Rear brake pressure regulator valve, Brake repair Options

[DamonsCarrera]

The brake pedal on my 914-6 is very spongy, even after repeated bleeding with a pressure bleeder. I isolated the problem to the brake-proportioning valve or pressure regulator. I cannot seem to get the brakes properly bled with this valve in the system.

I've read other posts by some here and it seems this valve is a source of some debate . Is there some trick to bleeding the brakes with it? Do I need to bleed the brakes the old-fashioned way, have someone push on the brake pedal?

[Eric_Shea]

There is no aftermarket valve.

It is a "pressure regulator" as you've stated in your title. The aftermarket ones are bias controls, reducing fluid flow to your rear calipers. Not a good idea if you have a properly biased and designed system from the factory (1.6:1 ratio).

Here's a great read:

 Pressure_Regulator.pdf ( 83.82k ) Number of downloads: 598


Readers Digest: This spring loaded valve will slide over under pressure allowing a micro switch/check valve to shut off fluid to the rear calipers in a panic stop (525psi). Once the pressure equalizes in the system this valve brings the rears back into the circuit.

One of the first anti-lock brake devices. Meant to save a 914 from spinning (like a top) with it's mid-engine and polar moment inertia.

Did you recently rebuild the calipers? If so, the new seals are causing the pistons to pull away from the rotor at a more aggressive rate. Bed the pads and the seals will get broken in by the heat. After a while, the pedal will begin to come back up.

If not, you probably have some residual air in the system. Bed the pads and then re-bleed the rears after driving the car (bumps, rail-road tracks, etc.) All of these things help dislodge air bubbles that may be trapped in the system.

Do you have the venting clearance set on the rear calipers? If not, you'll want to set that at .004"

***IMPORTANT*** We have been finding new rear pads to be thicker than original spec. If you have new rear pads, check and make sure they are 13mm thick. Some companies have begun adding a thin metal backing plate. This will cause the need for the inner piston to be hyper extended inward pulling the pushrod away from the handbrake armature. This will cause you to have a weak or non-existent handbrake no matter how much you adjust the cable.

Solution: Remove the thin metal backing plate if there is one and/or grind the pad material down to 13mm before installing them in the calipers.