After several days of the brake pedal getting softer and softer, I decided the factory original Master Cylinder was failing and replaced it with rebuilt unit. The result? No change. Tried bleeding the brakes with little results.
Could the brake booster be to blame? Does anyone know how to test it?
Any help would be appreciated!
------------------ One-owner '88 Coupe 178,000 miles and counting...
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09:22 PM
PFF
System Bot
topcat Member
Posts: 5486 From: Charleston SC Registered: Dec 2001
Did you bench bleed the new M/C before installing? I do not know for sure, but the booster should cause the brakes to be harder to apply, not give a soft pedal feel.
You also have a PM
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09:48 PM
GTDude Member
Posts: 9056 From: Keysville, Virginia, USA Registered: Nov 2001
Yes, a hard pedal would result from a bad booster. If you have a soft pedal, you either have air in the system, a bad master cyl., or a misadjusted system....rear brakes and park brake. Bench bleeding of master is essential. Good luck.
Phil
------------------ 87 FIERO GT 2.8 5spd 0-60 in 6.8 seconds!
Yes, I bench bled the Master Cylinder according to the directions that came with it. After installation, we bled the brakes but didn't get a lot of bubbles. I removed the MC and 're-bled' it off the car. Haven't bled the brakes again, yet. My helper won't be her til later. Pedal still feels the same.
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02:31 PM
topcat Member
Posts: 5486 From: Charleston SC Registered: Dec 2001
Yes, I bench bled the Master Cylinder according to the directions that came with it. After installation, we bled the brakes but didn't get a lot of bubbles. I removed the MC and 're-bled' it off the car. Haven't bled the brakes again, yet. My helper won't be her til later. Pedal still feels the same.
Results? Curious minds want to know.
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06:47 PM
buddycraigg Member
Posts: 13620 From: kansas city, mo Registered: Jul 2002
you may have a leak somewhere and possibly be sucking air back in to the system. bleed each tire one at a time. when you notice a big change then you have found the circuit that could possibly be failing.
and the others are correct, when your booster fails the brakes will be harder to depress and you may even hear a vacuum leak.
Thanks guys, I'm convinced that the problem is my minimal brake bleeding experience. Brake pedal is firmer now, but under hard braking the "BRAKE" light on the dash will light. The car stops now, but not well. Should I bleed the brakes w/the car running, in order to use the power of the booster? We've done all the bleeding with the engine off.
Thanks again, LJ
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09:32 PM
buddycraigg Member
Posts: 13620 From: kansas city, mo Registered: Jul 2002
when your ready to bleed the brakes again the best way to get most of the air out of the system is to place a drain pan under all the bleeder screws and crack them all open, fill the master cylinder resavoir full, then just keep an eye on it leve it sit for a bit but keep the M/C res. full. then oncre you see fresh fluid comming out of the bleeder close it off. Do that for the remaining wheels. after that is done you should have good brakes and you shouldnt need to bleed it again. However you must first fix the air leak or else youl be wasying your time and expensive brake fluid :P Oh and if you still want to test the booster where the vacum line goes into the booster can there is a check valve (thats the little plastic part where the hose conects)try to pull that out if you hear a hiss that means your holding vacum you should be able to hear the hiss evan if your car has been shut of about 2 or 3 days. if not then you either have a leaking booster or a bad check valve.
