Unfortunate Brake Leak

[Peter303]

So I've been lurking around the website for years and the faqs have gotten us through numerous fixes and adjustments on our 81' 528i. Sadly an automatic but dependable for 3 years so far. So had a minor break leak that turned major and rebuilt one front caliper 2 years ago.

A apparently new brake leak started to be an issue recently so we decided to rebuild all the calipers, did the two back ones first. Leak has gotten worse but isn't in the new work. In fact really going over the engine compartment with a new light found the leak and its probably been work slowly the whole time. Doesn't appear to be the master cylinder or the brake booster are leaking but a mysterious little cylinder interrupting just one of the front brake hard lines and mounted directly under the brake booster toward the fender from what I think is the power steering.

What is this thing? Either it or one of the fittings going into is now leaking even better with the back calipers rebuilt, but over the however long it was leaking more slowly it did a number on all the paint and coating round it as well as for a way along the bottom of the car. If its just a fitting it seems like the easiest access could be gained by removing the brake booster and master cylinder but if this "thing" it self is leaking I'd like to know what it is to replace it. Is pulling off the master cylinder and booster in one piece straightforward?

Thanks,
Peter D.

[Keith]

I had the same thing on my '79. That mysterious part you speak of is the brake pressure regulator for the rear brakes. Mine was leaking from the zinc plated diaphragm every time the system was pressurized. It can be removed with a little effort (mine brake lines were stuck pretty well) and replaced. The part number is 34341110092. They're a little pricey, I think mine was around $109 from
http://www.mercedes170-171partsstore.co ... eries.html
Check out the site. It has pictures of the part so you can compare it with yours and see if it's what you need.