Losing brake fluid.

[ChrisSilva]

I noticed about a week and a half ago that my brake fluid resvoir was empty. I didn't have time to check that day. I filled it and yesterday tried to find time to look for a leak. I filled it again yesterday. I looked some for a leak, didn't find anything definitive. I think it may be leaking where the resivoir. Attaches to the master cylinder. I was wondering if there are any budget friendly ways to try to figure it out.

Thanks.

[02Pilot]

E34 is a vacuum booster, right? First place I check for mystery brake fluid loss is inside the booster - m/c seal fails, fluid fills up brake booster. If it's not that, clear the whole area thoroughly and then start watching closely. Obviously, the same goes for the calipers, though I'd say they are less likely suspects.

[bmwdirtracer]

Chris, I've got to tell you that "looked some for a leak" is totally insufficient, when you're talking about brake fluid. It is crucial that you find the leak immediately - this is not something you can put off, for a day or six.

Let's say, for instance, that your brake fluid is leaking from the grommets at the bottom of the reservoir, or, from a crack in the reservoir. You can actually replace these parts at home.

If the fluid's leaking into the reservoir as 02 suggests, well, you need a new master cylinder, and, almost certainly a new booster, because the diaphragm in the booster is not made to be in contact with brake fluid. If the brake fluid ruptures that diaphragm, suddenly you'll have no boost, and if you find this out when you really need to stop fast, you'll probably crash.....and then what's "budget friendly"?

Give any good Euro technician a half an hour and a lift, and he'll know exactly where your leak is.

Or you can crash....your call.

[ChrisSilva]

I'm guessing I need to remove the MC to check the booster? I'll probably clean the are around the MC, because we think that's where the leak is. I'm probably going to have to park it until I can figure all this out.

[bmwdirtracer]

When you've been filling it, have you spilled any? If so, that's going to make diagnosis more difficult. If you could find someone with a borescope, you could check the booster through the vacuum hose hole. These days, borescopes are getting pretty common.

[02Pilot]

Just dip a piece of something down through the vacuum hole (wire, weed eater nylon cord, whatever), taking care not to contact the diaphragm, touch bottom, and pull it back up. If it's wet at all, you found your problem (or at least one of them).

[ross1]

The clutch hydraulics on E34s are served by the brake fluid reservoir with the take off point being a bit higher than the bottom to prevent starving the brakes in the event of a leak. Include the clutch slave cylinder in your leak inspection. The clutch master can leak too but seldom does and would eventually drip on your shoes.