Residual pressure check valve question

[dwhip361]

Awhile back I converted my 72 duster 4 wheel drum brakes to front disc. I used a master cylinder from a 73 disc brake car and put in an adjustable proportioning valve for the rear. I don't have the original proportioning valve. The problem is that the rear wheel cylinders are new and have leaked from day one. I read that the master cylinder is supposed to have the Residual pressure check valve built in. Is this true and could the lack of one cause the cylinders to leak? Thanks for any help.

 

[Sedanman]

Did you get the wheel cylinders from Autozone? I had the same issue and replaced them with Napa parts and no issue so far

 

[ir3333]

the rear reservoir should have a residual valve but i always install a 10 lb residual valve in the rear line for insurance.If the wheel cylinders are remanufactured maybe they were honed too much over size..'just a thought.

 

[dwhip361]

Did you get the wheel cylinders from Autozone? I had the same issue and replaced them with Napa parts and no issue so far

I got them from RockAuto. They are supposed to be new not reman. I guess I'll try adding a valve to the rear. If that doesn't work I'll try new cylinders. Thanks for the help guys.

 

[69_340_GTS]

The valve, or lack of the valve, will not cause the wheel cylinders to leak.

 

[ir3333]

The valve, or lack of the valve, will not cause the wheel cylinders to leak.

..wasn't the idea to add a small amount of pressure expand the cups slightly to hold tight
to the bores as well as take up play...

 

[dwhip361]

..wasn't the idea to add a small amount of pressure expand the cups slightly to hold tight
to the bores as well as take up play...

That's what I was thinking

 

[nm9stheham]

The residual pressure is to just keep the springs in the drum shoe system from pulling the shoes back excessively from the drums. It has nothing to do with expanding the seals behind the cups. BTW, a 10lb residual valve is high and is normally used in certain race applications. 2 lbs is more normal for street use.

However, the OP already has a residual pressure valve. The 73 master cylinder will have a low pressure residual valve built into the front port (the port that feeds the rear brakes).

As said, the rears leaking is just faulty rear wheel cylinders. Replace them; don't waste your time and money on adding a 2nd and completely unnecessary residual valve.

 

[ir3333]

O.K....good info!