LoneStarS30Z

Yet another brake issue thread! Let me start off by saying I've searched and searched, and done most every solution that I've come across.

Long story short, I replaced all my brake lines, rotors, and pads.

My problem is that even though I'm getting pretty strong brake pressure, the pedal will slowly sink all the way down if I push down hard enough. Also the brake pressure is intermettent. Example, one stop, the pedal is rock hard and engages early, other stops, I'll have to go down about halfway then it's solid, next time it's back to engaging up high. Despite of what position the pedal engages, I can still manage to make the pedal sink to the bottom with enough pressure. It's a slow sink, but a consistant one at that.

List of things I've done so far:

-Old fashioned 2 man bleed
-Gravity bleed
-Wedged the brake pedal down overnight
-Double digit ABS stops, followed by bleeding.

Everytime I bleed I get constant fluid, no bubbles. I just ordered a brake master cylinder kit to preform a bench bleed per Rob Robinette's website. I have no visible fluid leaks, and the hose running from the intake manifold to the brake master cylinder looks great. Keep in mind this is a vehicle with only 58,000KM's on it.

Is there anything else I'm missing here?

macr88

I think it may be a faulty brake booster, I vaguely recall my buddy having this same issue after bleeding his brakes, it seemed like a bad master cylinder so he replaced it and the problem was still there so he did a bench bleed and still no go. He thought maybe he had a bad replacement mc but in the end it ended up being the brake booster.

I'm not all that familiar with brake boosters but was always under the assumption that anytime you have a pedal that slowly goes to the floor then it was a leaky MC but after his issue and confirming with the shop I go to it can be the brake booster as well.

Rays S2k

What year s2000

zeroptzero

^ This. If you put your foot on the pedal and push lightly and it drops towards the floor it is a bad brake booster. Otherwise I think you are having brake booster issues. It would help to know the model year as there was a recall on the Ap2 brakes.

LoneStarS30Z

Sorry fellas, this is on a 2001. I'll look into finding a replacement. Any speculation as to why the brake booster would fail?

zeroptzero

That can happen on any vehicle, just age and normal wear and tear. Shoot me a pm and I can email you the Brake Booster test per the service manual (if you don't have a service manual). You should test it to be sure so you don't throw money out the window, despite it sounding like a booster failure.

ssonsk

does the pedal get hard if you pump it?

LoneStarS30Z

With the engine off, it does build pressure and it'll hold just fine. But with the engine running the pedal gets the slow sinking motion.

Following the test procedures via the FSM, it was looking like both the booster and BMC might be bad. I'm just going to try another booster first since it's the easier component to swap and if that works I'll move onto the BMC.