Brake Problem

[bossrod]

I've got disc brakes in front and drum brakes on the rear of my 72' C-10. The rear brakes keep freezing in the braking position. I have a new master cylinder, an old booster and proportioning valve. The linkage from the cab to the booster appears to return to normal after the brake pedal is released but the rear brakes continue to ingage. Any ideas what might be causing this?

[Orange]

Sounds to me like your prop. valve is holding pressure on them after you let off the brakes. The prop. valve for disc/drum acts like the residual pressure valve as well for your rears, so it could just be keeping the fluid held after you release.

Mike can fix you up with one for cheap if that's the problem. (He's a board vendor).
www.bumpandgrindgarage.com

Might want to listen to another person though before going with just my advice.

DLB

[cdowns]

you did bleed the brakes when the master was replkaced right?/well first i'd try cracking open one of the bleeders on the rear brakes to see if there is a pressure buildup //if not i'd pull the drums to see if theres excess build up of crapcrud on the backing plates preventing the shoes from retracting or if theres weak broken or damaged return springs

[bossrod]

I'll check that out first as the proportioning valve is not new.
Thanks

Originally Posted by Orange

Sounds to me like your prop. valve is holding pressure on them after you let off the brakes. The prop. valve for disc/drum acts like the residual pressure valve as well for your rears, so it could just be keeping the fluid held after you release.

Mike can fix you up with one for cheap if that's the problem. (He's a board vendor).
www.bumpandgrindgarage.com

Might want to listen to another person though before going with just my advice.

DLB

[bossrod]

I bled the brakes and followed the steps to bleed the master. I'll check the rears but all the hardware is new. Could be the proportioning valve as mentioned above but I don't want to leave any stones unotuched.
Thanks

Originally Posted by cdowns

you did bleed the brakes when the master was replkaced right?/well first i'd try cracking open one of the bleeders on the rear brakes to see if there is a pressure buildup //if not i'd pull the drums to see if theres excess build up of crapcrud on the backing plates preventing the shoes from retracting or if theres weak broken or damaged return springs

[quickpm]

If you do decide to get a proportioning valve, I did buy an aluminum nonadjustable one from Mike's Bump and Grind a few months ago and it worked great. It came with the bracket to mount up and new short lines to the master cylinder. I'm happy. All the other brake parts (master brake cylinder, rotors, calipers, pads, drum covers, spring kit, and shoes, everything new except lines) came from Oreilly. I could probably stand to replace the rubber parts, too. Check the rubber brake line on the rear axle, it could be deteriorating.

My truck stops really nicely now- but after I put all the new parts in I still had to blow compressed air through the lines, then rebleed, to get it to work right. My problem was that the rear brakes didn't seem to work at all even though everything was brand new. You might want to try that, too. Sorry for the rambling post.

[bossrod]

I'll keep that in mind if the proportioning valve is bad.
Thanks

Originally Posted by quickpm

If you do decide to get a proportioning valve, I did buy an aluminum nonadjustable one from Mike's Bump and Grind a few months ago and it worked great. It came with the bracket to mount up and new short lines to the master cylinder. I'm happy. All the other brake parts (master brake cylinder, rotors, calipers, pads, drum covers, spring kit, and shoes, everything new except lines) came from Oreilly. I could probably stand to replace the rubber parts, too. Check the rubber brake line on the rear axle, it could be deteriorating.

My truck stops really nicely now- but after I put all the new parts in I still had to blow compressed air through the lines, then rebleed, to get it to work right. My problem was that the rear brakes didn't seem to work at all even though everything was brand new. You might want to try that, too. Sorry for the rambling post.

[68gmsee]

bossrod,

New recruit here. I was reading the different posts and happened to see yours with the brake problems. Did you find out what caused it?

I had the same thing happen to my 69 some years back and after spending a whole weekend checking everything I could think of, I found out that the rubber brake line on top of the differential where it goes to the frame was the culprit. It had swelled up internally that it was allowing "pressurized" fluid to the brake drums but was not allowing it to go back causing the rear drums to lock up.