers on the same plane. Four steel rods, about a foot and a half long, are pressed into both the kingpin and spring perch holes, Looking at the axle from the end shows any twist in the axle. If you are going to run parallel wishbones, don't worry about the twist of the spring perch holes. If you are going to run a stock type or split stock type wishbone the spring perch holes must be parallel. If not, the stock wishbone will not fit without forcing and will misalign the kingpin holes. The split type will bolt on with no problem except when the wishbone ends are bolted to the chassis at equal points in height, they will twist the axle.

We left the axle in the vise and used a 24-inch adjustable end wrench over the spring perch boss to twist the axle. It bends easy, so be careful. If the perch holes are parallel but the king-pins are not, secure the axle at the perch bosses and grip the kingpin boss with the wrench and bend in the right direction. Eyeball with rods in place, or just use a level on the kingpins when using a parallel wishbone setup where the perch hole misalignment is not important.

With the new axle installed, alignment is the standard procedure most competent front end shops can do with no problems, little time, and little money.

Ken Mitchell, the front end alignment man at Haberfelde Ford in Bakersfield, gave me more information on beam axles. Ford beam axles are made of Canadian steel and are tempered. It is the temper that gives the axle the life to hold alignment. When the axle ends are heated too much it draws the life out of the steel and it becomes a dead axle. A live axle, when being bent, will be moved 2~ to 30 past the desired angle because of spring-back. A dead axle is easy to bend and will bend right to shape, no springback. As easily as it bends to shape, the car weight and road bumps will bend it back out of shape, pronto. Ken recommends bending any beam axle out of the car if it needs more than a half degree camber change. He uses right and left hand benders called 'crows feet," These should be used when changing camber on a dropped axle when only the area between the spring perch boss and kingpin boss is being bent. You can preheat the axle end to about 3000 F., but not enough to make the metal change color. When the axle changes color, it loses its temper, and becomes soft. If you have a dead axle it can be retempered by a professional heat treating shop,

 

Middle '60s Falcon spindles can be adapted to Ford axles, but the area between the spindle ball joint bosses where the axle end would go is way too large. A section is cut out of the longest part of the yoke and the ball joint boss is lowered to the top of the axle boss and the yoke welded back together. Don't forget your spindle bearing when you clamp the yokes on the axle boss before welding. Align the two ball joint holes, weld the yoke, then drill the joint holes 5/8-inch diameter. The kingpin axle boss hole will be slightly smaller and pre-war Chrysler Corporation (Dodge or Plymouth) kingpin bushings are used. A set screw in the axle boss will locate the kingpin. There are many easier and better conversions than this, so don't do it; your life is riding on a weld.

A better spindle swap to the '28-48 front axle is the Econoline spindle. Our records show the '60-63 spindle will definitely work and we assume the '64-68 Econoline spindle will also work. There is a fair amount of machine work in this conversion. The Econoline kingpin is 1/16-inch smaller in diameter than the early Ford pin. An axle boss bushing must be made to make up the difference.

Make the bushing from 4130 or stainless steel. These can be machined from either tubing or a solid bar. Because of the extreme thinness, this bushing can collapse under the holding of the work or when installing the sleeve in the axle boss. To machine it out of a solid bar, start with a piece long enough to be able to turn a length 2-1/4-inch long with a diameter at least .825-inch. If your bar is out of round as the chuck turns, the extra diameter will allow you to clean the diameter to .813-inch. File a notch in the center of the bushing length 3/16-inch deep, 1/2-inch wide, and 11/16-inch long. Center-drill and drill with a 23/32-inch bit a little longer than the bushing length. Measure the Econoline kingpin with your mic' and use a small boring bar to reach the inside diameter, giving yourself about a .0005-inch (1 /2-thousandth) press fit. After reaching the right inside diameter reading with a telescoping gauge (snap gauge) and outside micrometer, cut the bushing off at 2-1/4 inches from the end with a hacksaw. You are taking a chance by cutting it off with a lathe tool or an abrasive cut-off saw because of how thin the bushing is (about .031-inch). Use a 32-tooth hacksaw and carefully cut the bushing off as the chuck rotates at about 100 rpm. You can also cut a shallow groove first, shut the machine off, then saw it off, following the groove.

We suggest the tubing route using 7/8 outside diameter, 3/4 inside diameter or smaller. Use the same procedure as the barstock except you won't need to centerdrill.

The way we would do it is to first mic' the kingpin boss. If it is wallowed out a little use an expansion reamer, as outlined in the '49-54 Chevy shoe brake conversion in this story, and ream until the hole is round, We would then mic' the new hole and add .001-inch to the bushing diameter. We would use 4130 tubing with about a 5/8 or 11/16-inch inside diameter, 7/8-inch outside diameter, turned to the correct reading with a press fit for the axle bore. Use a lathe parting tool or abrasive cut-off saw and cut to length. Press the bushing in and use expansion reamer to ream for fit.

The axle boss opening in the spindle with the bearing in place is 2.270 inches, 1/8-inch too small for the 2-3/8-inch axle. Remove about 1/16-inch off of both the top and bottom of the kingpin boss. A 1-1/2-inch counterbore with a 13/16-inch pilot can be used in a drillpress. Set the press at its slowest speed and place a 4 x 4 x 6-inch block on the table. Mic' the boss height before cutting. Place the axle boss on the block and grease the kingpin bore so the pilot won't gall. Make progressive cuts until you have taken almost 1/18-inch off the top and bottom with a total height of 2.270-inch. Measure this with either a 2-3-inch micrometer or vernier calipers, and if it is more than 2.270-inch, cut again until it is the right height. You can also use the milling procedure as outlined in the '49-54 Chevy shoe brake conversion in this story. The counterbore will work well because uneven surfaces do not affect the stock bearing as easily as a Torington bearing.

Taking 1/16-inch off of each side keeps the kingpin locking bolt slot in the center, but a new notch must be ground. Grind the notch 1/32-inch deep, 3/16-inch wide, and 3/8-inch long between 90 to 180 degrees from the original slot. Use the early Ford locking bolt and acorn nut.

We have no reference to an adaptation such as the next one but it would be a clean way to go. Instead of making a bushing for the axle, ream the spindle bosses for early Ford bushings. Press fit the bushings and trim the ends, if necessary, when the bushing grease hole aligns with the grease fitting of the spindle. Measure the total Econoline spindle boss height and select the Ford pin that will fit, possibly you might have to grind to shorten the '42-'48 Ford pins if they are too long. Use the early Ford bearing and cut the axle boss height to match.

Our records show that the Econoline kingpin inclination is 7-1/2, which is just enough to make it easier to bend the axle out of the car. Axle bending is covered in the early GM spindle-to-early Ford axle conversion in this story.

The Econoline spindles have a stop device on top of each tie rod boss that might be saved, but they can be cut off and ground or filed smooth. The left spindle (driver's side) has an integral, curved steering arm that can be used with a hot rod type drag link. If the steering arm length from the center of the kingpin to the drag link pivot on the end of the arm is too long, it can be cut-off and dressed, with the addition of a custom steering arm. Too long a steering arm means that the wheels will not turn fully in either direction beforethe steering box locks. A custom steering arm the correct length or a longer pitman arm is the answer. Also, the early Ford tie rod will fit the Econoline spindle.

