my brake booster looks bad; by the way whats inside?

[76bimmer]

Dear FAQ,

I own a 1976 2002.

As far as I can tell, the big tin round thing that my master cylinder attaches to is called the brake booster servo.

I looked up at the bottom of my cars booster from under the car today. It was rusty and it looked like it was leaking brake fluid.

Can anyone give me a quick explanation of what the brake booster does and what is actually inside there? Does it have brake fluid in it? Can it be repaired?

Sorry to be so ignorant on this subject but I never had to work on one of these. And my cheapo Hayes manual doesn’t say much about it.

Thanks.

[KFunk]

Its just an empty can, which is literally a vacuum. It uses vacuum pressure to give you the 'power-assist' to make it easier to push the brake pedal down, and multiplies your force. It shouldn't have fluid in it.

The fluid is likely coming from your master cylinder, and leaking back into the brake booster. You're gonna need to change that master cylinder.

[Timmer]

The main component of the brake booster is a large diaphragm, along with a couple springs. Kevin's reply makes the most sense, that is, the master cylinder most likely needs replacement due to the brake fluid leaking into the booster. I've only had one brake booster gone bad out of the 8 2002's and 3 NK bimmers I've had, the diaphragm had gone in my '69 2000 a couple of years ago; symptoms were a hissing noise when applying the brakes,surging idle, and the car would really shudder when the brake pedal was depressed.

Tim

'69 2000

[c.d.iesel]

REPLACE THE MASTER CYLINDER and

mop out the booster - removing all brake fluid best as you can

before installing the new master culinder - the fluid will attack the seal inside - if the booster goes 'bad' = you will develope

a very hard brake pedal and poor stopping power. Pray.There is no servicing the booster - it's a sealed unit and not to be opened.

[winstontj]

There is no servicing the booster - it's a sealed unit and not to be opened.

HAHA.... It CAN be opened... only not re-used once opened!

[Guest Anonymous]

I have a spare one with MC if you need it. Call me (972)8415956

J.E.2002

[colorobo2002]

Here's a good website if anyone wants to check out how most anything works.

http://auto.howstuffworks.com/brake.htm

[76bimmer]

winstontj,

fantastic shot. i couldn't have asked for a better answer. thanks again.

76bimmer

[winstontj]

winstontj,

fantastic shot. i couldn't have asked for a better answer. thanks again.

76bimmer

No problem! If you look on the left half you'll see a little.... took the time to play with paint...

Check out inbetween the red lines. That's the rubber diaprham. Thats' what goes. If you look you can see my left hand is holding where the pedal lever will push. This drives that pin (in the middle) into the MC. You can also see the vacuum hose hole. It sucks on the flat plate flush against the left part. The bead between the red lines is the actual rubber diaphram that keeps a vacuum on the one side and allows foot pressure to be assisted. You can see the surface rust in this unit and it was a good one. I can't imagine what a bad booster would look like inside - probably all rusted out and crappy...