Bad brake booster?

[884door]

Hey guys, looking for some advice here.

Car is a 1988 325e


My brakes are usually a little mushy but occasionally they will go almost to the floor without doing much, one pump of the brakes will bring the pressure back up and braking will be normal (well...mushy) again. If i press the brakes without the engine running, or with it running and the booster vacuum hose plugged the brakes a very firm (obviously, since there is no vacuum assist). I have tried bleeding them a couple of times and bled new fluid all the way through the lines, i'm certain there is no air in the lines. The pads/rotors and calipers are in good shape. There are no leaks and I'm not losing any fluid.


When I press the brakes with the engine running I can hear air rushing out from near the pedal, I presume this is a leak in the booster where the pedal rod enters it?

The air noise, and firm pedal when vacuum is disabled indicated to me it's a problem with the booster, but the soft pedal makes me think it's the master cylinder. Everything I've read online says the pedal is usually hard to press if the booster is failing (which makes perfect sense to me)


So what do you guys think, bad booster? MC? Both? Something else?

Thanks in advance

Edit: Oh yeah one other thing, I've read about a check valve on the booster vacuum line, this is MIA on my car and there is just a metal tube connecting the 2 pieces of rubber line with little clamps securing the rubber tubes to the metal one. Might this have anything to do with it? I'm going to go get one of these for starters.

[g22]

I'd put in the check valve and go from there. The booster should be making a whoosing from inside. To check the booster block off the vacuum line that goes in the side and then tape off the hole in the booster. The pedal should be crazy rock hard but the brakes should work. If they work and double pumping doesn't change anything it's the booster. If the double pumping changes things then it's likely a master. Boosters rarely go bad but I had one do so... You could possibly have a bad MC and Booster, go troubleshoot so hopefully if its one or the other you don't waste money on a part you don't need.

[jlevie]

If the brakes feel mushy and the pedal sinks, you either have a leak in the brake system or a bad master cylinder. A bad brake booster will result in a hard pedal that doesn't sink.

[Vince30]

My master went and when it did my peddle would go to the floor when i pushed it to hard, then i could pump it back up and it would come back. When it went to the floor (and it would make that leaking noise) I would feel a hard spot right on the floor where it breaks again. There should be a vacume hose off your booster, run the car then try to pull that, if it has preasure your booster is fine. I would say master. Also look for break fluid run were the master meets the booster. Good luck.

[884door]

Thanks guys, I guess I'm going to have to get a new master, or does anyone sell a MC rebuild kit for our cars? (I haven't really searched yet but i will)