Disc brakes have been around a long time, the first registered in 1902. Since then many designs have been introduced, tested, and shelved. One of these was developed by Joe Milan at a cost of $250,000. The Kinmount Manufacturing Company took a license from Milan to manufacture them during and after WWII. They were called the Kinmount Safe Stop D/sc Brake.

Because most cars in competition in the late '40s and early '50s had early Ford running gear, - Kinmount brakes were demonstrated on early Ford cars. These brakes are a bolt-on item to early Ford. They could stop better than any brake Ford had produced. They were disc brakes but had a floating disc inside a closed housing. It worked on the principle of an engine clutch unit.

Picture in your mind coasting down a bill with the engine dead because you have seized a piston and you are in 3rd with the clutch in. The flywheel is very stationary and so is the pressure plate, but the disc is spinning freely. Slowly let the clutch out and you eventually come to a stop. Let it out quick and you'll eat a steering wheel. Let's call the flywheel a backing plate with the axle running through the middle. There is a disc against the backing plate but it has splines on the outside diameter that interlock with the wheel drum. Next we have a pressure plate anchored to the backing plate. The backing plate does not move so the pressure plate does not move either. The disc is free and moving because it is interlocked with the drum like the disc is interlocked on the tranny mainshaft and moving while in gear. When the clutch is applied on each they both come to a stop.

Probably the most notable thing about the Kinmount was also the biggest drawback. Because of the high degree of pressure that could be applied in the brake, a high degree of adjustment had to be maintained. They had a habit of erratic braking. The slightest misadjustment meant one wheel locking or switching lanes when you hit the brakes. To keep these brakes in tune and drive your car 1000 miles a month was like having two wives, they both needed equal attention and could fly off the handle unexpectedly.

So you're the proud owner of a set of Kinmounts you got at the swap meet for 200 bucks. Let's hope you have two left (front and rear) and two right. They are marked on the casting to designate which is which. The rear brakes have the emergency cable hole in the backing plates. The wheel drums are aluminum, so look for cracks to repair.

To put these on your first love, start with a brakeless spindle. Because the backing plate is thicker than stock, install it with longer grade 8 bolts or socket head capscrews and lock washers or locknuts. Be sure to install stock Ford grease shield. The disc is next, followed by the pressure plate, which is aligned and held in by spring straps on the backing plate. Mesh splines of the drum edge to the splines of the disc and cinch the drum down like it was early Ford (because the hub is early Ford). Check to be sure the drum vents face forward on all the wheels.

The easiest part of all is the most critical; adjusting the brakes. Two adjusting nuts vary the distance between the pressure plate and backing plate. If they are not basically equal in adjustment all the way around, they will brake most unevenly. Have fun.

The most popular and successful disc brake design has been the spot" disc brake pioneered by WWII airplanes. American cars didn't get widespread use of the spot disc until 1965. Prior to '65 most of the disc brake kits for competition cars or hot rods were expensive and few were manufactured. Some ingenious rodders built their own conversions while others had one-shot special order brakes built by professionals. If you spot an unusual disc brake set-up for early Ford at a swap meet and the sellers don't know who made it, chances are they really don't. Some kits were made up from several different manufacturers' parts. One of the more popular was the Bell Auto-Airheart disc kit.

The Bell Auto-Airheart disc brake kit is composed of the Airheart alloy single or dual spot caliper and appropriate disc. There were different size discs that could be adapted to most American car hubs. The cars used on the street usually had the Meehanite iron disc and alloy hubs were available for competition. The kit also came with a caliper bracket to mount it to the axle, and necessary bolts for a complete set-up.

Bell engineered the early Ford adapter kit around '42-'48 front hubs. These hubs are slightly shorter between the bearings and have a flat surface on the inside of the brake drum. With these hubs, assembly is just a matter of removing the stock lug bolts and installing the iron disc.

To remove the lugs, first press the hub out of the drum. When the lugs were pressed in at the factory, a small ridge was left at the base of the stud thread to help hold. Cut this ridge away, if possible, before pressing out the bolts. Be double sure that when you press the studs out, you have super close support around the stud head under the hub. Don't beat them out with a hammer, you could bend or fracture the hub easily. After special lug studs are screwed into the disc, the hub is pressed onto the serrated stud shoulders. Face of hub and disc must be absolutely parallel.

Pre '41 hubs must be machined because of either a slightly angled rear flange surface or small ridges running from the hub diameter outward to each lug hole. The lathe setup is done with a four-jaw chuck. Chuck up the hub by the small bearing end. Place a dial indicator on the outer edge of the flange to find 0 runout by rotating the chuck then adjusting the chuck jaws till the hub is centered. Next, place the indicator so it reads the hub surface that faces the drum. Rotate the chuck to find and eliminate flange face runout. Tapping with a hammer at the low spot on the inside part of the hub where the indicator designates will correct runout. Tap ever so softly if you leave the dial indicator in place. Once again, check runout of the flange diameter. It is quite possible that the circumference is not true, so as long as the indicator needle wavers plus and minus over 0 in one hub revolution, you're about center. Readings can also be taken from the large con race locater surface. DO NOT get discouraged if dial indicating seems impossible, it's just very difficult to master. DO NOT eyeball engineer it either, it won't work. If you have a ball bearing dead center large enough to support the small bearing end of the hub, turn the hub between centers. This procedure is found in the Herbert & Meek 'Vetteto-'49-'54 Chevy spindle conversion in this story.

When the hub is centered, the angled flange area must be cut perfectly flat. If you are not sure about how secure your hub is in the chuck, take light passes about .015 or .020-inch deep each until flat. If the hub is not in tight and the cut is too deep, the pressure of the tool bit hammering against the ridges will dislodge the hub.

The discs have a locating hole 4-1/2 inches in diameter so machine the hub flange a bit smaller to clear the disc hole. In addition to making this area flat so that the disc can bolt up flush, the machining is necessary for proper caliper/disc clearance. Because the disc is rotating within the two caliper lips, the smallest deviation will cause interference. About 1/8-inch must be machined from the early Ford hub flange back to get proper caliper/ disc relationship.

To install the kit, first bolt on the caliper bracket in the backing plate position, using stock backing plate bolts. The hub is then installed, after the disc has been bolted on, with all bearings, and snugged up with the spindle nut. The caliper only fits one way on the bracket and then check for clearance. There should be about .062-inch between the caliper and disc on each side. By eyeballing, the line where the caliper breaks apart for servicing should be right in the middle of the disc edge.

The caliper should never be spaced by using shims between the caliper body and the bracket. The maximum strength was engineered to be when the caliper and bracket are bolted directly together.

Obtaining the correct clearance for the disc can be done by cutting the hub flange again where the disc rests (oh boy), or by making a small inner spindle bearing spacer. Either way, the disc will be moved toward the outside, which is generally the way it will need to go. A very slight amount of clearancing toward the inside can be done by machining the entire face of the bracket. This can be done by dial indicating the face in a three-jaw lathe chuck, or milling. We recommend surface grinding, which is the quickest and most accurate method. Only a few thousandths may be removed, though, otherwise strength is completely lost.

With everything in place, there should be approximately .095-inch clearance between the disc and the caliper bracket, and the disc should run perfectly true. If not, get it that way because your life depends on it.

 

On the early Ford rear end, the problem takes on a new dimension. Some trial and error fitting is required. The brackets - will interchange from front to back because of the same backing plate bolt pattern, Distance from the bracket to drum centerline is also nearly identical, making the disc/caliper installation relatively simple,

The rear drums are disassembled just the same as the front drum. 1947-48 drums are completely flat across the brake side, but earlier drums have triangular recesses between each of the stud holes. There is no machine work needed on the rear hubs to accept the disc brakes. Machine work may be required to get proper disc/caliper clearances.

