Rear disk brake problem question

[fastom]

I have a rear disk brake system that I had a problem but I think I solved it. The rear brakes were locked up after I bled the system. I couldn't figure out why! I decided I would crack a bleeder and see if they would release. Fluid came out, no air, and now they seem to be working well.

My question is, what the h*&^ could I had done wrong to begin with?

The calipers are the Cadillac type with the E-brake built in.

[Hart_Rod]

Do you have the correct proportioning valve on the master cylinder?

[fastom]

I ordered the disk-disk proportioning valve, so I hope it's right.

Will the other proportioning valve hold pressure on the rear brakes?

[Hart_Rod]

Originally Posted by fastom

I ordered the disk-disk proportioning valve, so I hope it's right.

Will the other proportioning valve hold pressure on the rear brakes?

Yes. A drum set up has about 8 lbs of residual pressure, while the disc has only 2 lbs. You may also want to check and make sure the e-brake spring holding not holding any pressure when not engaged.

[fastom]

Hart-Rod, thank you for the help.

I have double checked the e-brake setup and I have found no problems with it. Is it possible to know by looking at the proportioning which one it is?

Thanks again for the help.

[Hart_Rod]

Originally Posted by fastom

Hart-Rod, thank you for the help.

I have double checked the e-brake setup and I have found no problems with it. Is it possible to know by looking at the proportioning which one it is?

Thanks again for the help.

If it is CPP setup, I believe it should have some numbers on it that you can cross-reference on their website. If not, I'm not sure how you can figure it out.

[mr48chev]

the residual check valve that Hart Rod referred to is in your master cylinder. If you are still running the drum brake master cylinder there is a pretty good chance that is the problem.
The proportioning valve equalizes the braking pressure between the front and rear brakes so the rears don't grab first or too much as compared to the fronts.

You can take the residual valve out of the rear brake side of the mc, you have to take the brass seat out of the hole that the brake line fastens into ( most guys use a sheet metal screw) and then take out the little valve and spring and put the seat back in so the fitting will seal. You would probably want to get a 2lb inline residual valve then.

[fastom]

I checked the rear brakes again tonight and they are locked up again.

I'm unable to find a difference between a disk-drum master cylinder or a disk-disk on CPP's site. There is a difference between the proportioning valves however.

I'm going to assume the problem is the proportioning valve.

[chevy_mike]

Buddy of mine had the same problem on his '67 Chevelle. He never did figure out the problem with the rears, which used same Cadillac calipers. He decided to switch front and rears over to 13" Baer brakes, which use PBR style calipers and all the problems went away.

I have heard of a lot of problems with the Cadillac style calipers, you couldn't get me use them. I have used the PBR calipers on a number of vehicle and they have always worked perfect.

YMMV. Good luck.

[whatnow123]

I have rear disks and haven't had this issue at all. I do need to install an adjustable valve as the rears will lock up first, but they do completely release.

[fastom]

CPP said the proportioing valve is not the problem, not the master either! I'm at a loss. I might be going back to the drum setup.

[fastom]

Well, I found the problem! The pedal pushrod needed adjustment. I shortened the rod about .5 inch and that fixed the problem.

Thank you for all the help. Now if I could just get used to the feel of the brake pedal, hydroboost system feels different.