While working on my brakes, I decided to check the vacum pump pressure.

At the brake booster (with all the other lines plugged up) I'm getting about 24 to 25 PSI at idle. But, in the Haines manual, it says that vacum should increase as the engine RPMs increase. My vacum remains static, however, not changing at all as the engine speeds increase.

I also have some vacum related problems I am trying to diagnose so I wonder if I need to start at the pump with a rebuild or replacement?

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1987 300TD
1985 300TD (sold)
1980 300TD (sold)
1972 280SE 4.5 (sold)