Because of the early Ford tapered axle end, the disc can be too far or too close to the mounting bracket. If the disc is too close it can be spaced outward by using cone shaped axle shims available through most antique car parts suppliers. If you feel energetic, make your own shims from sheet steel in varying thickness. The thicker the shim, the further the disc is moved away from the bracket, When using these shims the axle nut must be pulled down TIGHT. If not, the slightest movement will chew a shim to shreads which precludes snapping an axle key. Shim or no shim, if the axle nut is not tight enough, you could snap an axle shaft right behind the drum hub when you nail it to the floor.

If the disc is too far away, best correction is to use spacers between the caliper bracket and axle housing. It is quite unlikely the two axle ends will require the identical spacing adjustment. Use the same .095-inch bracket-to-disc clearance on the brakes and the caliper line should split the edge of the disc. In case the calipers touch specialty wheels, some clearance can be realized by sawing off the outside piston caliper shafts at the snap ring groove. A little metal can be removed from the calipers, but only a little,

The Bell Auto-Airheart kit will fit all '42-48 Fords and will fit '28-'37 with some minor modifications. The '28-34 backing plate bolt pattern is just slightly different, which can be taken care of with a rattail file on the caliper bracket, and hub spacing must be modified by use of spacers on the spindle. The calipers are also designed to take the standard Ford 3/4-inch hose.

Bell lists only brake rebuilding kits in their catalog, and these are for Hurst/Airheart units. A letter to Bell should answer any question we didn't in case you have one about this kit.

A conversion similar to the Bell Auto that is being done today is with 1965-67 Mustang discs (because they are not the floating type). Bell used a '42-'48 front drum because of the shorter bearing distance but in our research we found the '35-48 drums have the same bearing distance. Disassemble, remove studs, and chuck up in the same manner as outlined in the previous Bell Auto-Airheart method.

Measure the inside diameter of the rotor locating hole and machine the hub flange to that diameter with a locating shoulder height of about .125-inch. This machine set-up is outlined in the Herbert & Meek 'Vette-disc-to'49-'54 Chevy spindle conversion in this story.

When you place the hub into the rotor it will be quite obvious that the hub flange is much larger than the rotor hub. This can be machined down to the diameter of the rotor hub but do it before you remove the hub from the lathe.

The early Ford 5-1/2-inch lug pattern is too wide for the smaller Mustang rotor, so the easiest thing to do is to use the original Mustang pattern. Place the early Ford hub, outer bearing down, on parallels in either a vertical end mill or a drill press so the drill does not hit the table. Set rotor on hub and locate shoulders. Use a 1/2-inch bit and drill through the Mustang lug hole into the early Ford hub, Drill one hole, disassemble rotor from hub, chamfer burrs from hole edges with a hand chamfer tool or a larger drill bit than the 1/2-inch. Place rotor back on hub, and using a 1/2-inch bolt and nut, bolt tightly together and drill the other four lug holes. Split the unit and deburr the drilled hole edges.

Make caliper brackets from 5/16-inch hot rolled steel plate. The bracket dimensions that fit the early Ford spindle are the same as those on the Volvo adapter. You will have to measure how high to mount the caliper on the bracket but mount the caliper horizontally on top. To lay out the plate for machining use the procedure for the Jag wheel lug adapter in this story, and that is to make the measurements from one centerpunch. Machine the bracket, also using the Jag procedure for lathe set-up and drilling. After the plate is machined and the edges deburred, surface grind or Blanchard grind for trueness.

Two small spacers are needed to space the caliper away from the bracket. If the rotor is off to the outside make the spacers longer to reach the rotor. For openers, make the spacer outside diameter about that of the caliper surface around the bolt area. Make the inside diameter that of the attaching bolt size. If you are lucky and have some thick wall tubing that matches the description, cut off four pieces of equal length that are long enough to keep the caliper off the bracket. Cut them in an abrasive cutoff saw, or by a parting tool in a lathe.

If you don't have the tubing, use a solid bar of the right diameter. If you have a bar that is larger in diameter, machine to size first, then center-drill and drill with the bit that matches the bolt size. If you use a lathe parting tool for cut-off, chuck up as close to the jaws as you can. Deburr outer edges with a file or belt sander and the inner holes with a rattail.

Use '37-48 Ford spindles with no machine work and stock bearings. Assemble unit with sockethead (Allen) cap screws which are grade 8, or grade 8 bolts which have six lines radiating from the center on the head. If the rotor is off, it can be adjusted in either direction by the caliper spacers, or by putting a spacer between the hub and rotor which moves the rotor toward the caliper only. One other possibility is to use a thicker plate for the bracket and not make the caliper spacers longer, if there is enough room. The idea is to keep all the parts as short as possible to reduce pressure due to leverage during braking.

The easy way out of it is to get a conversion kit from Contemporary Chassis. It will have all that is necessary to do this job.

Another Mustang disc conversion is one that we lack full information on how to make. This conversion uses '68 and later Mustang discs which have full floating calipers. This involves, among other things, a bunch of spindle bolt figuring and machining, Believe me, it can be done because somebody down at Challenger figured it out. They have an adapter kit that consists of two machined and sleeved spindles, two caliper brackets, inner and outer bearings and oil seals, retainer nuts and special bolts and spacers. With this kit, Mustang discs are a bolt on. Write Challenger about this and other disc kits.

There is a third way to put Mustang discs on an early Ford spindle, Not only do we not recommend this to the brake swapper, but we wouldn't touch it with a ten-foot pushrod. This swap is based on a spindle bolt swap. It is a matter of machining an early Ford spindle bolt off and welding on the Mustang bolt and flange. The rest is a stock bolt on, But let's get back to the spindle. Your life rides on a weld. If welds were 100% effective, nobody would require magnaflux certificates for safety. Don't get me wrong, you can normalize the weld but welds can crack. If I were to run a set of welded spindles I would have them magnafluxed at least once a year. You be the judge.

Hamilton Automotive Industries has conversion kits for both the floating and nonfloating Mustang/Cougar disc brakes. The only difference between the '65-67 Mustang and the '68 Cougar is the caliper mounting, so the early Ford spindle is machined the same for each rotor. Because the bearing centers are closer together in the Mustang disc than the early Ford drum, the spindle must be shortened. First the washer tang slot is extended on a vertical or horizontal endmill. Curt Hamilton feels the lathe set-up is a trade secret but the spindle bolt is turned in a lathe. The large bearing end of the bolt is turned down .030-inch to accept a Timkin LM 67043 cone and it fits in the stock Mustang cup. A grease seal spacer is used on the big bearing end so that the stock Mustang seal can be retained. The small bearing locating diameter is extended toward the inner bearing. Extend the threads by lathe and drill a new 1/8-inch cotter key hole the distance of the difference between the early Ford and Mustang bearing centers, cut off the excess threaded bolt with a lathe parting tool.

Both kits are available with or without rotors and calipers, and all the necessary fasteners and brackets. You can send in your own spindles for machine work, or there is a spindle exchange program, or you can buy them outright in the kit. He also offers the rod type steering arm at extra cost.

