Symptoms of a bad brake booster?

[Jean]

Hard at first but then spongy?

[Highway1]

It's hard right way and then i can feel the pedal depress. Maybe this is just the way e30's are.

[Imagine_M]

When you push on the brake does it move about an inch or two then you have to push hard or is it hard right away?

If it moves then is hard your brake booster is not operating correctly!

[Highway1]

i just replaced the MC and no difference. I fucking hate my life

[Highway1]

Calipers were rebuilt last week

I was thinking maybe it was vacuum too but then i talked to someone who said it probably wasn't because it feels the same at all engine speeds. I can downshift into 6K rpm and the brakes feels the same as when I'm idling.

[jlevie]

thanks but there no air in the system for sure. and they are not sticking. i bled the brakes four times and the pedal feels SOLID with very short travel but my brakes just don't grab at all and i have to push hard to stop fast. i guess i'll just have to try a different MC

Higher than normal pedal pressure can also be the result of insufficient vacuum to the booster. That can result from intake leaks or a problem with the check valve or booster hose.

[E30Gus]

How old are the calipers? I've had the same problem for a while even with a new MC, booster. I rebuilt a whole set of calipers and put them on and what a diff it makes. Stops like a new car.

[Highway1]

thanks but there no air in the system for sure. and they are not sticking. i bled the brakes four times and the pedal feels SOLID with very short travel but my brakes just don't grab at all and i have to push hard to stop fast. i guess i'll just have to try a different MC

[e30huh]

check for air in the system and rebleed again, make sure the calipers are not sticking

[Highway1]

thanks but if you read my post above yours i have already put one in. does anyone have an idea why my brakes are so unresponsive? or should i replace everything else.

[sushipower]

Got one for sale with the input shaft already modified.

[Highway1]

ok so i put an e21 booster in today and the problem is still there. The pedal feels solid but there still is hesitation when I first step on the brakes. could it be the abs unit?

[Highway1]

thanks, I guess ill try and find an e21 booster or some sort to make things easier in the future.

[jlevie]

A hard pedal is almost always a failing or failed booster. In this case it sounds like it might be the vacuum valve in the booster. If you get a used booster, check the booster for oil or brake fluid. Either of those in the booster will cause the diaphragm to fail. If you get a new booster, use a new master cylinder.

[Highway1]

My brakes have a split second delay when first stepping on them. They don't feel spongy but when i first step on them the brake pedal wont depress right way it feels hard at first like something is clogged in the line or something.

So far I've tried,

New brakes lines
New pads/rotors
Rebuild the calipers
Different MC from junkyard
TWO different brake boosters
Different ABS pump


NONE of these has made a difference

anyone?