Rear Brake Issue

[RdstrRod]

I'm having a difficult (impossible?) time getting my rear brakes to work. 8.8" solid rear axle with Mustang GT discs. Stainless brake lines leading up to the 5/8" Wilwood rear master cylinder. Front brakes with the 3/4" master cylinder seem to work OK. No leaks anywhere. Numerous times we've bled the rear master cylinder, the calipers, and all the junctions in between. We've even taken the calipers off the rotors in order to get the bleeder valve above the brake hoses. The pedal remains soft and the rear wheels spin freely. I can, however, pump the pedal, get good feel, and get both front & rear brakes to hold. After that, it's back to the soft pedal again and no rear brakes. It's acting as if there is still air in the rear system somewhere, but we're not getting anything out when we bleed them. Any suggestions as to what's going on?
TIA, Rod

[edwardb]

Sounds like air still in the system. Did you bench bleed the master cylinder(s)? Means removing the brake line from the master cylinder and running a temp line back into the reservoir. Then pump the brakes until you get solid fluid with no air. Then re-attach the brake lines and bleed again. You might have air in the master cylinder(s) that can't escape.

[rcotner]

I had lots of problems bleeding my brakes until I was properly trained in the best method for doing it. It takes two people and a fair amount of time. I don't want to presume you don't know what you are doing, so please forgive me but this link shows the method I used. It worked well.

http://www.dummies.com/how-to/content/how-to-bleed-your-brakes.html

[RdstrRod]

We've bench bled, vacuum bled, pressure bled, right-side-up bled, and upside down bled very connection from (& including the rear master) all the way back to (& including) the rear brake calipers. We've pumped more than 2 quarts of brake fluid through the system to no avail. No air bubbles and yet no rear brakes unless… I pump the hell out of the brake pedal. Even though it appears to be pushing fluid, I'm now suspecting a faulty master cylinder and have contacted Wilwood's technical assistance. Still waiting for an answer from them.




Sounds like air still in the system. Did you bench bleed the master cylinder(s)? Means removing the brake line from the master cylinder and running a temp line back into the reservoir. Then pump the brakes until you get solid fluid with no air. Then re-attach the brake lines and bleed again. You might have air in the master cylinder(s) that can't escape.

[rich grsc]

I'm having a difficult (impossible?) time getting my rear brakes to work. 8.8" solid rear axle with Mustang GT discs. Stainless brake lines leading up to the 5/8" Wilwood rear master cylinder. Front brakes with the 3/4" master cylinder seem to work OK. No leaks anywhere. Numerous times we've bled the rear master cylinder, the calipers, and all the junctions in between. We've even taken the calipers off the rotors in order to get the bleeder valve above the brake hoses. The pedal remains soft and the rear wheels spin freely. I can, however, pump the pedal, get good feel, and get both front & rear brakes to hold. After that, it's back to the soft pedal again and no rear brakes. It's acting as if there is still air in the rear system somewhere, but we're not getting anything out when we bleed them. Any suggestions as to what's going on?
TIA, Rod

That sounds like you may have the calipers on the wrong sides? Have you adjusted the caliper pistons out so that you have no free play between the pads and rotors? Rear calipers need to be turned to move the pistons out

[CHOTIS BILL]

I had a similar issue. In the garage everything was fine for weeks at a time but tow to a race and there was air in the line. It turned out to be a bad caliper seal and a rebuild fixed the problem. It could also be a bad master cylinder sucking in some air.

Just a guess,

Bill Lomenick

[edwardb]

Needless to say, it shouldn't be this hard. Really seems like something isn't right, and pouring quarts of brake fluid through it isn't going to solve it. This may be totally random, but I had trouble bleeding the rear brakes of my Mk4. It seemed to bleed pretty normally, but no amount of pumping would give a hard pedal or brake action. So in that respect was a little different than yours. I too thought defective parts, but since all was brand new seemed a little unlikely. The problem turned out to be the wrong length pushrod on the MC, and the MC was never returning all the way back. Therefore the valving was all messed up. Something to look at with yours? Is the MC returning all the way back when off the pedal?

[RdstrRod]

Many thanks to all who have responded with thoughts & suggestions to my dilemma. Today we went at it again. Verified the master cylinder was indeed functioning. Then pressure bled the system again. Still a soft pedal and no rear brakes unless I pumped the pedal several times. There had to be air in there somewhere. So, off come the calipers again. We had tried a few times previously to rotate the caliper to get the bleeder valve above the highest part of the caliper. This time, however, we held the caliper as high as the brake hose would allow, bled it again, and got a whole bunch of air out of the passenger side. Oh Happy Day! I now have a firm pedal and both front & rear brakes are working properly. The only thing I can think of is there was air trapped in the crossover tube to the passenger side and it was finally able to get out when we elevated the caliper above it????
And now for some wiring fun…..