If you are lucky, than your problem may be a plugged orifice in the vacuum pump. I had the exact same symptoms on my '83 300Sd, and that's what it was.

At the Vacuum pump end, remove the large vacuum hose that runs from the pump to the Power Break Booster. Look closely at the little orifice that's there and see if its plugged. If so, remove the blockage. If not, keep on troubleshooting


Phil

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'95 E300 Diesel, 264,000 Miles. [Sold it]