I was reading Harrison's post/thread about installing a dropped axle in his '38. I remembered giving him some tips on what to do. Here's a tech article I wrote for another website a couple of years ago. They considered it good enough to be included in their Old Ford Tech Library. Here it is: <CENTER>Dropped Axles & Stuff</CENTER> This will be a little lengthy, but I thought I'd share what technical information I've learned doing five dropped axle installations along with the reversed arch spring thing on my own cars (1936 thru 1948). SPRING: 1) If you try to lower the front end a significant amount by just reversing the arch of the front spring and removing leaves, you can have a problem with the stock radius rods hitting the frame rails, especially on the stock steering box mounting bracket (it can be heated and bent for more clearance with no saftey issues). With this solution you've lowered the front end but have sacrificed suspension travel. You can alter the length of the axle rubber bump stops to limit suspension travel to prevent the radius rods from hitting the frame but it will "bottom out when hitting a significant bump. 2) An advantage of a thinner spring "package" is you can shim between the frame and spring to get "your" desired ride height or "look". 3) Another problem with this method a reduction in shock absorber travel. Lever action shocks will have the arms pointed "uphill" unless you shorten the shock links. Make sure tube shocks aren't bottoming out in their travel. I've had to go with shorter shocks to correct this problem. DROPPED AXLES: 1) I've used Bell, Chassis Engineering, Magnum and Mor-Drop I-beam axles. All are OK depending upon what you're doing. Most importantly with a dropped axle you retain most of your suspension travel. Depending upon the amount of "drop" you want, you may not have to reverse the arch of the front main leaf. Removal of a few spring leaves might be all that's needed, primarily to improve ride comfort. Remember to install shim(s) of equal thickness to what's taken out so your stock U-bolts will clamp the spring tight in the crossmember. 2) The Magnum and Mor-Drop(a stock axle with ends heated and reformed) have stock perch pin (or radius rod mount) spacing. If you're using the stock transmission or just want to retain the stock radius rod mount on the frame, this is the way to go. Why? Because the stock radius rods can stay the same length. Looking at the radius rods as a triangle, none of the dimensions have to be changed. The axle is "almost" a bolt in replacement. I even use the stock lever action shocks and sway bar under my '40 Coupe. 3) Bell and Chassis Engineering(CE) have a reduced perch pin spacing. This changes the dimensions of the radius rod triangle and moves the pivot ball location to the rear of the car. If you're doing an engine and later model transmission swap, plan on using a radius rod split kit with these axles. They work great! Also, plan on a shorter spring main leaf because the distance has been reduced between the shackle pivots. STEERING ARMS: 1) I have heated and bent steering arms, but don't like to because it can mess up the Ackerman, other geometry and cause safety issues. 2) I like to use the dropped steering arms made by each individual axle manufacturer. You have to cut the stock steering arms off the spindles to do this. But spindles are plentiful because all the hi-tech street rodders are installing Mustang II "stuff" under their cars and selling off the "good old stuff". So, if you want to back to original some day, pick up some spares at the swap meet. 3) When you are cutting off the steering arms I prefer to use a pair of later '46-'48 square back spindles, if you have access to them. #1) The later spindles use a longer kingpin, which I like. #2)The later right front spindle has the tie rod entering from the bottom and the drag link entering from the top. The round backs have both entering from the bottom. So, if I'm going to destroy a pair of spindles for this swap, I opt to use the square backs. My personal preference. TIE ROD and DRAG LINK: 1) I think the Magnum axle is about 1" shorter from king pin to king pin. I think the CE and Bell are even narrower. This tucks the rims and tires inside a little to gain needed tire to fender clearance when turning. 2) Because I'm pretty frugal, I use the stock tie rod and drag link with the Magnum axle swap. Because the kingpin spacing is reduced you have to shorten the tie rod an equal amount. I cut off the right hand threaded end of the tie rod and rethread with a right hand thread tap I bought from Travers Supply. I reslit the tie rod with a thick hacksaw blade or zizz wheel and reinstall the clamping collar and tie rod end. The tap is special, you won't get it at Lowes or Home Depot! Cost about $10. 