95 Lumina - starting crinkle, rev when braking?

So when I start the car, there's a strange crinkle sound behind where the pedals are like two metal pieces are clumsily moving out of the way. When I hold the brake on startup, nothing, but then the sound occurs when I take the breaks off. :sly:

It doesn't happen when I drive, when breaking after start up, or when stopping. Only the first time when I start the car.

Additionally, it idles up when I break.

I've been told it's probably a tear in the power brake booster diaphragm but I want a second opinion. Also, can one just replace just a part of the diaphragm or do I have to pay $70+ for the whole dealy? :confused:

It's not an ABS valve cycle is it? Mine does that when you start it. Weird little grunt/crunch sound from down near the brake pedal. The ABS self-tests on start.

Try this:

Start the car up, pump the brake a few times. Release the brake, shut the motor off.

Wait about 1 minute, then start pumping the pedal. If the first couple of pumps give you a normal pedal, that gets higher and firmer the more you pump, the booster is holding vacuum and the check valve is operating properly. If you hear air bleeding or the pedal is hard on the first pump, it's leaking down.

Then with it depleted, hold the brake down firmly, and start the motor. The pedal should drop immediately. If it does, everything is normal. If it drops slowly and/or you hear hissing, you're leaking.

Before going any farther, check the vacuum hose going to the booster for damage, the check valve and the grommet where it plugs into the booster.

If I turn off the car and pump it, it gets hard.

Then when I start the car with the pedal down, it releases to the floor over the period of about 1 second. Is that good?

If I turn off the car and pump it, it gets hard.

Then when I start the car with the pedal down, it releases to the floor over the period of about 1 second. Is that good?

You should get 2-3 power assisted strokes of the pedal w/motor off before the pedal starts to firm up. Do you? And did you wait a minute after shutting it off?

If the pedal softens as soon as the motor begins to run, that's what we're looking for.

The idling up when you step on the brake is indicative of a leak, however. Ever listen under the hood while someone steps on the brake? You may hear it sucking air. You can try moving the vacuum hose around and see if it starts sucking air too...it could have a split or something.

What I was trying to figure out is this...the check valve assures that stored vacuum in the booster doesn't flow backwards through the vac line...that way, if the motor were to stall or something, you still get enough assist from the stored vacuum in the booster to stop the car with assist.

So if it will store vacuum, and provides assist after shutoff and after waiting a minute, it is safe to say the problem is not in the booster or the check valve...more likely the vac line or it's connection.

If it bleeds off vacuum after sitting for a minute, the booster or check valve would be suspect.

Oh I understand now. I just rechecked it and it stored pressure 2min after I shut off the engine. In other words, the power assist worked with the engine off for at least three good pushes.

So I should check the vacuum line? Where is it? What exactly am I looking for?

Looking at the booster (big round can the master cylinder is bolted to) you'll see a vac line going into it...follow it all the way to it's source at the engine's intake manifold...

Make sure it fits tightly where rubber meets metal, no splits, no weak spots, not pinched or rubbing...make sure the hose fits tightly onto the check valve at the booster, make sure the check valve fits snug in the grommet on the booster.

I think on mine the hose coming off the booster runs into a steel line on the firewall, then another rubber line on the other end takes it to the intake manifold, if I remember. Too dark to go look right now...