As I am testing the vacuum lines going from the top of the vacuum pump "downstream", at what point am I to see the ~15 read versus the 25 or so I get at the pump?

OK- I am gonna go with " after the VCV" and the vacuum damper thingy. Since it takes about a minute for the VP to generate the requisite vacuum level throughout the system, what would prevent the transmission from hard shifting upon take-off?

I know that you should see around 15" after the damper that is connected to the blue flying saucer that goes directly to the trans. Not sure what kinds of readings you would get between the BFS and the VCV, pump, etc. This is basically the final reading that the trans is getting, so I'd say it's really all you need. From there you can determine if something else is at fault, should you not get a reading in the vicinity of 15" (say, 12-17)

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Dan
2005 E320 CDI - 246k
1987 300SDL TD05-16g, Herlevi pump, Elbe manifold, 2.47 LSD - 213k
Past: 1987 300D - 264k

awsrock- thanks for the reply. I do get ~ 17 at the line going to the transmission. Now, what about the question of the time delay from having no vacuum at the start and what is the standard time for the VP to get things going?

The vacuum pump should have the levels correct within 30 seconds. I have an "economy" gauge from a gasser cluster installed in my '87 300D (W124, OM603) as a monitor on the transmission vacuum line. Let me go start the (cold) engine, see how long it takes to build up vacuum.

[please wait]

OK, here are the results. Conditions: cold engine, not driven for 18 hours. Outside temperature, 70F. Pre-glow time: 10 seconds. Start engine and idle, watching after-glow light and "economy" [vacuum] gauge.

Results: vacuum reaches 80% of final value by the time the after-glow light goes out (20 seconds after starting engine). After this time, the vacuum level gradually increases to full value in a couple of minutes. Adding a little footfeed speeds up this process. I suspect that I have a tiny vacuum leak that contributes to this delay.

Opinion: you should have enough vacuum to drive the car without transmission clunking within 30 seconds of starting the engine. If you do not, there is a leak somewhere or the vacuum pump itself is worn/damaged.

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

thanks Jeremy 5848, as always classy and full out attempt to help my many times misguided attempts of understanding what makes my car "tick".... I had installed a new VP a few weeks ago since there were so many posts urging to switch out of the old style before it goes kaput. For some reason I thought that a new pump would create the vacuum levels much quicker than the old one.... Thanks again!