Well, I've done complete brake systems for years but I'm dealing with an issue on the '32 while switching out from drum to disc. Using a Wilwood four piston race brake setup(new)on the front with stock Ford drum rears. Ford style disc/drum master cylinder(new) and discs are plumbed to the large reservoir with an inline 2# residual valve. Pedal is spring loaded up with 1/2" free travel. Rears have an adjustable proportioning valve inline. The brakes bleed fine and pedal is good but the discs do not release fully and are definitely too tight to drive without overheating . I removed the residual valve but no change. The lines were blown thru with air pressure to clear them of old fluid before the new parts were bled. I can crack the line at the calipers (either side), the master cylinder, any line connection or brake hose and the pressure releases allowing the rotors to freewheel. My gut feeling is the master cylinder is not accepting the fluid back into the reservoir. Any other ideas I'm overlooking?
Could your master cylinder push rod be to long or misadjusted and not letting the reservoir pistons release all the way.. Hope I'm explaining that correctly...
I assume you changed the front hoses when you did the change over. I have had this acure when the old hoses have become restricted with age. My thoughts are that as you say the master is not bleeding off the calipers when the brakes are released. Maybe see if you bleed down the level of brake fluid in the master for the front brakes so there is room so to speak for more fluid to bleed back. Four piston calipers can displace a lot of fluid as appose to single or dual. Just some thoughts , Brake conversions can be a bitch! Even when you order a complete kit front and rear with what is suppose to be matching components. Scrape metal 48 has a good suggestion too. Good luck Larry
Hey Milo. Nope. As I explained the pedal/rod has 1/2" freeplay. I have made that mistake before. Lol. But that's what I'm looking for. Ideas that I have missed. Bet it's something simple I've overlooked. Tired of bleeding brakes.
Thanks Larry . New braided hoses and I've released the fluid in multiple connection points to eliminate collapsed hoses, pinched brake lines and plugged tee fittings. The master cylinder reservoir level is down 1/2". I'm stumped.
Apply the brakes. Then open the front bleeder without moving vehicle. If fluid shoots out the problem is either brake hose or master cylinder. How tight are wheel bearings? Might try loosening them one tooth on he nut.
Do you have a brake booster installed? Most brake boosters have an adjustable rod between the booster and the master that can apply too much pressure on the master, even if there is free play between the pedal and the booster. 1/4 turn in either direction on that adjuster rod between the master and the booster makes a huge difference in the master cylinder performance. Gene
Are any of the brake lines near the exhaust manifolds or tailpipes? The guy who originally put together my '63 Chevy "late-modeled" the truck using Square Body pickup parts, unfortunately in the build he tucked the brake proportioning valve inside the driver's side frame rail just below the steering column. After a short drive the heat from the exhaust manifold would cause the brake fluid to expand locking up the front disks, solution was to move the proportioning valve to under the radiator. Best of luck with your project.
If you do have a booster; a quick check is to loosen the master to bolts and slip body shims in place. If the calipers release now, you know it is the booster push rod adjustment.
Guess I didn't state. Manual brakes. The rod is not pressing on the master cylinder at rest position. After applying brakes, I can crack the caliper bleeder on either caliper and the brakes free upon both sides until the pedal is depressed again.
Is the m/c mounted above or below the calipers and wheel cylinders? Is it possible that the front and rear brake pipes need to be reversed at the m/c? Could there be a residual valve already installed in the m/c where you don't need one?
When I did a disc swap on my 50 Plymouth I had the exact problem you speak of. Hours of head scratching and I couldn’t figure it out. I pulled the master cylinder out and realized the C-clip in the back that holds the piston in was bent and holding the piston down a fraction of an inch. I replaced the clip and the problem was instantly fixed. Sent from my iPhone using The H.A.M.B. mobile app
The pedal has 1/2” free play? Or the pushrod does? That’d be a lot of free play between the rod and the m/c piston. Sent from my iPad using The H.A.M.B. mobile app
If we assume the typical manual brake pedal ratio of 6:1 that is only .083 p/r to piston clearance. Not terribly excessive but it could be tightened up a touch.
The pedal freeplay is excessive for elimination/test purposes only. The master cylinder is below the calipers hence the initial 2# inline residual valve which has been removed for test purposes also. I've plumbed the lines to the correct reservoirs. Large reservoir is the disc brake side. Keep the ideas coming. I'm checking them off as we go. Thanks guys.
it sure sounds like youve proven the problem is with the master cylinder. replace repair or rebuild the part would be the next step on the trouble shooting chart. should you care to do more investigations, there are residual valves within the master cylinder ports for drum brakes and not beyond the realm of possibility that one of them buggers could be in there where it don't belong. new masters are bad out of the box way to often too. little piece of crap the right shape in the master can cause you troubles too.
I have had Wilwoods that came with special washers that you can space out the calipers with.......................................
The master cylinder is new but that's no guarantee it's right. I'll replace it and see what happens . Will post the results.
this may be a longshot, when I got my 32 it came with Wildwood front disc set up and was having the same problem you are having and found out someone used the wrong rotors that were to thick and finally burned up my caliper and had to buy all new $$$
If you can release the pressure by loosening the line at the master cylinder it would appear you eliminate everything but the master cylinder.
If after eliminating the RPI you still have pressure that spurts fluid when you open the bleed at the Caliper then more than likely you have a built in check valve in the master outlet. Look in and see, it can be pulled out easily. Ralphie
The washers are to center the caliper over the rotor since they are a fixed caliper with pistons on both sides. The seal in the caliper is what returns the piston, it’s already been said but the master is holding pressure, the likely cause is the pushrod is adjusted wrong keeping the vent port covered which will cause this. Apparently he has ruled this out so if he cracks the line right at the master and the brakes release then change the master. Or....take it apart and see why it doesn’t work. Sent from my iPhone using H.A.M.B.
^^^^^^^^^^We said the same thing except you used a better word! "centered"^^^^^^^^^ This is assuming the OP has ruled out M/C & everything in between..................
57 fargo may have the answer. If their not floating calipers then the centering is very critical. You may have contact on one side or the other of the rotor.
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