so my brakes make a woosh sound when I press the pedal. the pedal only gets hard on the floor and barley stops the car. I have grand am swap on the rear, flushed brake fluid, bleed all the calipers, bleed the master cylinder too, but to no avail. So I'm pretty sure I need a new master cylinder but what do you think before i go buy one?

quote Originally posted by IanT720: so my brakes make a woosh sound when I press the pedal. the pedal only gets hard on the floor and barley stops the car. I have grand am swap on the rear, flushed brake fluid, bleed all the calipers, bleed the master cylinder too, but to no avail. So I'm pretty sure I need a new master cylinder but what do you think before i go buy one?

I'm not really sure what you mean by a "whoosh" sound. Do the brakes feel like they're scraping? Were the brakes doing this for a while, or did it just start doing this all of a sudden? Was the car sitting, and now it's doing it?

Do the engine RPMs shoot up when you apply the brakes? If they do, that's indicitive (usually) of a failed brake booster. It means the diaphram inside is leaking. You would also know the booster is bad because it would be really hard to stop the car since you would be getting no brake assist at all. All the effort would be on your right foot.

Do the brakes feel spongy? If they're spongy, then that is more than likely the brake master cyl. Did you recently change it or something?


Let us know the status of the car (has it been sitting, did it just start doing this out of the blue, etc...) and I might be able to give some more help.

Noise from booster... ignore it.

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Yes it has been sitting for awile from the previous owner. The pedal is spongy very soft. It has new pads. When you push down the pedal you hear this whoosh sound like air I guess but I bleed everything multiple times so I figure it's probably a bad seal on the MC.

You still have air in the system. Fiero brakes are more difficult to bleed than most cars. Make sure you have a helper and be systematic about all 4 wheels.

The woosh is a normal caused by the vacuum assist.

A good way to check the brakes for proper pedal is to with the car off pump the pedal till the vacuum is all bled off. At that point the pedal should be high and firm. If the pedal feels soft then you still have air in the system. If the pedal feels firm but low check for the rear brakes to be properly adjusted. The front totally self adjust after a few pumps. If pumping the pedal results in the pedal stopping at a higher place you either still have air or you need to adjust the rear. With the car running and the vacuum assist working the brakes will feel softer and lower so make sure you don't stop until the pedal is high and firm.

when I pump the brakes with the car off I can get the pedal firm(ish) like it will firm up but if i hold constant pressure it will start to sink lower again

A loud whooshing noise usually means there's air in the lines. Did the master cylinder run low on fluid when you were bleeding the calipers? If the master cyl runs dry while you're bleeding the system, you need to bench bleed it. Also, did you install the calipers so the bleeder screws were facing up? If the bleeder screws are facing down, you won't be able to bleed the calipers properly.

Here's a way to test the master cylinder: with the engine off, press the brake pedal (but don't press it really hard). Now, keep constant pressure on the brake pedal. If the pedal slowly sinks to the floor, your master cylinder is faulty. Either that, or you have a fluid leak somewhere.

Even after you get the brakes bled properly, the Grand Am calipers and Fiero master cylinder will still cause some slop in the brake pedal. The pedal will travel about an inch with no resistance, before the brakes start to grab. This can be solved with a master cylinder from a '94 Blazer (full-size Blazer, not the S10 Blazer). However, the Blazer master cylinder will make it harder to press the brake pedal. If that becomes an issue, you can fix it with a bigger power booster, from a '96 Chevy S10 2WD.

Best of luck!

the fluid never ran low, the screws are facing up but yes the pedal does sink when applying constant pressure.

In that case, the master cyl is probably faulty.

Just out of curiosity, are you going to convert the front brakes to Grand Am hardware too? If so, you may want to consider the Blazer master cylinder.

Okay thanks, I was but not anytime soon well would it be cheaper than a fiero MC? And would it work with the stock powerbooster for now?

A slowly sinking pedal means either you are leaking fluid somewhere (it should be obvious) OR your Master Cylinder piston umbrella seal is not sealing. Many times those seals will fail when you are pressing the pedal lightly, but seal when you apply a hard pressure. If it is doing that you need to either rebuild it or replace it.

quote Originally posted by IanT720: Okay thanks, I was but not anytime soon well would it be cheaper than a fiero MC? And would it work with the stock powerbooster for now?

The price is about the same. But with the Blazer MC and hybrid Fiero / Grand Am brakes, you're going to have to stomp on the pedal to stop the car. It would be safer to wait until you finish the Grand Am brake conversion before installing a Blazer master cylinder.

Gotcha I'm making a trip to autozome soon, I'm becoming a very frequent customer there lol.

yep the new master cylinder did the trick thanks