Residual Pressure Valves

[GreggDaniels]

I have 4 wheel drum brakes in my car. I have read many times that with the mc below the wheel cylinder the seals in the wc have a tendency to relax enough to allow air into the system. Apparently they need a certain amount of pressure to maintain their seal. 10 lbs is enough to do that without overcoming the spring pressure that pulls the shoes away from the drums. I really don't know for sure if I need them or not but as said on this thread they are cheap insurance. There are others here that could better tell you if you might need them on the back with your drums but it is a little food for thought.

 

[Wild Mango]

I just found out firsthand that I can't use residual pressure valves in mine. I installed them bled my brakes,and my front wheels will not turn so that answers that question, at least for my car. Two steps forward and one back but I"m gettin there.

All residual pressure valves are there to do is to keep the seals firmly set on the cylinder walls. Is all. The different pressures, 10lb for drums, 2lb for discs is because the drum shoes have return springs, the disc calipers don't. If you bled the brakes and the fronts don't turn, assuming you have the correct rated RPV's, I would check that the piston in the MC is returning all the way back. If it is I would then look for sticky pistons. For a quick test, crack the bleeder on a locked wheel, if theres pressure there you'll know it, and the wheel will then turn.