1960-68 Econoline spindles that have been adapted to '28-48 Ford axles (as outlined in the Econoline drum brake and spindle changeover in this story), can be adapted to disc brakes. Use '65-'67 Mustang/Fairlane discs and calipers. All that is needed for this conversion is a bearing spaces to space the bearings to fit the Econoline measurement. Remove the outer race and measure the diameter. Also measure the spindle bolt bearing small end. The spacer is made from steel 1/4-inch thick, the diameter about .005 less than the race diameter and the inside diameter about .015 larger than the spindle bolt. Two machine set ups for the spacer are outlined in the Chevy spindle/drum brake conversion in this story. Place spacer in hub and press race over it, bolt the rest together. An adapter kit is available from Contemporary Chassis Design as are other changeovers, write for information.

Volvo discs for '40-48 spindles are another sanitary way to go. In order to find out more about this brake I contacted a roundie-rounder racer in mini-stocks that ran Volvos. Milton Webster of Oildale, California said that according to his manual, which only went through '70, the 122S rotor was nine inches tall and was available from '59-66. But the P1800 sports car and P1800 station wagon from '62-70 also had the same brakes. He said that the Volvo lug patterns were of the Ford-Plymouth type and not to use Plymouth rims because the lug bolt seats were substantially larger than the Volvo lug nut and the nuts would suck through the rim easier on a hard turn, He went on to say that some Ford station wagon rims wouldn't fit over the rotor hub and that he had to grind a bunch out of the center hole for fit.

To follow up on these tips I went to Haberfelde Ford in Bakersfield, and talked to the assistant manager, Gage Burr. He said that the '65-71 Ford station wagon rim had a 2-7/16 inside diameter machined locating shoulder, much smaller than the other Ford rims, to fit on the machined axle end. The 15-inch, extra wide rim was dropped in '72 and the large hole center is now being used on all Fords. There are three manufacturers of rims, which means some rims are riveted and some are spotwelded in the same model year. Don't use tubeless tires on riveted rims, they have a tendency to leak through the rivets. Fourteen-inch rims are passenger and 15-inch rims are truck.

The aforementioned Volvo model disc and caliper are needed for the conversion. The early Ford inner cone bearing can be used, but the outer cone bearing must be a Volvo part number CK-09074 or equivalent. Use the stock Ford spindle nut and washer.

A caliper bracket must be made of either 1/2-inch steel or T6 aluminum. The procedure for laying out the bracket is the same as the wheel lug plate for the Jag. The machining is also the same procedure. Refer to the Jag brake in this story.

The Volvo bearing centers are 1/2-inch narrower than the Ford. Make a 1/4-inch spacer the same inside diameter as the dirt seal and slide it on the spindle bolt before installing the hub. The spacer is made from a round bar of steel that is larger than the dirt seal diameter. Place the bar in a three-jaw chuck with about 1-1/2-inch protruding from the jaws. Face the end of the bar with a tool bit, then center drill. Drill bar with a 1-3/16-inch bit so the inside walls are over a 3/4-inch length. Next, take a three-corner file with the tip ground similar to a tool bit (or use a tool bit secure in a tool holder) and make a radius on the inside edge while the chuck is spinning to match the spindle bolt radius where it rests. Turn the bar to an outside diameter about .003 over the seal inside diameter to get a good seal. To keep the surfaces true, cut off the spacer with a parting tool while still in the lathe. Give the cut-off edge a little chamfer with a file or belt sander so it doesn't damage the dirt seal, and rattail file the inner edge.

Remember to use sockethead cap screws which are grade 8, or grade 8 hexhead capscrews (standard bolts with a six-sided head for a wrench). These are distinguished by six lines radiating from the center of the cap head. Use either lock nuts or lock washers. Also, 1970 Volvo brake hoses are quite long and will go directly from the caliper to the frame.

The rotor must be in the middle of the caliper and the adjustment is about the same as used on the Datsun rotor in this story.

Datsun disc brakes also take '37-'48 Ford spindles. They are used to adapt the hub, rotor and caliper off the front of a Datsun 1600 or 2000 roadster. These cars are no longer made so look for them in wrecking yards.

First chuck up the spindle bolt in three-jaw lathe chuck by the inner bearing area of the bolt. There is a slanted area between the backing plate locator and the spindle bolt. The locating shoulder is approximately 3.935 inches in diameter. Machine a new locating shoulder for the Datsun caliper bracket by machining a new diameter of 2.185-inch to a .156-inch depth at the new shoulder. Measure your bracket locating hole to be sure about diameter for spindle shoulder.

Place bracket over spindle bolt with the bracket recess facing the hub flange so the caliper would be in a vertical position. Cut and grind away all metal from the spindle flange that keeps the bracket from seating completely against the new spindle shoulder. Heliarc or wireweld the bracket to the spindle flange in at least five equally spaced places, give or take an inch.

Drive out the Datsun hub outer and inner races. Replace the outer with a Bower 05185 or equivalent, then place a Bower 05075 cone bearing into the hub followed by a stock Ford tanged washer. Add another spindle washer with the tang removed to keep the spindle nut from going too deep and running out of threads. There is also a spacer on the Datsun spindle bolt that must be expanded by heat, removed and replaced on the Ford spindle.

Replace the inner race in the hub with Bower 17244 or equivalent. Then a Bower 17119 cone bearing followed by a stock Datsun neoprene bearing seal to top off the hub. The rotor bolts to the spindle flange side of the hub with four bolts and the caliper bolts to the bracket with two bolts. Be sure the disc fits in the middle of the caliper. If not, add steel shims between the inner race and bolt spacer to move rotor out. Surface grind stock spacer or make a new spacer to move rotor in. The procedure to make a spacer is found in the Volvo-to-early-Ford conversion in this story.

Adapting E type Jag hubs to '39-'48 Ford spindles can be done in three ways. The first way is to sit down and figure it out yourself. You won't need to machine the Ford spindle. You will have to machine the inner bearing area of the hub a little larger in diameter to accept a Bower 15245 cup. Mic' the cup and machine for a .001-inch press fit. Chuck the hub up in a four-jaw as outlined in the Bell Auto-Airheart lathe set-up, except the face run out can be checked on either side of the rotor if left on the hub. Once the flange is indicated in, set-up a short (about three-inch long) boring bar to machine the inner bearing area. After pressing the cone in use a Bower 15118 cone and a 40185 seal.

A caliper-to-spindle bracket can be measured after the hub is bolted on the spindle. The bracket is about a half-inch thick and bolts to the axle side of the two front backing plate bolt holes. Use two 7/16 SAE sockethead cap screws to bolt the bracket. Insert the bolts through the bolt hole from the drum side of the spindle. Place washers over the bolts to space the bracket away from the uneven surface of the axle side of the spindle flange. The bracket is drilled and tapped for 7/16 SAE threads. Use either a self locking bolt, Loctite, or a jam nut on the threaded end with at least one full thread showing when nutted. When the caliper location is found on the bracket, drill the bracket and tap it to 7/16 SAE threads. Run the bolts through the two caliper holes into the bracket. Don't use jam nuts, not enough room between the bracket and rotor. Be sure the rotor runs true to the caliper pads and sits in the middle between the two. Remember, this is only a guideline and you may encounter problems we didn't see. If you are the machinist you think you are, you'll compensate.

If you're not a machinist, J & J Chassis offers a kit and a service to adapt the hubs. If you have machining and certified welding talents, they will sell you the kit pieces. Lastly, you can send in your '39-'48 Ford spindles, E type Jag hubs, rotors, and calipers and they will do the work for you.