3) Because you only have to shorten the drag link about 1/2", you can usually get that much distance out of the adjusting sleeve. This is using a stock steering box. SHOCK ABSORBERS: As I mentioned before, make sure the shocks have enough travel so they don't "bottom out". I've used both lever action and tube shocks. It's amazing how good the old lever action shocks work! TIRES: The best "hot rod look" I've obtained is with a 165/80R15 (26.5" diameter) on a 5" wide rim on the front and a P235/75R15 (29" diameter) on a 6" or 7" rim on the rear. If you're using a stock spring in the rear you'll probably only be able to use a 6" rim with close to original back spacing. Otherwise, the rim will contact the spring shackle mount. Also, you'll have to heat and bend the stock shock arms toward the frame, otherwise they'll hit the tire inner sidewall. ALIGNMENT: Assuming we all know what the terms mean. I run 1/16" to 1/8" toe in with radial tires. Camber on these replacement axles has been consistently correct, about 1 - 1.5 degrees positive. After dropping the front end down, usually I have to adjust the caster back to 5 - 7 degrees positive. This "stuff" is not rocket science and can be done in your "well" equipped home garage. I'll save the procedure for another day if someone wants to know. OVERALL: For me, the dropped axle front end is the best way to go. My cars with this set-up handle great, track down the road straight and have plenty of ride comfort. My '40 pick-up with only the spring thing done works OK, but lacks the ride comfort of the dropped axle cars. It's slated for an axle change in the future! I've owned old Fords with Mustang II independent front ends and didn't like 'em for a variety of reasons. Sometime in the future I envision hot rod parts suppliers selling kits to convert Mustang II front end old Fords back to straight front axles!!!! Modifieddriver Positive and/or negative comments are welcomed .
Modifieddriver:Thanks for the very good article. I dropped the front of my 40 ford by using the 4 inch Magnum dropped axle and dropped steering arms along with a posie reversed eye spring. Front tires are 5:60 x 15. Rears are 7:60 x 15. Toe in is 1/16 in. Do I need to adjust the camber and if so how is it done? Thanx
Thanks for the positive comments. I'll do another thread on bending axles to adjust camber. It's a "piece of cake" to do in your home workshop.
This information was a blessing while I did the deed on my '38. It should really be put in the Tech-O-Matic for future reference. One thing I'd agrue though - those 15" tires. It don't get any better than this... JH
If ya' need help, send me a PM. I may do a reversed arch/rebuilding spring tech and a camber adjusting tech. Besides Harrison, I have had several folks asking for tech info.
This is an awesome post! I am going thru this right now and I'm having major clearance problems with the spindle arms hitting the drop axle. This explained everything plain and clear that I need to fix the problem. Viva la H.A.M.B.!
I hear that if your not going to split the bones like on a 1936 . Then your going to need a new set of bones?? I hear 1940's 4" drop need a 1935's what would a 1936 need
Don't think what you said is correct. From what I've been told, ya' know how that goes , the narrower perch pin spacing of '35-'36 radius rods may work with a Super Bell axle so ya' don't have to use the split kit. '37 they went with wider spacing between perch pins, but the king pin spacing is narrower. Then there's the thickness of the beam of the axle that's different. You'd have to do some measuring to figure that out.
There was a tech in street rodder a while back talikng about using a set of 35 bones on a 1940 ford drop. It was to relocate the axle in the correct position. My Buddy did this on his 39 and it worked great but finding a 35 set of bones is not so east these days not sure what were going to do on the 36 yet
Continentaljohn, I have a dropped A axle.I was wondering if you used newer spindles and dropped steering arms on the A tudor you had. Did you just lower the stock A lower arms and use stock spindles tie rod/drag link. Any advise welcomed.
Why would you want positive camber (tire leaned out at the top)? That would just promote rolling the sidewall over, and with the straight axle, it's not like you're going to have a steep camber gain curve like you would with a IFS. With a ten degree kingpin angle, and zero caster, at 20 degs of turn angle, you'll have ~2.25 degs of positive camber ('cause the axle is straight up and down, but the kingpin boss on the spindle is still canted at ten degrees), no matter which way the tire turns. If you could turn the wheels to 90 degs, you'd end up with 10 degs of positive camber, but they obviously won't go that far with all the bits attached. Once you roll say 5 degs of positive caster into the axle (top of spindle leans towards back of car), then you have less positive camber when you turn in, and more positive camber when you turn out. At 20 degs of turn angle you'll still get the 2.25 degs of positive camber from the kingpin inclination, but the caster adds in 1.1 degs of negative camber, so your total camber at 20 degs of turn in will be +1.15 degs, and your total camber at 20 degs of turn out will be +3.35 degs. That's with no static camber at all. In fact, I'm not seeing how static camber would do you any good, 'cause once the wheel turns, the static camber goes away ('cause it's only present while the spindle snout is in-plane with the axle). Am I missing something about what a solid axle likes, alignment wise? 'Cause from here it looks like a recipe for wearing the letters off a sidewall in a big hurry.
