Brake help!

[aziznowarinty]

69 c10, i bought it last week. The truck has been converted to front discs. The front calipers are locked up and have been since i bought it. I changed the master cylinder i bought one for a 71 . And after much doing i got all the wheels to bleed. It took standing on the pedal to make them bleed. Bleeding freed the calipers. But you push the pedal once and the calipers lock back up. Could the combination valve be sticking? A don't suspect brake hose because both sides lock up. Any ideas? How hard is it to reset a combination valve? How is it done? Any help is greatly appreciated. I would like to drive the thing soon.

[Alex Hayley]

It is possible you have a master cylinder for 4-wheel drum brakes. Take a look at this thread: http://67-72chevytrucks.com/vboard/s...ad.php?t=34172

[71tahoe]

Could also have old hoses swelled closed.

[aziznowarinty]

I thought of that but the reservoirs are different sizes. Did the 4 wheel drum mc come with different size reservoirs?

[cdowns]

if you have the distribution valve from the drum setup it would cause the lockup due to thier residual valves

[michael bustamante]

correct, you have to change the prop valve to a disk/drum type when converting to disk brakes

[68gmsee]

As 71tahoe said... Check for swelled rubber brake lines.

Happened to me but on the rear brakes. The front were swelled but not as much. They swell on the inside allowing fluidpressurized fluid to the brakes but restricing the return flow. And, you can't detect by looking at them.

A way to check is to loosen the bleed valve and see if they will retract by prying with a pry bar or similar.

[truckdude239]

change your brake hoses and check the pro valve more then l;ike the hoses a re collapsed inside not allowing the fuild to return

[67chevy1series]

did ESLL die cauce i keep seeing that and i just wonder and if so RIP ESLL

[crushermechanic]

welcome from the boro! the hoses should fix it. good luck.

[Alex Hayley]

Did you solve this problem?

[aziznowarinty]

Not yet. I replaced the prop valve with no success. I had to order the break hoses. I just got them in yesterday. Haven't got them on yet but we'll see. The only thing left after this is new calipers.

[joes50pu]

Before you invest in new calipers why don't you try adjusting the brake pedal rod that goes into the mastercylinder. Remove the master cylinder from the booster and make sure the rod isn't set too long. If it's adjusted too long then the return port in the master cylinder will be covered and the fluid can't return into the reservoir when the pedal is released and cause the calipers to remain locked.

[72lb4x4]

When they're locked up, crack a bleeder screw loose to see if you have pressure. If you do its not the calipers.

It also seems unlikely that both calipers would have the same thing wrong inside at the same time.

Its best to troubleshoot before throwing money at a problem...

[aziznowarinty]

I'm not throwing money at a problem. My plan is to replace the entire system. I look at the 40 year plus system as completely suspect. I don't know the truck's history. It may have cost me a few extra dollars but I'm also not trusting my life to as many 40 year old parts.well worth the money.

[71tahoe]

I just noticed in 2 different posts you also called the prop valve a distribution valve. Are you sure you have the 71-up proportioning valve? The wrong valve will do exactly what you describe.