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Discussion Starter #1
Last year I picked up an immaculate 81 300D. Recently the transmission is shifting hard, & sometimes seems to want to almost double clutch.

I've read many threads on it. I've checked vacuum, the line going to the transmission has a vacuum reading of 7 when at high RPMs, & 17 when at lower RPMs. I read somewhere where this should go from 10 to 0 (idle to high RPMs), is this too high? I've swapped the green pressure regulator from my 83 that shifts fine, & it still shifts hard. It seems to also rev higher before shifting.

I've replaced the plastic levers on the 3 three-way vacuum switches on top of the valve cover. Vacuum has always been good on this car. Transmission oil level is fine. I'm going to be swapping my switchover valve between the two cars next.

Any suggestions? I've got the MB service CD, but I can't find the vacuum diagram on there. Also, having 3 valves on top of the valve cover is odd, I've only seen 2 on my other 300D's. Anyone have a diagram of the vacuum lines for that year?

Any recommendations? It's my wife's daily car, & she's getting a bit upset with it and me!
Thanks
-tony
 

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Answering my own question. It was the switchover valve by the injection pump. Swapped it out tonight & transmission was smooth again. Not perfect, but 990% better.

I'm still curious to find a vacuum diagram for that car. But at least it's running smooth again for now!

-tony
 

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TexasTony

What does the switchover valve near the injection pump look like? Do you have photo of it?

Thanks
I had a 1981 300D and it is the total vacuum shifting was godawful worst system they ever built which any MB mechanic will tell you. I replaced all of the parts eventually and got it so it was pretty good. I spent $50 with a MB mechanic who said my repair was as good as he could get it. When the tranny blows up which it will sooner than you think, put in a 4 speed from a 240D from a junkyard(accumulate the parts now).Do not make the mistake of throwing in a rebuilt tranny in that year!!!
 

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Discussion Starter #6
For a picture, see 617 Turbo Diesel Transmission Vacuum Shifting Valve (used) | MercedesSource.com .

Note, I replaced it & the transmission was shifting as smooth as a baby. Fast forward a week or two, & it's acting up again. I haven't even gotten the replacement valve to put into my car yet!

Yeah, I've heard that these '81 transmissions aren't worth a hoot. Darn if I don't have 2 81's! And I took the valve off my 83... :(

Oh well!

-tony
 
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