Thread: Brake Nightmare

Tweet

For months I have been trying to get brakes on my 31 Ford Sedan delivery. I have replaced everything with new parts. I have disc brakes on the front with GM calipers a 2lb residual and new lines.I just replaced the master cylinder with a new corvette style and a new combination valve and 7" booster. I have new lines running to GM calipers on the rear with a 2lb residual also. They are the regular style calipers not the small metric ones.I have bled the brakes until I'm bleeding and can't get a pedal. I checked pedal ratio and it's about 6.1. I get some resistance until I open the front caliper. One push of the pedal and everything goes away. Pedal can be pushed to the floor with my finger. I spent hours bleeding the master and lines and nothing. I have asked you guys before on this problem and wound up taking everything apart and using two single master cylinders from Wilwood and got a pedal but wouldn't stop at 60MPH at all at 40 it would stop just barely. So I figured if I buy a whole set up matched and tried it that would do it. Well, nothing I have done has given me brakes. I have never had a problem before when doing brakes. I have built 4 cars and this is driving me nuts. It has to be something simple I'm over looking. Please if anyone has any ideas I need help! The rear disc brakes are a bolt on kit. That I purchased. Thank you!!

did you bench bleed the master cylinder???

Do you have the calipers mixed up? Bleeder to the high point of caliper? It seams as you still have air in the lines some place. I would start at the master with pressure on the pedal crack the front line open and see if you get air and work your way at every fitting down to the calipers. Also make shure that the rod inside from the booster to the master is the right length.

Yes did everything by the book. Went so far as to make sure with master was level with a level. Blocked off all four ports and bled until no bubbles came out. Now I have a slight pedal until I start the car. With the booster hose hooked up the pedal goes away and you can push the pedal to the floor with your finger.

Sounds to me like the piston is sticking in the master cylinder,happens to us all the time when bleeding brakes at the shop. Try whooping the master with a hammer and try to bleed again,but do not go all the way to the floor with the pedal....

Yes the calipers are with bleeders up. How do you know if that rod is adjusted right? I tried to measure throw to see if rod was pushing piston all the way in.

I will try banging to see if master cylinder piston is sticking. Right now I'd like to take a hammer to the whole car!!! Thanks

unbolt the master from the booster. Pull the rod out of the booster and place inside the master. Mark the rod with a marker at the flange of the master. put rod back in the booster and see if the mark lines up with mounting plate of the booster.

On our midgets & sprint cars,it's impossible to bleed the brakes without removing the calipers one at a time,inserting a block of wood between the pads,and holding the caliper as high as possible with the bleeder straight up.
Just a thought as I'm pretty sure your masters under the floor.

Thanks guys I will check the pin and try the caliper removal and hold it up. First thing in the morning. I need to just walk away for now or I might do something I might regret. ( like beat it with a sledge hammer)Thanks again!!

RESIDUAL PRESSURE VALVES (RPV)
Residual pressure valves were used at the OE level until 1972. They were nothing more than a “duck billed” rubber valve in the outlet ports of the master cylinder. Their purpose was to slow down the violent surge backwards through the hydraulic system caused by the drum brake return springs. This surge would cause the cup lips inside of the wheel cylinders to distort and when the cup lips distorted, they would “take air”.

OE solved this problem by using “expander plates” attached to the ends of the spring inside of the wheel cylinder. These plates held the cup lips tightly against the inside of the cylinder bore and would not let the cup lips distort. Around mid ’73, Raybestos Manhattan in cooperation with Gibson Corp. invented a cone shaped spring with each end of the spring spirals cone shaped to fi t the inside of the cup lips. This eliminated the snap on plates that could come loose and score the inside of the wheel cylinder. The expander plates and the cone shaped spring ELIMINATED the use of RPVs at the OE level.

Some aftermarket brake suppliers would have you believe that the RPVs they sell will stop siphoning of the brake fl uid when the master cylinder is lower than the calipers and/or wheel cylinders. In order for a liquid to “siphon” one end of the tube or hose MUST be open to the atmosphere. In the case of a closed brake system, this is not possible.

One other thing needs to be said about RPVs!! If you buy a rebuilt master cylinder for your project, there is a possibility that it could be equipped with the duck billed valves (rpv) from the rebuilder. This is because many master cylinder applications use the same casting. If you install a rebuilt cylinder (which I strongly discourage) be sure to check the outlet port of the master cylinder on the disc side of the system. If you leave the rpv inside the port on a disc equipped car, it will overheat the caliper, pads, and rotors and could cause a premature lockup problem. If it was me I would get rid of them 2lb valves, I did that on mine and all my problems went away.

Thanks, I might try that. I'm up for anything that will work. I hope!!

are you sure the MC piston is not moving too far in the MC when you depress the pedal? Check that out also.

I've heard that it's a good idea to put a block of wood under the brake pedal when bleeding the brakes: reduces the piston movement.

OK, how do I know if the piston is going to far? How much travel is needed?Tried gravity bleeding didn't work couldn't get lines over the axle lower than master cylinder. Even took rear wheels off and set rear on the ground and jacked the front up. Bought a small brake vac kit that didn't work. Thanks!!