The Stovebolt Site Forums The Shop Area Driveline Front discs binding after short drive

I have a 54 3600 with the CCP front disc brakes and power booster. Its been fine for three years and just last week I smelled brakes on a 10 mile drive. The front wheels were hot but the backs were fine. I jacked up the truck and couldn't spin the front tires until I cracked the bleeder screw. I pumped the pedal 2 or 3 times and the wheels locked up again. I pulled the calipers off and the pistons pushed in with a c clamp without much resistance. Could it be in the master cylinder or the residual valves? I don't want to start replacing parts I don't need to. Need help on diagnosing please.
Thanks Sharon

Why do you have residual valves on disc brakes?
Jerry

I thought they might be built into the master cylinder. UPDATE. I adjusted the rear shoes and found they do not bind at all only the fronts. There is 1/8" free play in the pushrod to the booster also.

Try loosening the flare nuts upstream of the flex lines in the front. It's unusual for both flex lines to fail at once, but not impossible. If the calipers stay applied with the metal lines vented upstream of the flex lines the flex lines have collapsed inside.

Edit: some boosters have an adjusting screw between the booster diaphragm and the master cylinder, but that one would probably affect all the brakes if it's out of adjustment.
Jerry

Thanks Jerry, I will give that a try.
Sharon

Sharon,

This explains why your front disc brakes have residual pressure valves:

https://techtalk.mpbrakes.com/how-to-series/four-things-to-know-about-brake-valves

Obviously your overall system is correct for your application or it wouldn't have worked perfectly for 3 years. Now something is keeping hydraulic pressure on your calipers when you take your foot off the brake pedal. I would use a process of elimination releasing pressure at the MC flare nut first, then at the residual pressure valve and finally at the caliper and see where in the system the blockage is.

Good Luck!

You need residual valves because the master cylinder is level with the calipers without the residual valves the brake fluid will back flow into the master cylinder . There’s one for the front and for the rear

If residual valves are used with disc brakes, they need to be VERY low pressure items. Calipers have no springs to retract the pads away from the rotors, so residual pressure in the lines above a pound or two will create drag and overheating. It also takes very little pressure to move the large diameter caliper pistons, compared to a drum brake wheel cylinder. The heavy spring pressure of drum brake shoe retracting springs allows much higher static pressure to remain in the lines, which also keeps the wheel cylinder cups expanded against the cylinder walls to avoid air leaks into the fluid.
Jerry

Thanks for the info. I will remove the flex hoses first and see if I blow thru them. then onto the calipers being the right side drags considerably more than the left.
Sharon

Pulled of the right flex hose tonite and you can blow thru it. Ordered a couple of caliper kits and will put them in in a couple of days. Keep everyone informed.
Sharon

Given the hoses are ok............My guess is the “all in one valve” ( proportioning) is the cause.


http://www.classicperform.com/PVK.html


Different issue but Valve leaked in the first 90 days.

[img]http://www.classicperform.com/Images/PVK.gif[/img]

Sharon............did you get the brakes fixed ? What was the cause ?

Still curious ...........fixed ???