Technical Brake issues.

I have been trying to track down a problem with my brakes. (Discs front, drums rear. All mid 80's GM) I will bleed all brakes thoroughly but after a week the pedal goes soft and I can bleed more air out of the fronts. This goes on and on. There is no visual signs of a leak. Master is under the floor and line has the brake light switch and a check valve in it. I am in the process of re doing the lines and replacing the flex lines to the calipers. I had disconnected the lines from the master and noticed the passenger wheel did not spin freely. First thought was a bad bearing but when I disconnected the flex line at the caliper and the fluid drained out, the wheel released and spun free. Is there possibly a problem with caliper or why would it stick until the fluid was drained. Any help or advice is appreciated.

 

Brake pedal not returning all the way?

 

Verify your pedal to pushrod length is properly adjusted.

 

Could have a seized caliper or collapsed flex line cause the fluid to boil causing air in the system.

 

Residual valve in the rears? Lack of one, or bad one, could cause air to enter that portion of the system when the cylinders retract.

 

problem with c3 corvettes 4 pot calipers seals didn't leak at first but let air back in the system.spongy brakes were the end result.could be a runout on a disc

 

I have checked the push rod adjustment and confirmed master piston is returning to the stop position. There are residual valves both front and rear, as well as a portioning valve in the rear. Master was swapped out to a Wilwood after suspecting the Ford one was bad. Both front calipers have also been changed. I'm in the process of swapping the rubber front flex lines fo stainless braided hoses.

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The air always is in the fronts. I have always been under the impression that the front and rear are two completely different sections which leads me to believe my problem must be in the front half. Am I wrong in thinking this????

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Has the proportional valve been blead? That was an issue for me.

 

They are 2 separate systems. You may find the "stuck" problem when you change out the rubber hoses especially if their old and collapsed on the inside.

 

Is this a manual or boosted setup?

 

if there is no leaks meaning you are not losing fluid, most likely it is a bad m/c. the m/c is by passing the front brake section. Tom

 

Make sure the front end is below the MC when bleeding meaning if on stands and it is level or raised it will cause pressure to resist and when lowered down go soft soon after.

 

I'm betting the "air" problem is a master cylinder issue. Its unfortunate, but these days, something being new does not necessarily mean its good. Gene