Brake Booster (Servo) Leak - E34 540

[black_bird_blue]

O Learned Denizens,

I've finally pinned down the mystery steering fluid leak in my 540. It has been seeping out the back of the brake booster and into the passenger footwell.

I think what has happened is that I've been using the wrong fluid and the high level of fluid of circulation in the booster has given the wrong fluid the opportunity to attack the seals. I've recently replaced the steering box with a genuinely "remanufactured" one from ZF (as against the "reconditioning" I had done on the old one, which was worth naught. This was the point I realised I'd been using the wrong fluid (ie not CHF11) and so I'm expecting fall-out now the whole system has been flushed and bled. Next stop the self-levelling rear suspension, I'm sure!

The reason it's taken so long is that the ouside of the car (ie the bulkhead and floor) is completely dry, making me a bit baffled about finding the leak.

I should also clarify that my car is right hand drive and has a pantograph thingy for taking my pedal press across the car and into the back of the booster, which is in the same position whatever the drive hand of the car, hence my leak is into the passenger footwell and not the drivers.

So anyway, I plan on swapping the brake booster for a new one - unless someone knows of a seal kit I can get?

Final Q, if anyone's done this before and thinks there's something I should know before starting it, please let me know!

Thanks in advance,

Damian

[yaofeng]

Have never removed the brake booster. But I did loosen the booster linkage to fix the power steering hose connection behind it when the drive train was out. Don't know the accessibility of it with the engine in place. I'd imagine it'll be very tight. To remove the booster you'll have to loosen the aluminum bracket behind it. The bracket is attached to the car frame with a number of bolts.

http://i21.photobucket.com/albums/b274/yaofengchen/BMW_95_540/DSC_3149-1.jpg

http://i21.photobucket.com/albums/b274/yaofengchen/BMW_95_540/DSC_3148-1.jpg

[Kalevera]

I've never seen a RHD car, so for what it's worth --

Assuming the car uses the regular vacuum boost setup/ not a hydroboost system, the only fluid involved with the brake system is DOT 4, the vacuum booster ("brake bomb") is an air pressure differential, filled with nitrogen and sometimes regular air, no liquids.

I'm not sure how CHF or ATF is getting in the passenger footwell, the grommet passthroughs are sufficiently high up on the firewall to prevent any kind of fluid seepage unless the clutch master cylinder is leaking. This is an automatic car? Although a highly improbable possibility, I wonder if the car has a leaking line for the rear self leveling suspension, although I can't see how CHF/ATF would get through the firewall....

[yaofeng]

I've never seen a RHD car, so for what it's worth --

Assuming the car uses the regular vacuum boost setup/ not a hydroboost system, the only fluid involved with the brake system is DOT 4, the vacuum booster ("brake bomb") is an air pressure differential, filled with nitrogen and sometimes regular air, no liquids.

I'm not sure how CHF or ATF is getting in the passenger footwell, the grommet passthroughs are sufficiently high up on the firewall to prevent any kind of fluid seepage unless the clutch master cylinder is leaking. This is an automatic car? Although a highly improbable possibility, I wonder if the car has a leaking line for the rear self leveling suspension, although I can't see how CHF/ATF would get through the firewall....

I wasn't thinking. This is a very good point. I had a power steering leak in the brake booster area. That was why I loosened the booster bracket to get to the bottom of it. There are two power steering lines fluid (supply and return) behind the brake booster bracket. You may have a leak at the connection as I do. The brake booster bracket needs to be moved to the side to get to the lines and connections. The picture below is the hardline portion of the PS lines behind the bracket. It was a royal PITA to remove the hard line portion even with the engine removed.

http://i21.photobucket.com/albums/b274/yaofengchen/BMW_95_540/DSC_3150.jpg