Tubber - I am experiencing similar vacuum problems on an '85 300D but the vacuum pump has been operating for at least 3 years. Were you ever able to determine the "correct" vacuum reading at idle? At 850 RPM is see about 5" and steady as measured at either of the small outlets near the check valve. As RPMs increase it goes up to 11" but is is VERY erratic. I disconnected the vacuum boost line just above the vacuum pump and measured wildly erratic (rapidly fluctuating between 4" and 22") at idle. I need to figure out if a pump rebuild is required or if these erratic reading are acceptable. My concern comes from the fact that it is now taking several seconds to operate the door locks and to get the engine to stop. These used to be almost instant. I never measured the vacuum when everything was working and I can't seem to locate acceptable vacuum readings.

Thanks for the suggstions,

I believe my origial thread stated that I just finished rebuilding the pump with a new kit (new check valves, everything) Reading through past posts, I discovered some had problems with their check valve O-rings which came with the kit. I checked mine with the originals and found them to be the same size/thickness. I have measured the vacuum right at the top of the pump with the metal line disconnected from it. My vacuum is very sporadic, bouncing rapidly from 0-20-25 Hg. Is there anyone that has checked vacuum right at the pump and what does it read? Does it bounce, or does it read a constant reading?
No, my locks do not work, I want to address the pump BEFORE I move onto other issues. Right now, the lock line is plugged with a golf tee.
I haven't addressed any other vacuum lines etc or brake booster yet because I figure its not worth it if the source of the vacuum; the pump isn't working properly and I haven't been able to establish that here yet, or a reason why it wouldn't be operating properly after a rebuild.

I still don't know what way the check valves are supposed to be oriented. If they are oriented properly, what other issues could be the problem? I do take blame for this, I should have paid closer attention on the tear down of the pump initially, so now I turn to this forum to help me. With the pump cover off, the two face towards me, and the single check valve faces down. "Faces" is referred to the valve resembling a type of bowl, and the bowl is the face. Make sense?

Anyone?

Thanks

Blaine

I cant tell by inspection . Which way do the 2 check valves go? I have the same pump and can not remember how the check valves came out. Thanks for your help.

The check valves go , the two together crown down, the 1 alone crown up, the torque on the piston lock nut is 9nm and on the pivot shaft nut 8-10nm. If you have trouble with the piston seal, you can heat the body of the pump with a heat gun until it sweels enough to slide the assembled piston in.
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blindwolf
1983 300D

Is the one down leading to the air filter? If so that might answer my question for the earlier model with only two valves.