Is there a way to test out this W123 vacuum control valve (VCV) while it is out of the car? I have this one and I would like to know if it works correctly. Also, keep in mind that I'm not so savvy with this stuff so you'll really have to spell it out unfortunately. Thanks!

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Check the FSM for vacuum specs and apply that much vacuum. If it moves the lever it should work to shut down the engine. Check how long it takes to bleed down. That might give you an evaluation of the VCV unit. A quick check of the one on your car, if it works right, might give you a value to consider for the experiment.

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84 300SD
85 380SE
83 528e
95 318ic

The VCV is supposed to be adjusted on the car. You could use a mitivac to determine whether it has flow and also cuts vacuum as the lever moves.

Why do you ask?

You need to check the amount of vacuum the unit is allowing through, as supplied by your pump. The only way I know how to check and set it is while it is installed on the car.

And the procedure to do that requires a disc 20mm in diameter, with a 3mm center hole, 5mm thick.
Disconnect the linkage from the VCV to the IP,
Disconnect the black vacuum line going to the transmission modulator and plug in your gauge,
Put the special disc on the VCV stop pin,
Your reading should be between 5.5 and 6.5 inches of Hg.

Superior Transmission instructions for adjustment read as follows:
Pull the plastic bullet shaped dust cover cap off the side of the vacuum regulator. Using an 8mm wrench or small vice grip (depending on model of vacuum regulator) turn nut in approximately 2˚ increments checking your vacuum reading.
Clockwise = more vacuum = firmer shifts.
Counter Clockwise = less vacuum = softer shifts.
Note: Only 2˚ adjustments should be made at a time. Large adjustments can cause damage to the vacuum regulator.

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1982 300CD Petrol/Black Leather

I ask because I have an extra and I would like to know if it's in good working order. I bought it about a year ago because I was having some shifting problems but it turned out to be a vacuum leak. I figured I should keep this VCV as a backup.

How exactly would I test this with a mitivac? Sorry, I'm sure this is probably a rudimentary question but I'm a little confused by it all. I have a vacuum hand pump which I'm assuming will do the trick, right? I've attached a picture of it.

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1. I sincerely do appreciate your posting these detailed instructions. Quite valuable.
2. I just wonder (perhaps I am overlooking the obvious): Where would one find the appropriate disc that is, "20mm in diameter, with a 3mm center hole, 5mm thick."?
Given the precision of the instructions (e.g., 2˚ adjustments), it would seem that the disc's measurements require a high degree of precision - this is probably not some generic hardware store item.

If anyone would like to offer a source(s) for such a disc, that sure would be great.