About a week ago I abruptly lost vacuum in my 83 240D (wouldn’t shut off, locks didn’t work, etc.). After determining that I didn’t have any obvious leaks or disconnected vacuum tubes, I searched this forum and figured that I probably had the piston type pump? I thought I would buy a vacuum gauge and do some testing this weekend and rebuild the pump if it was the problem. Yesterday I noticed the vacuum was returning slightly. Today everything is back to normal. My best guess since leaks don’t repair themselves is that a check valve must have hung up and/or had some debris in it. Well, I learned a long time ago that once something fails it almost always does it again. Does a check valve sound like a likely candidate? I saw a posting that these can be changed without removing the pump from the engine by taking the cover off with the pump in place. I’m hoping it works that way.

JohnM
1983 240D 4sp manual 150K

Sounds like the check valve to me. Mine was stuck in the port that goes to the brake booster hose.

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2001 Dodge Ram 2500 Cummins Turbo Diesel - 4x4, auto, 3.54 gears, long bed
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'92 300D 2.5 Turbodiesel - sold
'83 300D Turbodiesel - 4 speed manual/2.88 diff - sold
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'82 300D Turbodiesel - sold