If you don't want to run Jag wires, J & J also offers a conversion kit that you can buy as a kit or they can be put on when you send your brakes in for conversion. Then again you can make your own. It's relatively simple to figure but it must be accurate. All that is required is a lug plate that holds the wheel lugs and a spacer to keep it off the hub. Five socket head cap screws go from the inner side of the rotor through the spacer into the threaded holes that are staggered between the lugs in the lug plate. The reason for the spacer is to keep the lug heads off the hub so the spacer must be notched for the lug head diameter clearance. That is the principle.

To find the inside diameter of the lug adapter, first machine the hub to diameter, Set the hub up in a three-jaw chuck lathe. Use tailstock dead center to align end while securing jaws. After the jaws are really tight against the hub flange, with the knock-off threads facing out, machine the threads off. This can be done with a lathe parting tool or a lathe turning tool by progressively turning the diameter the length of the threads. Either way is your choice but machine the end of the hub off to the bottom of the threads.

Turn down the hub from outer bearing to the flange, the diameter of the hub near the flange, about 2.550 inches in diameter. Do not machine off any part of the radius at the hub/ flange intersect. Turn hub down no further than what it takes to just clean and true the hub area that locates the lug adapter. Also face the flange on the small bearing side to the radius at the hub/flange intersect. The hub can be turned .010-inch undersize from the small bearing end to a distance a little more than the thickness of the spacer and lug adapter from the flange face. This makes it a little easier to slip the adapter in place. You can also turn the hub between centers after the bearing bore has been enlarged. When turning between centers, all surfaces turned are true to the bearing axis and you are able to true all surfaces without turning the hub around to do the other side. Turning between centers set-up is covered in the Herbert & Meek 'Vette-disc-to'49-54 Chevy spindle.

The spacers are made of hot rolled steel that are the thickness of the lug shoulder length and the other spacer the height of the hub/flange radius. Be sure to centerpunch each piece in the middle for the layout center. It is best to cover the surface with blueing dye. Scribe a circle from the center-punch the diameter of the Jag rotor bolt pattern on both plates. On the lug plate scribe another circle the diameter of the wheel lug pattern of your choice. Centerpunch a point on the lug diameter and divide the circle into five equal segments with the dividers, Centerpunch the other four points on the lug diameter, Center-punch a point on the smaller diameter midway between two centerpunches on the large diameter so the holes will not overlap. Divide into five segments and centerpunch. Then take the dividers and scribe a circle around each centerpunch on the diameter of the spacer that leaves enough room for the wheel lug head to clear the spacer when they are assembled together. Scribe another radius from the diameter circle connecting the bolt radius to form a star shaped spacer.

Place each piece, one at a time, in an end mill or a drill press and secure the plates by clamping on the tables with 3/4 or one inch spacers underneath to keep from drilling the table. You can also use a machinist vise with spacers. First centerdrill all the punch marks on the lug adapter, then drill the very center hole with about a one inch bit. Drill the lug pattern holes to the size of the lug shoulder diameter, leaving a few thousandths for a press fit to hold the lugs. Drill the smaller diameter hole with a 25/64-inch drill and tap with 7/16-inch SAE tap. The best way to tap a straight thread is to place the tap in the drill chuck after you have just drilled the tap hole with a drill press. Apply light pressure with the tap in the hole and turn the chuck by hand, cutting threads about 3/8-inch deep. Loosen the tap from the chuck and finish the threads with a tap wrench. Center drill spacer holes, then drill the center one inch and the five diameter holes 7/16-inch.

Place the dead center in the tail-stock and slide the tailstock to the chuck, Whether your four-jaw chuck has reversible jaws or unboltable jaws, set them so you are able to grip the metal and rest the workpiece against the jaw while suspending the metal away from the chuck face. Slide the deadcenter into the one inch hole to center it. Ease the jaws down one at a time, little by little. Tap the work-piece with a brass hammer at the jaws to make sure it is seated against the jaws. Dial indicate the one inch hole to 0. This means the workpiece center and the lathe center are parallel.

Machine the inside diameter of the lug adapter with either a boring bar or a tool bit to a slip fit or .001 over the hub base diameter. Next chuck up the lug adapter in a three-jaw by the inner hole. Machine the lug adapter to diameter, leaving about 3/8 of an inch between the lug holes and the outside diameter.

The spacer can either be set-up in a lathe like the lug adapter and be machined to 3-9/16 inches inside diameter, or flamecut the hole. It is not that accurate of a hole. Flamecut the scribed outside shape, then file, grind or belt sand the edges smooth. Blanchard or surface grind the spacer and lug adapter for concentricity. Install the wheel lugs as outlined in the J & J Chassis 'Vette to '49-54 Chevy spindle in this story. Assemble the lug adapter over the spacer on the small bearing side of the flange. Use grade 8 bolts that almost reach the surface of the lug adapter. Use either Ny-lock bolts or Loctite to secure, and torque all bolts evenly.

Hamilton Automotive Industries makes a one piece adapter for five-lug rim to Jag hub. There is no difference between the J & J Chassis machine set-ups and machine operations and Hamilton's. Hamilton uses 3/4 thick, 1018 hot rolled steel plate for his one piece adapter. Lay out the two diameters the same as in the J & J five-lug to Jag hub adapter in the story. Instead of using the spacer plate to keep the lug heads off the hub, he counter bores the lug holes the diameter of the lug head the depth of the lug head. When the lugs are seated, they won't touch the hub and the adapters are installed like the J & J Chassis adapter. He has these available with different lug pattern diameters.

Contemporary Chassis Design has a super low priced, bolt-on Jag hub to early Ford spindle adapter kit. This kit contains new bearings to adapt the stock Jag hub to the stock Ford spindle and two caliper plates for Jag calipers. They also offer the service of adapting the Jag hubs to the five-lug rim pattern. Write Contemporary Chassis Design about this one, it's well worth it.

 

Larger, full fendered rods over 3000 pounds should consider vented disc rather than solid disc. Vented rotors provide about 25% increase in area for heat rejection by air flow as compared to a solid disc. Vented rotors also run cooler than solid disc and add to lining life.

Herbert and Meek did a disc conversion using vented GM rotors on '37-48 Ford spindles. This requires machining the early Ford hub to accept the GM rotor. This machine setup and rotor mounting is similar to the procedure found in the Bell Auto Airheart brake in this story. Sometimes a spacer/adapter is required for clearance between the Ford hub and rotor. There are no kits currently manufactured so you'll have to engineer your own brackets.

There are manufactured kits to adapt the Corvette disc to '49-54 Chevy spindles. Custom tube axles can be ordered from assorted manufacturers for the Chevy spindle. You can also adapt your own GM spindle as outlined in the GM shoe brake conversion in this story.

One of these conversions requires two '49-54 Chevy spindles with hubs, a pair of '66 or later Corvette disc brakes and calipers, brake hoses and fittings. S & J Chassis offers an adapter kit that consists of two caliper brackets and ten wheel lug bolts.

This is how it works. Drive or press the lug bolts out of the drum so you can get to the rivet heads and grind those off. Remove hub from drum and rivets from hub. The new lug bolts in the S & S Chassis kit have a serrated shoulder on them that lock in place when pressed in the hub. These lugs are available at any wheel and brake house but we don't know how long they are. The lug shoulder protrudes through the hub about the thickness of the rotor hub to locate the rotor. Use a 9/16-inch bit to drill the rotor lug holes to fit the new lug shoulders. It can be done using a hand drill but do yourself a favor, use a drill press.

