View Full Version : Brake Proportioning Valve?

08-09-2009, 03:29 AM
I've had my car for a few years and most of the lights in the dash were not working. After replacing them, my brake warning light comes on.

I bleed the brakes and it seems to be ok for about a week. I have to have someone help me do this as gravity bleeding only gets fluid, and won't center the valve even after a hard stop or pedal pressure.

Not knowing if the proportioning valve was centered for the longest time, I was wondering what could be the best way to troubleshoot this.

I just had the car aligned and all the bearings were checked and no pulsation is noticed.

Do these have the springs on both sides of the piston to re-center them?

I was wondering if it had been in the failed position for a long time if it would fail to that side falsely or if the front spring is stronger... are they pron to failure,to many questions :hissyfit:

08-09-2009, 07:14 AM
Pressure centers the piston. Stomp the pedal hard a few times, that'll center it. Being a tandem master both circuits will have the same line pressure when depressed. (not going into how the center spring between the 2 pistons affects pressure tise through each indiv. circuit)

The valve is a little piston with the center milled down thinner. When it's in the center position the contact tip on the switch will not contact it. If the piston moves off center the 2 will make contact, grounding the circuit and the light turns on. If it's stuck off center the light will always be on. You have a leak somewhere.

08-09-2009, 12:41 PM
When I pull the cap off the master cylinder, there is no fluid loss.

I started this year with a new MC (bench bled) and booster, and completely bled all calipers. Each time I check fluid, none lost and no leaks at any calipers:twitch:

I will have to re-check rotor run-out and just by chance I did see a lot of talk of re-built vs new MC. I may have gotten the wrong one but not likely as both reservoirs are equal in size.

The only logical explanation would be air from pulsing at the rear rotors, but it checked out fine when I checked earlier this year.

The only test I found for the proportioning valve needs a pressure test and I don't have the gages.

08-09-2009, 06:26 PM
The MC could be leaking internally.

08-18-2009, 02:21 AM
Well, I finally got my head out ...:banghead:

As the rear failed, and the valve blocked off the low pressure side, I opened a front bleeder and the valve switched to the front. Good Valve!!!!

Now the bad news... it's the rr bearing. No noise, but with the fixed caliper, it is a virtual pump as my last trip was on a long stretch of rough bumpy roads.... Time to rebuild:crutches: