'78 300SD

[Jim W.]

We have a 1978 300SD that has very little vacuum.  The fuel shut-off will not work by vacuum, there is little initial brake boost when first pressing on the pedal, the doors lock but slowly, the trunk will lock even more slowly and the fuel door lock pin is making progress toward locking.  I have used our MityVac hand pump for a vacuum test on the vacuum pump and we have about 3.5 in. hg.  This test was done on the line from the pump to the brake booster by disconnecting the line at the brake booster and testing the vacuum generated in the line.  I also pumped 22 in. hg at the brake booster that held for several minutes without a loss of any vacuum.

The symptoms seem to point to a vacuum pump that is not functioning adequately.  To repair the pump I would like to get a repair kit but am having problems finding the correct pump or kit.

My questions are:  Am I on the correct line of diagosis for the lack of vacuum?  And, where can I find the correct pump and repair kit for the 1978 300SD?

Jim W.

[The Warden]

Sounds to me like you've correctly diagnosed a bad vacuum pump.

I've had pretty good luck with parts from this site: http://catalog.mercedesshop.com/ If they don't show the pump that your car has, call Phil...they stock more parts than the website shows.

Hope this helps some...good luck, and welcome aboard!

[Jim W.]

Thank you.  Will follow your recommendations.

Jim W.