Hier mal ein paar Infos aus dem E31 Forum in USA, wo das auch sehr viel diskutiert wird:
Prepare for the job, this repair will drop lots of fluid (brake fluid, Pentosin, and a bit of coolant) to the ground between the firewall and the left front tire. Put a large baking pan under the car at that point to catch the drippings. There are two parts to the job, one inside the car and one under the hood. Spend the first 45 minutes inside disconnecting things and getting your bearings, you will be clean and less likely to get grease on the carpet. Finally, at the end of the job you will need to bleed the brakes so make sure you have a helper and the room to bleed the brakes. Also, keep in mind that these specifications are for my 1992 850i 6-speed. The fittings are slightly different for other models, particularly the 840, which I believe has an additional fitting on the bottom of the booster unit. I think Ed covered that in an earlier post.
Tools/Parts:
I use mostly 1/4" drive tools at this point in my life because they are lighter and easier to use. Specialty tools: 7mm (for bleeding the brakes), 11mm, 14mm and 17mm flare wrenches. 17mm SnapOn 3/8" crowfoot flare wrench (part number FRHM17). 13mm, 1/4" drive, flexible joint socket (Sears part number 00943199000).
1 liter of Pentosin 7.1 or 11S (synthetic); whatever the reservoir cap indicates
1 can of brake fluid
Coolant (not much is lost).
NAPA O-ring part numberBK 7272222 [
http://www.napaonline.com/cgi-bin/nc...&prmenbr=5806] or #222 at [
http://www.oringswest.com/]
I also replaced the two grommets that seal the brake fluid reservoir to the master cylinder.
Procedure:
1) Set the wipers to vertical
2) Ignition off, pump brakes 15-20 times till hard to discharge system pressure.
3) Remove interior driver's side footwell trim, including 2 plastic screws near pedals (rotate 90 degrees); 2 plastic screws on under side of leather trim; 2 plastic screws on left foot rest; open hood and remove single screw in center of hood release lever on the left foot rest. Remove lever, foot rest, leather trim (careful, there is Velcro along the console, and three retaining pins along the top), and pedal cover. Your remote entry module may be attached to the top of the cover, if so, disconnect the electrical connector and set these parts aside. There is also a black air duct that is in the way. It is held in place with a single screw. Remove it and look at the brake pedal assembly.
4) Under hood: remove four screws the hold the cabin intake cowling cover in place, then the two screws that hold the cowling in place and remove the cowling. Next remove the plastic cover to the heater valve solenoids, the two electrical connectors to: a) the solenoids, and b) the auxiliary pump. The latter is on a flimsy plastic holder mounted to the firewall with a Phillips screw. Careful, don't break or lose this. There are two brake regulator pressure switches with two contacts each. Remove the contacts and note where they go. Remove the three 'Acorn' nuts that hold the solenoid assembly in place. Gently lift this assembly and note that there are three hoses to the car, two on the front and one to the center fitting of the pump. Remove the clamps to these three hoses and using three fine wine corks reclamp the hoses. Not much coolant will be lost. Remove and set aside the solenoid assembly. Next, disconnect the brake fluid reservoir cover and using a turkey baster, remove all of the brake fluid. Remove the reservoir by gently rocking it back and forth (I had to pull pretty hard on mine). US spec 6-speeds have an extra blue hose off the back of the reservoir to supply hydraulic fluid to the clutch master cylinder. NEVER drip brake fluid on paint, it removes it. If you drip some on a painted surface, thoroughly wash down the spot immediately (I keep a wet rag handy because its hard not to drip). Now, step back and look at what is left, inside and outside the car. Rest for a bit. Outside there is the master cylinder and booster assembly about 18 inches long in total. Inside (using a good flashlight), you will see three 13mm nuts that hold the booster to the firewall and perhaps the fourth one on the upper left. That one is the most difficult to get at. This is where the 13mm flex wrench comes in. Also figure out the clip that holds the clevis pin in place on the brake pedal.
