C15A brakes jamming

[hrpearce]

Originally Posted by Dave Mills

Have you by chance overhauled your master cylinder? Maybe just maybe if you have you could have placed the fluid return washer in back the front, upside down, etc. The washer is usually a wave washer, If this little washer is in back the front it will allow the fluid out into the wheel cylinders and will not allow it to return to the reservoir tank, keeping the brakes engaged. When you say you have released the pressure is this from all 4 wheel cylinders or from the master cylinder? Just a thought as I have suffered the same problem with my own repairs, not a C15A but never the less have suffered the same problem.

I agree with Dave it seems that the master cylinder is not allowing the fluid to return.

[Richard Farrant]

Originally Posted by hrpearce

I agree with Dave it seems that the master cylinder is not allowing the fluid to return.

This can be proven easily by releasing a bleed nipple on a wheel and seeing if it will then turn, if it does not then it is a seized wheel cylinder.

[harrygrey382]

Originally Posted by Bruce Parker

I bet the wheel cylinders are 'stale' and not releasing allowing the shoes to retract. Pull a wheel and a cylinder to see what's up. If the bores are clean then clean up all four wheels and the master, re-bleed and away you go. If pitted and full of crap...you'll know what to do.

Typically it goes the other way after a long sit. You apply pressure at the pedal and the rotten seals or pitting causes a pressure loss.

That's what I suspected - that's why I did what I did with the shoe adjusters. I put a lot of force on them to retract the pistons and nothing changed. So either the pistons are seized solid (I guess possible) or there's a mechanical obstruction.

Originally Posted by TCLARK

Also make sure there is a bit of "play" in the brake pedal when at the top. My CMP will sometimes not let the brake lights go out because all the pressure is not released. I backed off the rod in the brake master cylinder so there was play and problem solved.

Hmm not much play, I guess there's a tiny amount but the pedal is right at the top

Originally Posted by Richard Farrant

This can be proven easily by releasing a bleed nipple on a wheel and seeing if it will then turn, if it does not then it is a seized wheel cylinder.

Yep that's what I tried first up, no change. As above I guess you're right it could be a (well 4) very very seized cylinders.

Was liking the idea of the master cylinder return washer in the wrong way round, if releasing the pressure made a difference I'd be right on it. Now I just have to go and pull a drum off... Is going to be fun with these tight shoes

[Lynn Eades]

Probably the (aluminum??) pistons went in dry, and have grown (oxidized)in their bores.

[harrygrey382]

Originally Posted by Lynn Eades

Probably the (aluminum??) pistons went in dry, and have grown (oxidized)

They went in with rubber grease, could they still have oxidised?

[rob love]

12 years on a rebuilt hydraulic system is a long time. Agree with the others who say to try and crack a bleeder screw and see if the pressure leaves, but most likely you need to take er apart and rebuild it again.

Not sure about your neck of the woods, but hydraulic components are dirt cheap these days. Wheel cylinders run around $30-35 each. A Ford master cylinder is about the same price. Unfortunately not the same deal for the chev master cylinders at this point in time.

[chris vickery]

I had a similar problem on my first 12 cab when I had just fully rebuilt the braking system.
My pedal had little free play and the brakes worked great for a little while. After a couple miles of driving the brakes would stick on and the drums were heating up.
Investigation reveal led improper adjustment of the pushrod which was not allowing the fluid to release freely back into the master cylinder. As the fluid got hotter and continued to expand the result was application of the brakes by sheer hydraulic pressure buildup.
Once the pushrod was adjusted the brakes worked perfectly.