Brake booster performance

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Bwana

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Is there any way to check to see if the brake booster is doing it's job? Somehow the pedal feels like it's getting harder to push for the same amount of stopping power. When I shut off the engine, it does bleed off to where the pedal is rock hard but I can feel it depress further like it should as the engine starts up and the vacuum increases.

It just doesn't feel quite right. And if it were leaking, wouldn't it play havoc on the MAP and idle speed (CSi)? Is it supposed to hold a vacuum for some time after the engine is shut off? Everything else is tight, rebuilt the master cylinder and slaves a couple of years ago and no current leaks.
 
Yes, the check valve holds just fine. However, I can't get any vacuum build up in the servo. I'm using a brake bleeder vacuum thingy (that's a highly technical engineering term :lol: ) to try to pull a vacuum on the servo but no luck. It has a vacuum gauge built on it so I can see nothing is happening. So I'm assuming either the diaphram inside or the o-ring that seals the master cylinder to the servo is bad.

The blue books talk about the brakes not performing well if there's no vacuum so I guess that's it. It still doesn't make sense that the idle isn't wonky (another technical term) because of the excess air from a possible leak. I'll try running it later this week with the vacuum tube blocked off to the inlet manifold.

Servo's are NLA from BMW. Anybody ever rebuild them? Today's job is to hunt down one that I know has a good diaphram.

Edit: What are the two relays for that are on the side of the servo bracket?
 
You could call these guys and see if they rebuild e9 servos:

http://www.boosterdeweyexchange.com/

Maybe pump a little low psi air into the vacuum hose to see if you can hear where it comes out? If it's the master cylinder gasket then that would save you the trouble of going after the wrong item.

Can't help with the relays, maybe cold start for your injectors is one of them.
 
Plenty of places to rebuild your booster- about 200 bucks.
My test for brakes is simple, if you can't lock up the wheels something is wrong. Good BMW brakes should be able to toss you into the windshield.
Don't forget the o-ring at the booster at the plastic hose fitting.
There is another vacuum test- drive car, pull over and disco hose to booster after the check valve. No whoosh means no vacuum.

I use these guys.....

http://www.pwrbrake.com
 
OK, I'm lined up with the guys sfdon suggested, price about right. So the question is, do I paint it gloss black or do I have them powdercoat it (included in price). Gloss or matt? What was original?

Also, I take it that I have to remove the whole brake pushrod from the pedal out when I remove the booster? Probably why the blue books recommend moving the power steering resivoir out of the way? Somebody must have done this before?
 
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The saga continues!

And I've forgotten my Photobucket username and password combination so I can't post pictures!

Anyway, I got the booster back from pwrbrake.com, they did an excellent job. The area around where the master cylinder mates to the booser is a little rough, even after powder coating. Is there a product to use on the square "o-ring" that resides in the cylinder? I'm considering something like silicon sealer but I've always hesatated doing that for a number of reasons.

Is there something else, specifically for O-rings that lasts and will ensure adequate sealing?
 
61porsche said:
Locktite 5452. Sealer for o-ring boss.
Click to expand...

Got it from Grainger for $55/tube Holy $hit!!!

http://www.grainger.com/product/LOC...m/rp/s/is/image/Grainger/6JZW3_AS01?$smthumb$

I sure hope it works. I'm not a piker when it comes to spending on the Coupe but wow!

Here's a picture of the wear I'm talking about. Hope this stuff handles it.
PC150529_zpsba84c68c.jpg
 
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