Why would you want positive camber (tire leaned out at the top)?(Quote) If memory serves me right, camber settings toward the + were a result of compansating for "road crown". Some manuals went so far as to specify different camber settings for the left and right side. On a flat surface, the camber setting should be able to be set at 0 degrees. An example might be how we used to set - camber, in varying degrees left and right side, for a race car turning left on a banked track. That's it, my brain guage shows empty.
Hmmm . . . Road crown, eh? How does camber really effect straight line handling? I would say it pretty much doesn't. Perhaps they meant that it was supposed to put the tire flat on a highly crowned surface? Like to stop edge wear if the road had a lot of crown? I wonder how much crown would be required to need a degree of positive camber to cancel it out. I'll have to do some drawing to figure that one out. Hmm . . . . Quite Perplexing. In our circle burners we used to run upwards of six degrees of negative camber in the right front, and something like three and a half degrees of positive camber in the left front. We staggered the caster too, to help it want to turn left (but not a lot, maybe a degree or so, 'cause on the dirt you turn right as much or more than you turn left). I'm just wondering about the best way to set up a straight axle to make the thing work like it ought to. You need at least two or three degrees of negative camber when you turn in, to make up for the sidewall deflection as you load the tire, but as far as I can tell, the stock setup will have about that much in the wrong direction (meaning positive camber where we need negative camber). Caster helps to a certain extent, but if you use too much, you get caster shake (and a very squirrelly car when going in reverse to boot). I dunno. Static camber would seem to be no help for turn in, and I'd not run more than six degrees of positive caster, so that still leaves us with the need for about four more degrees of negative camber at turn in. I'm gonna have to ponder this one some more and report back when/if I figure anything out. I think I'm going to model it in CAD and see what's really happening. If I go that route, I'll bring pictures when I come back.
I'm gonna have to ponder this one some more and report back when/if I figure anything out. I think I'm going to model it in CAD and see what's really happening. If I go that route, I'll bring pictures when I come back. (quote).... Good idea..My brain is cramping here, but I would suggest you model both A-frame and beam axle geometry. A lot of our traditional rods are riding on front end geometry that was a compromise for drivability on very poor roads and at speeds far below our freeway speeds of today. Good luck..look forward to your discoveries<!-- / message --><!-- sig --> __________________
Fearless Fast Frankie Four Fingers, You are a god! Great write up for sure. It makes me want to get my ass working on my "A". Now where is the tech article on the differences between early ford drums?? BloodyKnuckles
Well, I ran my model tonight, and posted the results in this thread: http://www.jalopyjournal.com/forum/showthread.php?p=3126100#post3126100 My findings pretty much bore out what I'd suspected to begin with. I still don't know why positive static camber was part of the standard alignment specs back in the day though. All search efforts returned bumpkis both here and via search engine. Alas, but it seems that my Google-Fu is weak.
Nice work..Think you are on the money..try typing "Camber Theory" on google. It'll show you grahically what I meant about road crown.
The only article that turned up was one written about large trucks in the UK. It seems they align the big trucks much like you would a backwards circle track car, 'cause they spend a lot of time running around in clockwise circles (called roundabouts ). I'd be interested to find out whether US truck fleets align their trucks in the same way. Regardless though, what big trucks need will be greatly exaggerated from what a light car needs. To put it another way, changes in alignment make a bigger difference in feel and tire wear the heavier the vehicle gets. The problem I have with preferentially aligning anything (be it car or big truck) is that you need to know the geometry of the road surface to make the correct adjustments. If you can't know the exact road geometry, you gotta look at the generalized case (an average guess, if you will) and align based on that. However, there are no two roads in the US that are similar enough that you can make that kind of generalization and have it be meaningful in any way. I've worked on road projects, and the variables change from place to place, mile to mile. It's nowhere near consistent enough to try and cancel out road crown with camber, caster stagger, or toe. The road geometry just changes too much from place to place for that to work the way it's supposed to.
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