W115 220 Master Cylinder Replacement Brake Booster / Servo - PeachParts Mercedes-Benz Forum

Coastal220 · #1 03-01-2013, 08:30 AM

Note: This is a taking off from my previous thread regarding white smoke at startup.

I have discovered that my master cylinder is leaking at the two rubber grommets attaching the reservoir. It is difficult to tell if the o-ring between the servo and master cylinder is bad, but there does appear to be the slightest hint of dampness where they meet, and the master cylinder itself has lost all its paint (I knew this when I bought the car but the latest leak appears new). I think I'll go ahead and replace the master cylinder and the o-ring just to rule this all out.

1) I've heard of some people getting bad ATE master cylinder units but this seems to be OE; current unit is ATE. Thoughts/suggestions?

2) Anyone know the o-ring size for master cylinder to servo? It seems like this should not be sourced from the hardware store as a cheap rubber o-ring.
From the pictures on Pelican the o-ring doesn't appear to be included with the ATE unit.

3) Should I do any maintenance/rebuild on the servo itself? I'd rather not pull it from the car as it seems to be functioning just fine.
Does anyone HAVE an extra one they would be willing to sell me cheap so I could do a complete and slow rebuild, new paint, etc? It's an ATE T51/909 ...like I need another project.

Mike D · #2 03-01-2013, 08:46 AM

Before you just start throwing money at a problem to "fix" it you need to diagnose it first.

Remove the nuts holding the master cylinder to the booster/servo. Slide the cylinder forward to inspect for leakage before you go replacing parts.

Have you recently added fluid to the reservoir and was an approved DOT 3/DOT 4 fluid, not a synthetic?

Coastal220 · #3 03-01-2013, 09:02 AM

Quote:

Originally Posted by Mike D

Before you just start throwing money at a problem to "fix" it you need to diagnose it first.

Remove the nuts holding the master cylinder to the booster/servo. Slide the cylinder forward to inspect for leakage before you go replacing parts.

Have you recently added fluid to the reservoir and was an approved DOT 3/DOT 4 fluid, not a synthetic?

Hi Mike,

All I've added was ATE Dot 4 to top the reservoir off, and I'm not noticing any significant loss in fluid.

It does not seem that the cylinder can be slid forward without removing the metal lines--everything is pretty locked in.

I'm not usually a fan of throwing money around but given the looks of the cylinder and the fact that it's fully rusted, the grommets will have to be replaced, and the metal lines removed to examine the seal, it's just peace of mind at this point. Not to mention brakes are pretty important. Plus I'll be able to toy with the old cylinder and perhaps rebuild it, have a spare on hand.

dirtyharry · #4 03-01-2013, 09:24 AM

Be Very careful when pulling the plastic reservoir out of the Master, it will break easily and is really annoying to replace. it is also possible your master is leaking into the booster, you can pull the master forward to clear the booster with the lines intact, then shine a light in there to look for brake fluid inside. I have seen this type of leak on several different Mercedes of this vintage. water has a tendency to drain under the booster running between the firewall and inner fender and rust the booster from the bottom, I think its more of a W108/109 problem but none the less you may actually want to pull the booster and see how solid it is. its really just 4 bolts on the inside, and the pedal has a fat bolt with a shoulder on it, very easy to pull on an automatic car.

Coastal220 · #5 03-01-2013, 09:41 AM

Thanks Guys, and for that smart advice Harry.

I'll try again to pull the cylinder forward. I may have been too gentle with it, or it may be rusted to the booster and need to be popped loose.

My vehicle is a manual, so I'll what I can do in the way of an interior inspection without opening it up.

Cheers

Coastal220 · #6 03-07-2013, 01:06 AM

I thought I would update this thread. I ordered a new ATE master cylinder from Pelican and discovered what looks like a manufacturer's oversight. The cylinder that extends into the brake booster is only partly machined, which in itself might not pose significant problems, but certainly calls their quality control into question. I know some brake boosters are designed with cast recesses in and around this area, but this, judging by the uneven appearance does not appear to be one of those cases. Anyone else seen anything like this? Is ATE putting a lot of questionable products out there?

For what it's worth, George at Pelican was very helpful and offered both an exchange and refund.

Bohlman200D · #7 05-24-2014, 11:58 AM

I'm glad you got this figured out. I'm a similar boat with my brake booster. Master cylinder has been replaced, have all the lines, and the pump on the engine is working properly. I stated losing vaccum power intermittently and then it just wouldn't work at all. It's very likely the brake booster itself, correct? I can't find one anywhere. Any advice would be very helpful! 1968 200 Deisel.

Topher39 · #8 05-24-2014, 03:08 PM

COASTAL - that brake master cylinder is normal, no need for that portion of the end to be machined. When I replaced my master cylinder it came with two rubber seals for the plastic reservoir to fit - it IS very difficult to get the reservoir out of the old and into the new master cylinder, especially with the new rubber seals the reservoir sits in. You can crack those nipples coming from the reservoir if your not careful. I lubed mine up and still had to trim off some of the nipple flange in order to fit. If it does crack, the plastic can be welded back together with heat. Just be careful.

Brake Booster Replacement - I got my brake booster from Rock Auto for $87, comes with a one year warranty. Make sure you check to make sure your Check Valve is working - if your check valve is leaking that would be an easy fix, easy to check too.

Chris