A sure-fire way to get the studs in is done without a press. Acquire a hand full (8 or 10) of 9/16 or 5/8-inch flatwashers. Then place the lug in the hole and place the 30 wt. oiled washers over the threads. Leave enough to get a full set of threads in the nut. Grab your Mexican adjustable speed wrench and give 'er about four or five good turns. The oil keeps the washers from galling. Remove the nut and put some more washers on according to how far you went. Replace the nut and do it again. Keep stacking washers and turning the nut till the lug bottoms. Then give it about 40 ft. lbs. of torque to be sure. This procedure can be used on any lug bolt replacement and it works.

With the rotor/hub unit installed, a caliper bracket can be measured and made. Choosing a piece of hot rolled steel about 3/8-inch thick, use the upper and lower backing plate holes that face the front to anchor the bracket. The bracket bolts to the axle side. Set the caliper on the rotor to measure with. Be sure the caliper is high enough to clear the rotor as it turns, and making full lining contact on the disc. Drill your holes as you see fit. Cut the plate to make it look like a bracket but do it so it just clears the axle and the caliper. Don't clearance too far or you will loose your bracket strength.

The caliper must be spaced away from the bracket. Measure the distance between the caliper mounting surface and the bracket. Make the spacers as outlined in the pre-OS Mustang disc conversion on stock early Ford spindles in this story. When you buckle this operation together use grade 8 fasteners, whether socketheads (allen) or bolts with six lines radiating from the center on the head. If the caliper doesn't align dead-on with the rotor, back to the drawing board; it has to be right, If it fits but the caliper sets too far one way or the other, either make new longer spacers or trim the ones you have, depending on which way you need to go. The J & J Chassis bracket bolts on in less time than it takes to read this.

If your bracket works, cinch it down with lockwashers or self-locking nuts. Because this system was designed to be used with rear drum brakes, no pressure booster is required.

Herbert and Meek at one time offered adapter kits for '64 and later Corvette disc to '49-59 Chevy truck spindles and 'Vette disc to '49-54 Chevy passenger spindles. Due to minor engineering problems the home brake swappers didn't see or understand, difficulties arose. Herbert and Meek no longer supply these kits on the market but they are most definitely available for installation at their shop.

The '49-54 Chevy passenger spindle kit is very similar to the J & J Chassis kit. A phone call to Andy Herbert cleared the air on one of his older disc conversions. This conversion uses the rotor from the intermediate size GM car. It is smaller in both diameter and surface width than the 'Vette. The caliper used on the small rotor is a floating single piston type. Andy said the braking was about as good as the 'Vette but lining life was not as long. These floaters can be adapted, but not as easily as the four-piston 'Vette caliper which will work on the smaller disc. He recommends the 'Vette rotor because of the simple procedure of placing the hub inside the rotor. The smaller disc must have the hub placed outside on the rotor because it will not fit inside. Andy recommended trueing the hub-to-rotor surfaces on both the hub and rotor. He said the metal around the lug shoulders will raise a little sometimes I and the rotor will not fit flat on the hub and viceversa. This is one of the engineering problems brake swappers skipped over, which led to brake problems.

To true the hub flange use a three-jaw lathe. Chuck up a three-inch diameter bar with~ about 1-1/2-inch protruding from the jaws. Set the compound to 600. To be sure about which 600 you want, take the ball bearing dead center and set it parallel to the ways next to the compound. The nose angle of the dead center should be parallel to the compound side looking down from the top. If they are not parallel move the compound to the 3Q0 mark. Some lathe compounds are degreed with the 00 reference point being parallel to the ways (running lengthwise). Other lathes have the 00 point being perpendicular to the chuck turning center (running crosswise). Some lathes have both reference points on the compounds. These lathes will show a 300 at one reference mark and 60~ at the other reference mark which is 9Q0 around the compound base. If it seems confusing, just put the deadcenter up to the compound side and make sure the degree numbers 30 or 60. You are going to cut the three-inch roundstock to the same taper as the dead center, got it? After you have secured the compound base, the compound will move in toward the chuck from the left of the carriage.

If it doesn't move in that direction, move your compound degree. If it doesn't look right that way it is because you will run the spindle in reverse and cut the taper on the opposite side from you. Some lathes don't have a spindle reverse. It takes a little bit of rigging but you can get the taper cut on the side closest you, it's just a hard way to go.

Cut the taper with the compound, but only cut enough to give a true surface for the inner hub race to seat against. Now place the hub inner bearing on the new center and slide the tailstock ball bearing center into outer bearing race. Secure the tail-stock and crank the center into the hub to hold it between the centers. Yes, that is "turning between centers." Standard procedure is to use a lathe dog to secure the position of the workpiece in relation to the chuck (so it won't slip). We have nothing to secure the lathe dog to, and we are only taking off a few thousandths anyway. All you want to do is face the hub, so cut a few thousandths at a time and feed the tool across the face slowly. Too fast, too deep, or both can stop the hub from turning and put a groove in the chuck center.

If you have a solid dead center (no ball bearings) or a ball bearing center too small for the outer race you can chuck the little beggar up in a four-jaw. The whole set-up procedure is outlined in the Bell Auto-Airheart part of this story.

The outside of the rotor surface can be done in several ways. First, turn the disc face for a true surface. The rotor hub face can be trued in a three-jaw lathe by gripping the inside of the rotor. Dial indicate the disc face to true in chuck. Use a soft hammer or mallet to move rotor in chuck. When the indicator reads 0 all the way around the disc face, face the rotor hub with a tool bit. Only take off enough metal to clean the surface of high and low spots. You can also true the surface in a horizontal mill, vertical end mill, or surface grinder. Just clamp the disc to the table on the mill and make a clean-up pass. It would take a rather large surface grinder to handle the rotor but it is the easiest if it has a magnetic chuck.

To true the inside of the rotor hub, place the rotor in a three-jaw and dial indicate the disc face in. You will need a boring bar that is designed or set up for bottoming and facing, and long enough to go to the inner rotor hub face. Once again, just cut enough metal, a few thousandths at a time, to true the surface. Trueing the faces of the rotor hub and spindle hub are as important as surface grinding the brackets.

Herbert & Meeks '64 and later 'Vette disc to '49-59 Chevy pickup require two '53-54 Chevy drums. They have larger bearings and fit the pickup spindle. The difference between the '49-'54 passenger and '49-54 pickup spindle that concerns the adapter is the steering arm arrangement. The passenger steering arm bolts between the spindle and backing plate. The pickup steering arm bolts on the outside and spacers are used between the spindle and backing plate. These steering arms are not interchangeable from one to the other. Because of the difference in spindle flange spacing, Herbert & Meeks came up with a three-piece caliper bracket for the pickup.

The first piece is cut from 1/2-inch hot rolled steel. Measure and drill the four backing plate holes 7/16-inch on the top and 1/2-inch on the bottom. Torch or mill the center out so the spindle bolt can pass through and seat against the backing plate flange. The caliper will bolt on the back in a vertical position, so leave some metal to drill into.

