leak between master cylinder and brake booster
 

Over the last 6 months I'vehad to add fluid to the brakes. Noticed that paint is peeling off the booster. I'm almost sure its from the master leaking around its push rod. Before I spend good money on a new master and a day installing is there anything else that could be causing loss of fluid and paint?

There is a Seal that is part of the Master Cylinder that when it goes bad can leak Brake Fluid into the Brake Booster.

If you think replacing the Master Cylinder is an issue. Some People say that if the Brake Fluid leaks into the Brake Booster the Brake Fluid can ruin the Brake Booster Diaphragm.

In any event to take a look you need do what is needed to move the Master Cylinder Forward to see if there is Bake Fluid inside of the Booster.

Less of a problem is if the Reservoir Seal in the back was leaking. But, you should be able to see that.

If you have a Manual Transmission the Clutch Cylinder uses Brake Fluid from the Reservoir.

For more detailed info:
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PeachPartsWiki: Do It Yourself Articles - Mercedes Vehicles

You don't mention what year and model you have so its a bit of guesswork for us.

Diesel911 mentions the clutch master because it can leak and reduce the brake fluid level in the rear portion of the mc.

In my experience changing the master cylinder is close to an hour job. If you have never done it perhaps two hours. I'll just say if you have not done it before be careful with the hard brake lines as it is easy to get them a little off straight in and if so it is hard to get the threads to start.

After changing it you will need to bleed the brake system.

If you find brake fluid in the booster it can be sucked out with a turkey baster. I have done this before and not had trouble but always worry that the brake fluid will damage the diaphragm but it has not so far as I know.

Use the correct recommended dot designation for the brake fluid.

Posted late last night, it's a 1982 240d. I've replaced a few master cyl in my life, its the bleeding process that gives me fits. Got tired of family members helping so bought a mighty vac, I've not had much luck with it.
Don't know what the picture in my first post is or how it got there. I didnt put it there.
Thanks for your help.

Mark

Picture is gone now. Wonder what that was all about.

A pressure bleeder works wonders.

Using a mity-vac should work as well.

How to Use a One-Man Brake Bleeder Kit | eHow

I have the Motive Pressure bleeder, and it works great on the MB. Has a cap that screws onto the MC reservoir.

I used the Mity Vac on my Datsun PU only because the universal adaptor I have for the Motive leaked. :( and there is no way the Motive will fit onto the tiny Clutch MC. The Mity Vac worked ok, but was more work and time.

The biggest problem I had with the MV was air being sucked around the bleed screw into my discharge container.


Charlie

I don't have the same brand of hand held vacuum Tester; but it works the same.

I only have the V Tester and it did not come with the brake bleeding reservoir. So I made one from a Jelly Jar and some plastic vacuum fittings and used Eopxy to hold them in place.

Anyway, it woks well for Me. I back off the Bleed Screw just enough so Fluid will pull through it. However, it is true that some Vacuum also gets sucked around it but in the end that does not matter.

You can be patient and keep pumping till Fluid comes once you see that the Fluid Level in the Master Cylinder is dropping you can simply walk away and let gravity do the job.

That is usually what I do and come back and check the Fluid Level in the Master Cylinder.

I also think that the fluid reservoir that comes with the Mighty Vac type tools for brake bleeding is too small as I like to bleed until I see clear fluid coming out.

this is where the motive power bleeder shines...

the fresh clean fluid is PUSHED through the system, keeping the MC full, bleeding all air out of IT and the lines. all positive pressure, no vacuum...

I have a Pressure Bleeder Cap that has a Gasket in it that needs to be replaced but I have never bothered to replace it or make a Make a Pressure Bleeder for it.

My only experience with a Pressure Bleeder is part of the Reason I was fired from a Mechanics Job.

My first time using a pressure Bleeder I assumed that the Bleeder was pressurize Air over the Fluid.

There was no Air Hose connected to it and I thought the Fluid was on the Bottom as you see in one of those Garden Sprayers that you pump.
What I did not know was that the Air Chamber was on the bottom with a Diaphragm between the Brake Fluid the Brake Fluid was on top.

I opened the top Valve to bleed off the Air Pressure and instead of Air pressurize Brake Fluid sprayed over about 10 Square Feet before I realized what had happen and turned it off.

It took a lot of that Cat Litter and sweeping to get that cleaned.

At the end of My probation time I was not hired and the only good things on My evaluation were that I showed up for work on time and I dressed OK for the Job.

Interesting story, bummer that happened. However it's worth noting that the Motive pressure bleeder most of us have used is not designed that way. Indeed, it is set up sort of like the garden sprayer you mention. Fluid sits at the bottom of the bottle and is drawn up in to the hose by the pressure differential you're creating between the bottle and the master cylinder. At some point the MC reservoir and the pressure bleeder hose are full and you continue to pump to build up pressure. This pressure pushes fluid through the system once you give it someplace to go (open a bleed screw).

The only downside I've found so far for the pressure bleeder, if you can call it one, is that it will help you find leaks by pushing pressurized brake fluid out. That is what lead me to replace the reservoir seals and float plugs per the guide I wrote on just that...I wasn't able to pressure bleed with the bad plugs despite the fact that the brakes worked fine still before the bleeding.

https://www.ifixit.com/Guide/Mercedes+W123+Brake+Reservoir+Rubber+Seals+Replacement/27809

The pressure bleeder helped you find leaks that it created by pressurizing portions of the system that are not normally pressurized.

^ Yeah and don't use too much pressure.

I replaced the float plugs on the CD.

The SD has different plugs, spring loaded.

Whatever helps draw attention to parts that have failed, I'm OK with. If you looked at the pictures, the plugs were in awful shape.

Regarding not using too much pressure, agreed, but in my case the float plugs started spraying fluid at about 3 psi...