Shift/Vacuum Adjust
 

Having trouble understanding the two adjustable horizontal linkage rods above valve cover on '81 300D. I thought the front-most linkage, if lengthened, would cause earlier shift points. If so, fine.. then, what does the other one do?
Thanks, anyone.

I'm going through this right now myself. The one I'm working on has a problem with the valve on the IP I think, so I'm way off from where you are. It sounds like yours is much closer to being right.

I don't totally understand why there are two. One of them has a telescoping effect, maybe a damper inside.

I think you will find it helpful in understanding how this contraption works if you take off the black plastic cover on top of the valve cover.

To further understand what's happening, vacuum is supplied through an orifice at the vac booster line. As the throttle is moved, the vacuum switches underneath the black plastic cover bleed off the vacuum to decrease the vacuum as the throttle is pressed. This is supposed to simulate the vacuum of a gas engine.

Tee a vacuum gauge into the line that goes to the transmission. It should vary from about 15 or 20 at idle to between zero and two at full throttle.

Do a search and find my thread entitled "'81 300D Modulator" or something like that. There are two links in that thread that will provide extremely useful articles for you.

Good luck,

shift/vacuum adjust
 

Here is a link for Mercedes transmission adjustments:

http://www.mercedesdismantlers.com/AutomaticTransmissionInformation.html

Here is the link to the famous Steve Brotherton site...

http://www.continentalimports.com/ser_ic20242.html

Black box
 

Larry and Greg,

You guys say that black box on top of the valve cover also controls shifting? Mine is there and I fixed some broken lines when I bought the car but always thought it's only use was for EGR and cruise control. The shifting in my car has always been ok, cruise never worked, figured it was the computer control under the dash, and I have thought about removing the box because it's in the way of valve adjustment. Guess I may have to scrap that idea if it also tells the tranny when to shift.

Yes, the contraption on top of the valve cover is part of what "bleeds off" vacuum from the restricted source to simulate the vacuum that a gas engine makes. This in turn is used to signal the modulator valve on the transmission. It does also have something to do with the EGR valve.

Have a great day,