5) Take a look at what you need to do outside: there are two brake lines mounted to the side of the brake master cylinder (11mm) and one high pressure and one low pressure Pentosin lines mounted to the top of the brake booster (17mm). All of these need to be removed in order to get the assembly free. For me the most difficult one was the high pressure 17mm flare fitting on the booster. That is where I had to use the SnapOn crowfoot flare wrench with an 8" extension. Remove the 4 nuts inside and the fittings in the engine compartment and you can remove the assembly. There is also a plastic cable holder on the side of the master cylinder. Disconnect anything else that gets in the way. I used some hanger wires as retractors to pull hoses and cables out of the way.
Repair:
Keep everything very clean using clean towels and rags, this is your brake system. On work bench remove the two bolts that hold the master cylinder to the booster. Mine were held in place with LocTite so I had to use a flare wrench to remove them. There is a small ratcheting screw on the bottom front of the booster. With a rag to catch the oil and spring, remove this screw carefully. The spring has a lot of tension so be careful when you release the small screw. Keep track of the orientation of the inside parts. The offending O-ring is held in place by a big washer, so simply replace it with the one from NAPA, clean everything and reassemble. Putting the spring and cap assembly back in the booster is a bit tricky but the little retaining screw can be partly threaded in. Make sure that screw goes into the slot in the plastic cap and that the pushrod seats properly.
This is a perfect time to replace the spark plugs on bank 7-12. I did because it is the "only way to get to plugs 11 & 12." Take my advice and do this now, you will never regret it. 12 plugs at $1.80 each.
Bleed the brakes after assembly and also the Pentosin system using the Pentosin bleeder valve on the bracket with the pressure regulator (850s only). Do this one with the 11mm and 14mm flare wrenches and the engine running. Very easy.
Good luck, Jon
http://www.napaonline.com/MasterPage...ng+-+Universal
http://www.oringswest.com/
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When the brake bomb starts to fail, you will note a dramatic decrease in brake response when first applying the brakes. It is sometime dangerous as in a panick stop nothing seems to happen at first. This is because the stored pressure in the bomb is no longer there so you have to wait until the hydralic system catches up with the increased demand for action. You might also get an occasional brake warning light when stabvbing the peddle hard and the light will stay longer and longer as the bomb continues to fail.
Another test for incipient bomb failure is to remove the top of the pentosin resovoir and watch the oil rise with each pump of the brakes. If it only take 10-15 pumps before the oil (pentosin) stops rising, then the bomb is getting bad. It has lost a lot of the precharge of nitrogen and the storage isn't there.
The booster "O" ring failure symtom is oil leakage and that usually is at the area between the booster and the master cylinder. You probably will not notice any change in brake performance just a lot of oil on the floor. You might also notice that you will have to add pentosin fluid more often to replace that which is lost.
Once again, if you open the fluid resovoir, pump the brake peddle until it get REALLY hard (should be in excess of 20 full pumps) the oil should come up to 10mm below the top. Make sure that as you pump there is no further rise in oil level before you top it off, if you don't follow this procedure, as the bomb releases fluid over time, it will overflow the resorvoir.
HTH
Ed
Mwrench
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Just did a rebuild, not that difficult.... (14 views)
Message: ...actually, it is just an O-ring replacement. The part is from NAPA (part number has been listed incomplete on these boards) the number is #72-72222 BELKNAP O-ring. The NAPA part is actually a little thicker and requires a bit more pressure to re-install, but overall, not a difficult job. The O-ring is less than a dollar (usually the cheapest part causes the most headache).
When you take the old o-ring out, you will see that it no longer has a round section to it, but looks more "square".
This should cure your PENTOSIN drip 99.9% of the time. There is plenty in the E32 and the E31 archives (I think you might find more in the E31).
The biggest problem was getting an adult hand into super small spaces. I was doing a major valve train rebuild, so I opted to do the O-ring replacement from the front of the car without removing the booster.
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