1994 540i Brake Master Cylinder - rebuild/cross reference

[JThomp33]

Hi BF- Did some digging online when my (EURO - HE62) 1994 540i didn’t pass its MOT. Long story short - rear of the brake master cylinder is leaking slightly - see photo:

725587

RealOEM and dealer confirmed PN is: 34311163924 and of course it’s NLA (and aftermarket seems to be no option as well). My two options seem to be:

Rebuild? - the rear seal seems to be the culprit and a company called FRENKIT make rebuild kits. I found on for the 34311162915 (rebuild kit 125093) but I’m not sure if the seal will be he right size. Does anyone have any input on a compatible kit?

Cross reference? - I’ve seen some E32 735i/750i will fit an E31 (PN 34311156643) which appears to be very similar in shape/size but I cannot confirm an exact match.

I am also trying to source a used part but any input would be greatly appreciated - especially if I can buy a kit for rebuilding.

Thanks!

~JT

[eddycooper]

Are you 100% sure that's the right part for you? I think that type of reservoir/master cylinder combination was on RHD cars. On LHD cars, the reservoir and master cylinder are separated by black plastic tubes.

If your car is actually RHD, then this thread could be helpful: https://www.bimmerforums.com/forum/showthread.php?1675021-RHD-540-question

[m60power]

JThomp33's car is a right hand drive UK 540i.

There's a chance that rebuild kit won't work, it looks like it's for the brake master cylinders powered by vacuum (air) assist, so not sure it would be the same as the master cylinders that are designed for hydraulic fluid assist, which from a quick search seems to be what RHD 540s might use, and similar to what early build date E32s use, but someone please correct me if I'm wrong. What is the build date of the car? What does the brake master cylinder bolt up to? Is it actually a hydraulic assist design?