Brakes: Randomly Sticking, proportioning valve?

[snicker]

I have done a lot of work on my brake system (drums on a 69 Charger) but I still have one remaining problem to debug. After driving around for a while the brakes will randomly stick. Normally when I put the car in drive or reverse I can let of the brake and the car will slowly start going forward or back. Randomly though the brakes will stay stuck activated. It's as if the brake pedal isn't releasing. I can drive forward a little with some force and it seems to work it out and the brake releases but it is pretty inconsistant. I don't know if it is something wrong close to the pedal or something back near the rear brakes.

The brakes on the front and back have all been completely redone including new drums, backing plates all the components, etc. The proportioning valve in the rear has not been changed and I suspect it could have some junk in it causing it to get plugged up. Could that possible cause my brakes slow to release?

If anyone could throw out some ideas to try and chase down I would appreciate it.

[Johnny SixPack]

I had the same problem with the fronts on my "70 Charger.

Talked to a buddy who knew of a way to use backpressure to open my sticking proportioning valve, but I don't know the process.

Just be careful driving your ride until you get it squared away, as I was told that the fronts (or rears depending on how the valve is sticking) could stick and then ruin my freshly installed calipers (well the pads at least) and consequently my rotors.

Already had that happen once.  

The other option is to take the valve off and completely clean it.

Same guy stated that's often the best route, but haven't seen the results yet.

The lines were fused on mine, and I didn't trust the shop it was at to do it, so it'll have to wait till my friend finishes up the work.

[snicker]

How big of a c hore is it to change the proportioning valve? Should I just get a shop to do it?

[John_Kunkel]

A drum brake car doesn't have a proportioning valve, the only device between the master cylinder and the brakes is the safety tee and it's not likely to cause the brakes to not release.

With the lid off the MC, slowly depress the brake pedal and look for a burble of fluid in the rear reservoir. If the fluid surface doesn't show movement when the pedal is depressed, the return port is blocked and that will trap fluid pressure in the system. If the car has power brakes the pushrod adjustment might be preventing full return of the piston in the MC.

[snicker]

A drum brake car doesn't have a proportioning valve, the only device between the master cylinder and the brakes is the safety tee and it's not likely to cause the brakes to not release.

With the lid off the MC, slowly depress the brake pedal and look for a burble of fluid in the rear reservoir. If the fluid surface doesn't show movement when the pedal is depressed, the return port is blocked and that will trap fluid pressure in the system. If the car has power brakes the pushrod adjustment might be preventing full return of the piston in the MC.

Interesting, I didn't know there wouldn't be a proportioning valve. I did already adjust the pushrod some in thinking that was the problem. I will focuse more on that.

[Chryco Psycho]

What condition is th emaster cylinder in ?

[Nacho-RT74]

the porportioning valve is a part of the distribution brake fluid block on disc brakes cars... what you have is just the distribuition block

[snicker]

What condition is th emaster cylinder in ?

It's not brand new but I'm not seeing any obvious problems.

[Chryco Psycho]

it can get stuck in the master too , next time it sticks try loosening the line at the master to see if it relieves the problem

[zstalker]

do you have power brakes?  if so, the booster air valve may not be closing all the way and making the brakes stay applied.
~Erik~

[snicker]

do you have power brakes?   if so, the booster air valve may not be closing all the way and making the brakes stay applied.
~Erik~

Yes on the power brakes. Interesting point on the booster air valve. I did replace the booster a while back. That may be something to look at. I'm thinking about just picking up a new master cylinder anyway since it is older.

[Chryco Psycho]

make sure the pushrod out of the booster is adjusted correctly & not deporessing the piston at rest

[itsbacon]

make sure the soft line to the rear brakes is not collapsing. i just had this problem on my newport. my big foot could force the brake fluid through the hose but the springs on the rear brakes could not force it back so the rear brakes stuck.

[Chryco Psycho]

seen that too , tough to diagnoise !!

[snicker]

The problem appears to be solved after some light testing. I replaced the master cylinder and I haven't been able to reproduce the problem after driving around and running several errands. I'll hit it a little harder in the next few days just to make sure it doesn't resurface. Wahoo!

[Chryco Psycho]