Well, my '85 300SD has been getting some long awaited TLC. Latest in a round of fixes was the vacuum line connections and vacuum elements and such. I've been corresponding with Mercedes Source about a rebuild kit for this thing. With only the brake booster in the circuit, I would get a max of 18"Hg on my tester. They said to isolate the pump by itself and retest. Last night I couldn't so I thought I'd do it at lunch today. Hah!

On the way in to work, about a 25 mile drive, the brakes started getting harder and harder. I had removed one of the vacuum elements last night and had my tester plugged as something to prevent another vacuum leak. I looked over at the tester and 3"Hg. The next time I looked at it, doing 60mph, 0"Hg. Next stop was a white knuckle stop. I felt like Fred Flinstone trying to stop this thing with my bear feet through the floor board.

I eased into the office and parked in the garage. Turned the key off, and you guessed it nothing happened. Opened the hood, hit the STOP lever and it wouldn't kill it either. I hit it as hard and as fast as I could. Nothing. Linkage thing here I guess. I pulled the vacuum tester, started going throught the lines on the injection pump until at last, blah. It shut down. Oh yeah, BTW did I mention that it's snowing like crazy here and was all the way in.

It's a good thing I had Buck, my guardian angel with me. Wheeew!

I've been there......nothing worse than that "I KNOW I'm not going to stop and where do I go" feeling.

Rebuilding the vacuum pump is not too complicated. I found that if you take off the front end of the pump, you can replace the diaphram and the valves. I removed the fan and fan shroud as well to help with access. All in all about a 2 hour job if you go nice and slow.

Just remember that the valves are spring loaded and keep track of how they were oriented. In addition, use loctite blue when putting it all back together.

Good luck

JCD

JCD, I noticed in your sig. that you are driving a '77. Does that model have the round vacuum pump with a single large diaphram? Mine is a newer style pump and they (Mercedes source) were pretty sure it was a pump-off rebuild. I asked just because I was trying to avoid another oily mess. Have you done one this style?

Thanks for the input.
Tim

Sorry, wasn't paying attention. I do have the round one, W123, and have no experience with the 126.

Maybe a search is in order or a new post.

Good luck and glad you made it home safely.

JCD

Actually all the early 300D's up to or thru about 1980 have the round vacuum pump like the W115 220-D's and 240-D's. The later 300D's should have the piston type like the W126's. The round ones are fairly easy to repair, but have not done one of the piston ones yet so can't compare the difficulty level.

__________________
1961 190Db retired
1968 220D/8 325,000
1983 300D 164,150