Hey Guys, my '56 has a front disc brake conversion. CPP/ Mid-Fifty stuff. The problem is the front brakes stick on at times. The rear are drums and don't seem to be affected. If I stab the brake pedal, sometimes they'll release. Other times I just over ride with power and they'll release. Is that a problem with the purportioning valve or residual valve. There is no external inline valve. It's supposed to be built in. It's both left & right brakes, not one more than the other. How do I determine if that's the problem and how do I repair it? Open to all thoughts and suggestions, thanks, Jay

 

When you did the swap did you also replace the master with a disc / drum one?
The drum masters have residual valves just behind the flare seat that keeps a little pressure in the system to over come the drum springs so when you hit the pedal the brakes work right away.
If you did not swap the master for a disc / drum or got the lines mixed up there could be pressure on the disc side.
A disc / drum master has a large and small side to the fluid, large side is the disc side.

The other thing it could be is the master is not releasing all the way.
If you can make this happen all the time try and loosen the master and see if the disc release.
As a test you can also use a flat washer between the master and the mount to space the master out.
Just be careful doing this as it will take more pedal movement to get the brakes to stop so test first in a safe area before hitting the road.

Now you did not say if this is power or non-power brakes?
I would first check to see if the pedal has a top stop that can be adjusted to let the pedal come up more.
Power uses an adjustable rod that pushes the master plunger. If you find the above washer deal fixed the issue then make this rod a little shorter.
If non-power does the rod from pedal to master adjust? If so make it a little shorter.

I also take it the rubber hoses to the front brake system are new?
Old ones can break down on the inside but look good on the outside and this could keep fluid from returning back to the master.
I have never seen a purportioning valve keep pressure on the system just the other way, would not let fluid pass to the wheels.
But guess anything could happen?

Oh just a thought if you think it is pressure not releasing you can also undo a brake line fitting to see if the pressure is re-least that way but can get messy with the fluid and all. Undoing the master from the mount is easy and less messy.
Dave ----

 

I have a disc/drum frame mounted stock pedal setup and the brake pedal did not return all the way and the brakes drug, ended up using a return spring and that fixed it

 

Hi Thanks for the reply. This power disc brake has been on my truck for several years. working properly. This just started recently, return spring is working, and everything works fine but sometimes the front brakes stick. It happens when I brake hard. Normal braking seems OK. If I'm sitting at a stop and resting hard on the pedal, they won't release, as well. Thanks, Jay

 

That sounds like a brake maintaince thing. I would take the calipers apart, clean and relube them.

 

Sounds like caliper piston sticking in the bore, may time to replace them. When the piston sticks, you usually will see one pad worn more than the other, could also be the pins the caliper ride on are binding....clean and lube them as stated above.
w

 

Hi, thanks for the reply. I think I have narrowed it down to the metering valve. There is a reset process, but I think I'll just replace it......Jay Daggett