1999 Suburban Brakes Wooshing...

Vacuum leak?

Reply to
Mike Copeland
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My '99 'burb is making a strange sound lately when you push on the brake pedal. It sounds like air is leaking from them, although that can't be right. Is there some sort of air-actuated control on them? I checked the resevoir and it is full, when I turn the truck off, the noise stops and the pedal seems to get stiffer. The brakes seem fine at higher speeds, but at lower speeds under 20mph, they seem weaker.

Any ideas???

This is a 4x4 with power everything and the 5.7 liter Vortec.

Thanks

Reply to
MASTER Brian

I don't know, it seems to be coming from under the dash! I'll look for vacuum lines.

Reply to
MASTER Brian

Is it just a whoosh as you move the pedal, or is it a constant sound the entire time the pedal is depressed? If it is the second, the diaphragm on the power booster has a hole and the booster needs to be replaced.

Whitelightning

Reply to
Whitelightning

ABS brakes?? ABS brake relay, under dash??

Reply to
hustl3r

I think you are correct. I looked up under the dash, where the pedal goes through and when I press on the rubber boot as the pedal is pressed it sortof stops/changes the whooshing sound.

My only other question is do the brakes need to be bled after replacing?

Thanks for the help...

Reply to
MASTER Brian

On some cars you can leave all the brake lines hooked to the master cyl and just move it out of the way when replacing the booster. If so in your case there is no bleeding involved at all(try it for sure). If you need to remove the lines then you usually just need to bleed the master when done. Either way not a big deal. I'm not so sure you have a problem....this is important.-Does the noise only happen when the pedal is moving? If so I would re-think replacing the booster.

Reply to
ShoeSalesman

Yes, the sound only happened, when I pushed the pedal. At least as far as I could tell. If I pushed in on the rubber boot then the noise would somewhat go away. I went ahead and replaced the booster and all seems good now. I didn't bleed the brakes, because none of the lines were opened up.

What else would have you looked at?

Thanks for the help!!

Reply to
MASTER Brian

a little silicon spray at that rubber boot will fix a lot of weird noises.

Reply to
ShoeSalesman

Reply to
MASTER Brian

Still confusion on the issue Trying to get crystal clear the question is does it make the noise ONLY AS the brake pedal is being depressed, or does it make the noise the ENTIRE TIME brake pedal is being held with STEADY pressure?

Noise as the pedal is depressed is ok, its sucking air in as the diaphragm moves forward, usually there is a "felt" like material around where the shaft enters the booster that filters the air, and also muffles the noise. Noise when the pedal is being held steady on is not normal, and is usually the sign of a diaphragm with a hole in it. Also results in hard pedal, and little or no assist if bad enough. Low assist can also be caused by a vacuum leak under the hood some where. Went round and round with a Monte Carlo belonging to the alignment tech where I worked one time till we found he had a manifold leak to the oil galley area.

Whitelightning

Reply to
Whitelightning

Sorry, maybe I wasn't clear...the noise was the ENTIRE TIME the brake pedal was being pressed, except if I pushed as hard as I could and held it. In which case, I could feel resistance to my foot building back up. The other symptoms were similar to what white.lightning posted as well. I had my wife press and hold the brake pedal and I pushed the boot towards the booster and it seemed to make the noise less, but still didn't stop it.

Reply to
MASTER Brian

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