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Old 11-01-2000, 05:18 PM
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Mr. BILL Mr. BILL is offline
Ghoulardi Rules!
Join Date: Aug 2000
Location: Austin, TX
Posts: 576
As reported earlier, mt '85 300D is showing sighns of vacuum problems. I purchased a MightyVac tester today. The pump is showing 23# at idle. Revving the engine effects little or no change.

Vacuum going into the shift module is around12# at idle and 15-16# revved.

Also, Pumping 20# of vacuum into the vacuum pump itself holds pretty steady. Seems to loose 1-2# after 5 minutes.

I removed the brake booster hose at the vac pump and could see the check valve. It looked kind of black and sooty (a technical term).

I've read posts by Benzmac that this valve can clog and fail.


1. Can I remove this by just wrenching off that fitting on top of the pump?

2. Can I clean this and with what?

3. Does Parts Shop sell a check valve?

4. Am I kidding myself this is the problem or does it sound more like a vacuum pump?

Thanks in advance!


90 300SE
85 300D
84 300SD (sold)
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