Earlier this week I had a diaphram tear on my 300D's vacuum pump. Rebuilt it and reinstalled per normal.

This AM.... failed again. Tomorrow I will rebuild it, but is there some magic secret that I am missing. It is a pretty straightforward job, a PITA but straightforward.

Any thoughts, this is really getting to me.

JCD

Well , I am really just guessing ... and until you take it apart you won't know the exact cause of the failure THIS time.... if the diagram has ripped or if it involves the other mechanism....
Maybe you should describe what you did earlier in the week on rebuilding it...
Particularly how you made sure the piston stroke was at the proper place before you buttoned it up...

I removed the entire vacuum pump and disassembled it, cleaned it and reassembled it, replacing the diaphram. The valve/spring mechanism was in good shape, fairly new (about 1 year), I inspected it and reassembled.

The armeture fits against a circulating cam, as you know. Lucky or not, I have never had an issue replacing it with the orientation of the cam relative to the armeture inside the vacuum pump. It is flush when it comes off and flush when it goes on.

You are right, it could be another reason for the failure, however, my experience is that when the oil gauge flutters, I have now power breaks and the car won't shut off, it is the diaphram.

JCD

Before you remove the vacuum pump, remove the check valve on the top of the pump. You can do this with the pump on the engine. Failure of the check valve is probably the most common reason for "pump" failure. And it is easy and cheap to replace.

But I know it is the diaphram as it has evacuated some oil through the hose into the air cleaner.

Like MORE oil than normal or?
My engine spurts a little oil over there once and awhile...little blow by and whatnot..
curious.