I'm building a '29 closed cab model A pickup, no fenders, chopped 6", channeled 4". 383 stroker w/700R4, 8"Ford rear. My question is brake set-up, this is what I'm using and have so far: GM Metric calipers -- disc/disc Front 2 3/8" bore rear 2 1/8" bore 11" rotors 5.86:1 pedal ratio 7" single diaphram booster GM Corvette style master cylinder with 1 1/8" bore -- under the floor 2# residual valves front and rear Maybe a proportioning valve ( don't have it yet ) big & little tires, 24" front, 30" rear.
First you have to have a proportioning valve when you mix disc & drum brakes . Just curious why are you using power brakes ? Should stop fine on manual brakes with no problems . Where are you mounting the M/C ? Retro Jim
I dunno... I like to match components off a single donor myself BUT your asking the right questions and I hope someone helps you out. My only reason for posting is to mention that you need to be careful you get the correct GM calipers. SOME of the Metric front calipers require a "Quick takeup" style master cylinder as the caliper pistons retract more than normal to give "no drag". The No Drag Calipers had that special matching (ugly) Master cylinder to give a big push of fluid to the caliper piston to get it seated and then it reverts to normal ratio to keep the hydraulic pressure up. You cannot use a No Drag caliper with a normal master cylinder or the pedal will be extremely low! Something to watch for now...not as you try to "bleed" the problem away! All the best on your build!
I'm using a disc/disc set-up and not sure about a proportioning valve, M/C under the floor and booster because I want this one to stop! Also I do have 2# residual valves for front and rear. Looking for 8" Ford center section w/3:55 gears or close.
http://www.mpbrakes.com/index.cfm These people are pretty good at answering questions they state that disc to disc may need a combination valve.
It all sounds good but a proportioning valve wouldn't hurt. What are you gonna use for brake lights switch? lever type, or pressure.
Your pedal ratio is high for power assist. Generally, you want 3-4:1 for power, and 6-7:1 for manual. Running a manual ratio with power assist will result in VERY sensitive braking! I would aim for 4:1 with that large 1 1/8" master. I had a bad experience with a friend's single 7" booster. It went into "run out" or manual mode too early. In other words, it provided boost with light brake applications, but went manual with med-hard pedal efforts. The ZZ4 350 had ample and "checked" vacuum with no leaks. The problem was solved by switching to a tandem (dual) 7" booster. Adding an adjustable prop valve is a good idea, as most US disc/disc non-ABS vehicles have prop valves. Avoid the factory "fixed combo valves" that seem to be a fad now. As has been noted, some GM calipers had high piston seal retraction requiring a "fast fill" stepped-bore master cylinder. I would make sure your calipers do not require this master. JMO.
Definately want a prop valve. I used one with my disc/disc set up and it allowed me to dial in the rear brakes to lock up first and I maintained steering control. Ideally you want all four wheels to lock up at the same time and since your weight bias is different front to rear, you need the prop valve to adjust.
I hope you meant front brakes to lock up first, as you do NOT want the rears to lock before the fronts.
There's lot's of answers on various components here: http://www.how-to-build-hotrods.com/brake-system.html I agree with Hackerbilt; It's generally advisable to go with parts designed for the same car...
Hackerbilt, Your comments on the two types of GM meteric calipers is disconcerting, first heard for me. How can we be sure what type we have, or will be purchasing in the future? For instance, those calipers we might get from a racing parts place versus over the counter at the local auto parts store? Can we ident them from particular auto makes and models? Or? Likewise, MC types to match? Thanx for the info, Gary
The idea of a proportioning valve was to match the brakes ability to stop over a varying range of conditions. The relationship of front to rear brake balance is not a static relationship because of weight transfer. For instance, at low speeds (low brake force - let's say in wet road conditions) little or no weight transfer is experienced and therefore the "preset" balance of let's say 50/50 may be optimal. At higher speeds with better road conditions weight transfer occurs and the front tires due to additional loading can now support additional braking. Conversely the weight that shifted to the front was also removed from the rear reducing the rear's ability to brake which ultimately shifts the ideal braking balance closer some other relationship - usually somewhere around the 70/30 number we hear so much about. You can "get by" without a proportioning valve - as many have done it, but it then becomes a compromise of brake balance - you pick ONE relationship (ratio) and are "off" at all other conditions. If you can eliminate the weight transfer - then you can eliminate the need for the proportioning valve (not gonna happen). The use of Proportional valves assumes you are wanting to optimize your brakes. If "good enough" is your goal - well then that's a different kettle of fish. For me - I prefer a parachute. ;-)
Do a HAMB search or an internet search to get loads of this info to come up. Apparently the only way to tell exactly what you have is to examine the piston! The early Metrics up to around 82(?) didn't have the low drag piston but some of the rebuilders lump them all in to the same part # anyway. HOPEFULLY those rebuilders will use the regular drag piston in all their calipers as that way one size will fit all (in matched sets!)...but you never know what might mean a "rebuild" to any particular rebuild shop! I don't think I'd want to mix and match them on the same axle, but I'm sure there are cars on the street like it right now! fitzee ran into the same problem on a project car and just changed out the regular master to the quick takeup style. Went from no pedal to full pedal!
You don't need a porportioning valve until you need one. IF you need one use an adjustable one... When you set up your lines have the one to the rear with a inline connector near the master where you can tap in the valve. Your pedal ratio is high.. pedal response will be quick.....good on some cars.....What cam / intake system are you running...you may need a vacuum "can" reservoir to provide proper vacuum to the booster. The "pull-back" calipers are used on the rear...they are fun to work with. IF you are using them you must use the parking back system from that car...and you must operate the parking brake to keep the piston in the proper location.....They are VERY hard to bleed...I put a set on a Camaro and we tried two types of pressure bleeders and three styles of hand bleeding before we figured out what we were doing wrong.....the parking brake was out of adjustment...
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