We had a lot of problems with the proportioning valve while bleeding. It would often shut the flow to the end we were bleeding.

 

Ok, so I checked some posts about removing the ABS... as I did before doing the job. But none of the ones I have read mention anything about installing a pressure check valve. I see that there are different rating on these, and not sure what to try. Have you had first-hand experience with this? Which one did you use?

 

A residual pressure check valve is necessary for drum brakes, because without it the fluid in the wheel cylinders would be pumped back into the master cylinder by the brake shoe return springs. If this happened, everytime you stepped on the brakes the shoes would have to move a fair amount further before contacting the brake drum, there would be some lag time and you would have a low pedal. The check valve keeps about 5-8 psi of pressure on the drum brakes, this is not enough to overcome the shoe return springs and force the shoes against the drum, but it is enough to stop the shoes from pushing the brake fluid back into the master cylinder. The check valve is normally located in the master cylinder outlet where the brake line screws in. It is only on the drum brake section and the disc brake section will not have one. You can buy adjustable ones that can be installed anywhere you want in the line going to the drum brakes.

 

Just my 2 cents, Have you checked the vacume reserve ball for a leak? I'm not sure if that's inline with the brakes, but on mine it leaked and gave me vacume problems!

Clancy, Did all 95s come with a check valve for the drum brakes, or is that an after market thing? Also how do you tell if they are bad??

 

Any vehicle with drum brakes requires a residual pressure check valve for the above reason. They are available as an aftermarket item in fixed and adjustable configurations. The nice thing is you can have more then one in your system, they don't add up as it were. In the mastercylinder, they are very small and located just behind the flared fitting at the outlet to the drum brake side. It is often just a piece of rubber held against a seat by a small spring. When they fail you get a lower than expected brake pedal, but usually the brake warning light does not come on. If you replace your mc with one from a later year vehicle that has four wheel discs, there will be no residual pressure check valve in the mc. You will have to install one in the line that goes to the rear drum brakes. Installing one in the disc brake side would cause the brakes to drag all the time.

 

Just so I'm clear, can you see the check valve from the outside of the MC, or is it on the inside of the MC? Also do they sell them as OME and what's the cost??? One more thing, will I have to bleed the brakes if I replace it?? Thanks

 

I have done some further reading in my old brake manuals, and it appears that you may not require a residual pressure check valve if your rear wheel cylinders have a spring in between the two cups. It serves the same purpose as the check valve by pushing the cups out instead of the brake fluid pressure.
To answer your question, about whether or not you can see it on the outside of the mc. No, it is internal, and if you have one it will only be in the rear brake section of the mc. However should you decide to install one in the system, many hot rod shops will sell you one that is installed inline (between the mc and the combination valve). The nice thing if you do this, it does not have a multiplying effect on the amount of pressure on the system. So if you put one in that is a six pound settng and you have already got one in the system they don't add together, but will stay at whatever was the highest setting. The cost of an aftermarket one should be adbout 20$.