Thread: sinking brake pedal

anyone have any ideas

By "sinking to the floor" do you lose all braking? If after it does this can you restore pedal by pumping?If so does it then remain hard? Or as soon as you remove pressure it recommences its U-Boot impression? Do you have braking at all? without engine assistance?

Cheers Scott

without the engine running pedal is great the problem only occurs with power assistance if you pump it it still does the same thing

Do you have braking when you have good pedal? without engine assist it will be harder but does it stop u? Have you had some1 observe the fluid behavior in the reservoir when you pump the pedal? with and without the engine running? If you have fluid movement of any sort in the reservoir you have faulty valving in the cylinder. A faulty booster is just nothing at all in the way of assit. I can think of no real reason why it is doing that.
Cheers Scott

If you pump the peddle does it stiffen up then go soft again if you hold it down.

I recently had a similar issues and it was a case of the fluid getting past the valve in the master cyclinder

yep that appears to be the issue tried a different booster on it today no difference so it must be bypassing inside the master cyl when vacuum assisted

If not the master cylinder?
The ABS modulator faulty bleeding internaly.
ABS modulator pump running.
Does the brake pedal drop only with engine running or ignition on?
ABS ecu faulty unplug modulator wiring harness at modulator.
Vac pump or manifold vac?

Regards

I had this and found two causes - master cylinder was faulty internally and a leaking bleed nipple on my front right caliper. Replaced both and brakes are perfect now.