Set the Chevy hub into the rotor as outlined in the I & J Chassis 'Vette disc to '49-54 Chevy spindle in this story. Assemble rotor unit on spindle to measure how far away the caliper will fit from the spindle. Make another bracket from 1/2-inch hot rolled plate that bolts to the caliper. With the caliper at its correct height and position, a portion of the caliper bracket overlaps the extra portion on the spindle bracket. There should be enough room to drill three equally spaced 1/2-inch holes into both brackets to locate the caliper in the correct position from the spindle bolt. To get the correct centering of the caliper over the rotor, a 3/16-inch spacer between the two brackets, the length of the brackets, with the three holes to match is needed. If the caliper does not sit over the rotor with full lining contact, back to the machine shop. It's gotta be right,

When it is right, surface grind or Blanchard grind the brackets, easy on the 3/16-inch spacer. Use socket head or grade 8 bolts to bolt the conversion together. The pickup front end must use 15-inch wheels to clear the caliper, mount and the tie rod end.

Our records show that the 10.7 inches tall Volvo rotor from the 142, 144, 145 and 185 coupe, station wagon, and four-door coupe from '67 to '70 can be adapted to the '49-54 Chevy spindle. Check with your Volvo dealer as to how far beyond '70 these brakes are made. For information refer to Volvo disc to early Ford spindle.

First, drive or press (we prefer press), the lug nuts out of the drum so you can get at the rivets to grind the heads off, Remove hub from drum and rivets from hub with a drift punch. Set up the hub in a four-jaw lathe chuck with enough of the flange circumference past the jaws for a dial indicator to rest on. Dial indicate the circumference and drum face of the flange to 0. Support the small bearing end with a ball bearing center and turn the diameter of the hub until it is true from the tip of the hub to the flange face. Also true the flange face. Leave a small radius at the flange/hub point intersect because a square shoulder is a weaker point and will fracture quicker than a round or concave shoulder. The hub can also be turned between centers as outlined in the Herbert. & Meek '49-54 Chevy spindle to 'Vette disc brake story in this article, Just use light cuts with this setup as there is no way to anchor the hub to the chuck.

So the rotor will slide easily on the hub flange, machine the hub diameter .010 from the tip toward the flange, leaving a shoulder for the Volvo rotor to locate on. Measure the larger diameter and machine the rotor hub locating hole out to .0005-inch over or slip fit. The set-up procedure to machine the rotor and hub is outlined in the '49-54 Chevy spindle to 'Vette disc changeover by Herbert & Meeks. Be sure to give the inside rotor locating hole a radius to match the hub.

When assembling the rotor to the hub use the same method as in the J & J Chassis 'Vette disc to '49-54 spindles. Place the assembled unit on the spindle and set the caliper on the rotor to measure for a caliper bracket that will hold the caliper in a vertical position at the front of the disc. Make a bracket as outlined in the J & J Chassis 'Vette disc to '49-54 Chevy spindle in this story. Spacers may be needed between the bracket and caliper, which is also outlined in the J & J Chassis conversion.

Assemble the unit with grade 8 or better bolts and lockwashers or lock-nuts after all the clearances have been double-checked for spacing and concentricity.

Hamilton Automotive Industries offers a kit for the large Volvo disc that includes the bracket, Volvo hubs, rotors, bearings and fasteners to '49-'54 Chevy spindles, Kit also contains a combination grease seal and spacer so all Volvo parts can be used. The Chevy spindle needs machine work on the inner bearing diameter, Hamilton will machine your Chevy spindles, or use his spindle exchange program, or buy the Chevy spindles outright in the kit. The lower steering arms have to be milled for clearance. Steering arms are available at extra cost. He can also supply dropped Chevy passenger lower steering arms. All he does it use the passenger upper half of the arm and the lower half of the pickup steering arm and weld them together.

 

For the custom builder, there are varied disc brake units manufactured for most applications. There are a number of manufacturer/dealers that carry a wide line of kits.

Mr. Roadster has a good assortment that he adds to from time to time so I thought I would drop by for the latest. Jay Roadster, owner, said that the manufacturers he buys from hadn't supplied him in months so he was going to manufacture his own.

His disc kits are for '37-'48 Ford and '49-54 Chevy spindles ready to install with Airheart calipers. The alloy hub is designed to mount a passenger car stock or custom five-lug rim. These kits are complete and bolt-ons, and recommended for use on heavier cars.

Other caliper plates are also available for this kit. There are plates for the single, double, and quick change caliper for the '37-'48 Ford spindle. The '49-54 Chevy mount is for single caliper only. He has other set-ups for the Jag front and rear brakes.

Jay's wire wheels are sold with or without the disc brake kit. The wire wheels come trued and laced, with chrome caps, built-in flange for mounting disc brakes if desired, and tires and tubes installed, Price includes wheel bearings and seals. They are available with either 16-inch by 300 (22-1/2-inch tall) or 18-inch by 300 (24-1/2-inch tall) tires. The hub will fit '37-'48 Ford, '49-54 Chevy, and '60-68 Econoline spindles. These wheels are designed for front end weight of up to 1000 pounds. The standard disc brake kit for these wheels includes two 10-inch by .160 discs, two steel caliper mounting plates, two spacer rings, two Airheart #150 single piston (pushes from one side) calipers and all necessary bolts and nuts. The Super disc brake kit includes two 11-13/16-inch diameter by .375-inch discs, two steel caliper mounting plates, two spacer rings, two Airheart #175-06 series calipers with dual pistons (pushes from both sides) and all necessary bolts and nuts. Write for catalog.

Total Performance has an excellent line also. They have the '62-67 Volvo small rotor disc brake adapter to '37-'48 Ford spindles with some machine work and full instructions. They also have a spindle exchange program. There is also the Corvette disc to '49-54 Chevy spindles adapter, lugs, and instructions. Another available adapter is to mount '86-67 Mustang discs to '37-'48 Ford spindles. There is a minimum amount of spindle machine work and adapter comes with complete instructions. Also new in their catalog is a disc brake kit to adapt any year Camaro and Chevelle disc brake to '49-54 Chevy spindles. Machine work on the spindle is required but instructions are included in the kit.

They have a disc brake kit that includes 500 series Airheart calipers, 356-T6 Aluminum hubs with outer bearing races and 1/2 -inch right hand studs installed, 3/8-inch steel discs, and caliper mounting brackets. These kits are available for all: Econoline, Corvair, Crosley, and Mustang plus Pre-'48 Ford, Willys and Anglia. These kits are also for '49-54 Chevy and up through '62 Corvette, and '55-58 Chevy.

TP has 18-inch wire wheels that come laced, trued, with chrome caps, tires and tubes installed to mount on your car. The hubs will fit early Ford spindles, '49-54 Chevy spindles and 60-68 Econoline spindles. These wheels can be ordered with or without the brake kit. The kit consists of #150 Airheart calipers, caliper shims, 10-inch x .160 thick steel disc, 4-inch x .400 thick alloy spacers, 4-5/16 x 1-inch bolts and nuts. Brackets for early Ford #150 calipers are extra. Write for catalogue.

Straight Away Engineering has a line of disc brake kits for Anglia, Ford, Willys, Mustang, Chevy, Econoline, Lincoln, Mercury, and three-quarter-ton Ford. Write for information.

Speedway Motors has their own disc brake kit that fits early Ford hubs and spindles. The kit comes with rotors that bolt on over Ford hubs and brackets that bolt to Ford spindles. The kit has dual piston (pushes from •both sides) Hurst Airheart calipers and all the necessary mounting hardware. Write for catalogue.

