Dissapearing Brake Fluid Mystery...
 

Last week the low brake fluid warning light started flashing, I checked and sure enough about 100ml was missing. I got down and dirty to look for leaking at the brake callipers but all was dry. Bone dry. When poking around the engine bay I spot the union of the brake cylinder vacuum pipe is loose at the engine end. I tighten it and top up the fluid.

Drive around for two days - no light, but when I pop the hood, the level has dropped again. Top up with about 60 ml of DOT 4, drive around town for a while and check. Its fallen again. I check the callipers and brake lines generally. Can't see any damp.

So whats the problem? Have I been topping up wrong causing a shortfall in the real level.

Should I have engine running and pump the brake pedal as I top up?

Or is the brake master on the way out?

Mike.

Master cylender leaking into brake booster. Remove the nuts holding the master cyl to the booster. Seperate them enough to look between them and see if you see brake fluid. If you do, I would recommend replacing both master cyl and booster as the break fluid can damage the booster and cause it to fail.

If brake fluid is leaking into the servo, it will get drawn into the engine and burnt. This will make the exhaust smoke grey.

No grey smoke yet! Sounds like a replacment job asap :(

Is brake booster the same as vacuum servo? There are two bolts, do I just loosen them and withdraw the master to take a peek?

Mike.

If you have a manual trans, check the clutch release hydraulic components, especially the slave cylinder.

The clutch release system draws fluid from near the top of the brake M/C reservoir rather than having a separate supply like most cars with hydraulic clutch release.

Duke

Duke thanks for the suggestion, I have a manual box so I'll check that.

I'm just looking at the Haynes manual. It notes to remove fluid from the "appropriate chamber" I was'nt aware there were 2 sections. Is the slave underneath the car?

Mike.

I should add the clutch action is perfectly good (apart from noisy release bearing).

Mike.

Check under the drivers side floor carpet, the master cylinder might be leaking inside the car.

??? Don't have a Haynes manual.

The clutch slave cylinder is just aft of the bell housing RH side as I recall If you don't know where it is you probably haven't been flushing the clutch system hydraulics along with the brakes. That will definitely shorten hydraulic component life.

Duke

I had a similar problem. It's pretty easy to simply loosen the two nuts holding the master cylinder to the brake vacuum booster. Pull the M.C. out just far enough so you can stick a wire into the booster like a dip stick. If it comes up "wet' with brake fluid you'll know where the fluid went.

I ended up replacing the master cylinder (it was leaking into the booster). I used a bunch of rags to soak up the fluid in the booster and get it dry. The booster on my 107 has never been replaced and it's been 8 years since it got drenched with brake fluid. It still works fine.

Don't let the brake fluid get on any painted surface, it's like a paint stripper.

Mike, just had this problem with my 300E. My slave cylinder had a slight leak, just barely put a sheen on the bottom of the bellhousing/transmission. Clutch action was normal. Removal and replacement was a bear, needed to approach the bolts with long extensions from behind the transmission. The hydraulic line needed a crowfoot wrench from below. Bleeding was easy, but somewhat messy using the reverse method MB specifies. I tried to suck the fluid out in the normal direction using vacuum, but no sucess, didn't remove all the air. Enjoy :-)

Okay here the latest, first I've had evidence of a small leak under the car for a while in fact i posted a thread

http://www.peachparts.com/shopforum/tech-help/87348-gasket.html

I thought it was a gasket but now I'm 99% sure its leaking brake fluid. I stuffed some paper towel between the undertray and the transmission where the leak seemed to be and an hour ago I pucked it out and its covered in fluid which is not engine oil or anything "heavy" or smelly. Given the location its almost cetainly from the slave cylinder. I checked under the carpet for a master leak but found nothing.

I topped up the fluid and drove home down a back road which meant fewer gear-changes. Sure enough only a tiny amount had been used.

Tomorrow I will call in a local garage where near where I work and get them to confirm one way or the other.

Mike.

As suggested its the slave cylinder, part ordered only about 30 euro. Job to be done Tuesday-ish!

Mike.