Hamilton Automotive Industries offers a disc brake kit that will fit 49-'54 Chevy hubs, early Ford hubs, and '65 or newer Corvair hubs. This kit uses the '69 and newer VW discs and calipers. Curt prefers the Meehanite VW disc over the steel discs because steel has a tendency to gum and has a higher expansion coefficient. The VW disc, when drilled for the Chevy bolt pattern, will bolt straight on the Chevy hub. Early Ford hubs must have the drum flange turned to diameter so it swill fit inside the VW disc and no more than a 5-inch lug pattern can be drilled. Curt Hamilton figures that by the time this story is published, he will have the 5-1/2-inch pattern available on the early Ford hub, He also offers a large Volvo disc to early Ford hub kit that requires the same machine work.

The disc and calipers are from '69 and newer VW 1500, 1600, 1302, and 13025. He has a kit of new parts which include rotors, number 3 calipers, machined early Ford hubs on exchange, other hubs outright if desired, caliper brackets, fasteners and a handful of shims to adjust the caliper position. His used parts kit consists of the same pieces except it has number 2 calipers. Number 3 calipers have larger pucks than the 2s and a wider racket hole spacing to accommodate the larger puck. The late model number 3 calipers will handle up to about 2800 pounds vehicle weight. All the rotors are the same and are a solid disc. The brake units will clear 13-inch custom aluminum rims. Curt will supply machining instructions for this conversion but there is a whole bunch of trick machine work that doesn't make it worthwhile to do it yourself. He does offer any lug pattern change on whatever hub you wish except 5-1 /2-inch on Chevy hubs. As a matter of fact, he will adapt any hub/spindle combination that you might have to the VW disc.

Hamilton makes his own adapter kit to mount a 3/8-inch by 10-inch Blanchard ground disc to the Halicraft spoked wheel. The hub adapter is one piece and uses no spacer. The calipers are the 175-08 Hurst Airheart 2 piston type (push from both sides). The adapter will bolt to the '37-41 Ford spindle, but the square corners of the backing plate flange will have to be clearanced on the '42-'48 Ford spindle. This kit has the adapters, calipers and brackets, discs, and aircraft fasteners.

Hamilton offers upper steering arms on all his conversions at extra cost. He also supplies an ample mount of different thickness shims for correct caliper to rotor adjustment in all his kits. Curt says that money motivates him to make a disc brake kit for any spindle/hub combination. Write for particulars.

This article has covered the most popular brake changeovers that we have reference to. By no means do we mean to say that you are limited to these conversions or manufacturers we mentioned as there are more. We have assembled a brake directory that should cover most custom needs. A letter or phone call to the dealer should answer your questions. Also, most manufacturers and dealers have a catalog. Remember, the brake system is the most important system on your car and your life rides on it! Spend on your brakes whatever you feel your life is worth.

 

BRAKE PROPORTIONING

When designing and selecting a braking system for your machine, there are things you gotta know. Locking up the rear brakes only produces a condition which results in a partial or complete loss of control. This condition is very unstable and the car could easily go into a spin. On the other hand, locking the front brakes only produces a stable condition in which the vehicle travels in a straight line. In this condition there is almost complete loss of steering control. If all four brakes are locked, it produces a condition which is fairly stable, resulting in the car traveling in a straight line.

It is safer to lock the front pair of brakes if we must lock a pair of wheels. Taking into consideration the vehicle weight transfer to the front wheels when braking, a rule of thumb front-rear braking percentage ratio has been formulated. A 60% front and 40% rear braking ratio is used in general with 65/35 distribution for competition and sports cars. This means that 60% of the braking is designed into the front brakes and the remaining 40% in the rear.

The 60/40 ratio is a compromise under ideal conditions. Not so ideal is mud, rain, or ice where the coefficient of friction between the tire and road are less than desired for maximum deceleration rates, and the front wheels will tend to lock up. The coefficient of kinetic friction (skidding tires) is always less than the coefficient of static friction (non-skidding tires). The maximum rate of deceleration is just before the wheels start to skid, and when they do, you lose about 25% of the stopping power. It's the grip of the tire on the road that actually determines how fast a car can stop, even though you can lock your brakes.

The problem of weight distribution and weight transfer during braking is very important. The braking force of a wheel is related to weight on that wheel. It is the ratio of the center of gravity height to the wheelbase length that determines how much weight is transferred to the front wheels during braking. Long wheelbase and low center of gravity tend to reduce dynamic (movable) weight transfer. If a brake system is not designed for this weight transfer, serious problems can result.

Various methods used to produce a higher braking percentage on the front end, but not necessarily limited to only these, include:

1. Use of larger wheel cylinders on front brakes than on rear.

2. Use of wider brake shoes in front than on rear.

3. Use of brake shoe material with higher coefficient of friction on front brakes than rear.

4. Use of a brake shoe actuating design which features servo action, such as the Bendix 2 shoe, single anchor, self centering type.

5. Use of smaller total diameter wheel in front or larger wheel in back, or combination of both.

6. Use of larger diameter brake drums on front than back.

7. Use of pressure proportioning valve between the front and rear brakes.

When disc brakes are installed on a front end with drum brakes on the rear we arrive at a new set of problems. There is no servo action in a disc brake which requires high hydraulic line pressure and heavy pedal pressure. Even with a proportioning valve, the distance between the brake pedal axis and the master cylinder pushrod pivot may have to be shortened to gain leverage for higher line pressure. Disc brakes lack instantaneous gripping at low speed and do not decelerate any faster than drum brakes. Their main advantage is that they are fade free, whereas a drum brake system will fall off in performance as brake fade sets in.

In spite of proper proportioning, brakes too small won't work satisfactorily. If the disc rotor is too small in diameter or the drum brake too small in total drum swept area, brake fade is unavoidable. Brake fade is caused by excessive heat retained in the brake system.

All brake systems must be large enough and have sufficient mass to absorb the heat generated in an emergency stop from high speed. It is impossible to dissipate the heat as fast as it is generated, but the system should be able to keep the drum temperature down within reason and dissipate enough heat between brake applications to avoid fade.

The idea behind drilling brake drums and backing plates is for air circulation and cooling, but it doesn't work too well. Drilling reduces a mass of metal and the heat is not conducted away from the interface, the line between the brake lining and the brake drum, as quickly as it normally would be. The holes will pick up sand and grit which accelerate brake wear appreciably. Brake efficiency will be increased and brake cooling accelerated by leaving the brakes undrilled.

Aluminum paint on brake drums does not accelerate heat transfer. The rate at which heat is dissipated from the brake drum depends on the heat emissivity characteristics of the brake drum surface. Rusted iron has the highest rate of heat emission. Aluminum paint acts as a highly-efficient heat insulator by reflecting the heat back into the drum. Do not paint brake drums for optimum efficiency. If you do, paint them black.

Difficulty arises when trying to figure a sufficient brake size necessary to avoid excessive heating because of many variables. Much of the work is trial and error. When selecting brakes, comparing total brake lining is not a good way to judge brake system efficiency. The total swept drum area is much better method of indicating braking effectiveness.

This is only meant as a reminder and guide line and barely touches the surface. Don't neglect to do your own research on the system you want to use and how to use it. No matter what you might think, the brakes are the most important system on your car. No matter how fast it goes, the car won't be worth much if you can't stop it.

 

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Outstanding... Exactly the data I needed for my Bell-Auto kit. Thanks Man!

 

Some of this is out of date (who would try to find vintage Volvo parts these days), but there's still some useful info....

 

I think there are better disc options today.

 

Great info, thanks.