Had my new to me 84 300sd for a month and frankly am missing my 79 a bit. I have just begun to try to start sorting out its issues. The most serious is that the rpms will not go over 2000 to shift (except for when it flairs up to 3000 during the one to two shift). This is the same if the car is hot or cold. It basically behaves like gentle accelleration even when under hard accelleration. The only way to get the rpm's higher before the shift is to put it in D.
There are several vacuum lines missing. Two on top of the valve cover and one on the assembly near the master cylinder. Where are these things supposed to go to? And is this the source of my shifting woes? This car is getting a very dissapointing 21 mpg. which is 3 less than my 79 300sd.

Yep, that's your problem alright. There should be a vacuum line diagram on the core support on the driver side. You will need to get all those vacuum lines sorted out and you may even have to replace a vacuum switch or two under that plastic cover.

This whole contraption emulates the vacuum signal made by a gas engine. This will not be too expensive to fix unless the diaphragm on the back of the IP is bad. It is very expensive.

Good luck and Merry Christmas,

I dont follow you on that. I did find some diagrams in a search here but dont know what the heck Im looking at.
I did find a picture of an 84 300sd engine on e bay and it appears that things are routed correctly. The guy has a sightly different looking connection on top of the valve cover but has the same hoses as me going into it.
I also found that I have a hose that was broken indicated in the pic below. What is the name of that part that it connects to?
Is it possible the PO replaced the part on top of the valve cover with the incorrect part and that is why there are two open holes?

Attached Thumbnails

   

hmm, i would concentrate on the white vac valve on the IP if i were you. one line (black) goes into the car's cabin and connects to nothing and the other ones go to the tranny.
you can disconnect and block the ones coming from the top of the valve cover that go to the white valve on the IP

the line on the left on the valve cover should go to the egr which you can block off.

as for the second pic it looks like your boost valve. the broken line should go to the alda and the missing one to a banjo fitting on the back of the manifold. is the turbo working at all?

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1984 300D Turbo - 231k....totalled 11/30/07 RIP

The core support is the metal channel piece that runs across in front of the radiator. At the factory, they put a vacuum line diagram on there. It should still be there unless the car has been crashed requiring replacement or repainting of that structural member.

Good luck,

With the yellow line off there is NO boost, aka. SLOW. The nipple is broken off and the valve needs replacing. I suggest replacing it before trying anything else and the transmission might magically work again. Also do NOT connect anything to the nipple on top, it's a vent.



Vacuum Change-Over Valve

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Adam Lumsden
(83) 300D
Vice-President of the MBCA International Stars Section

ahh so the bottom vac line goes to the manifold ?,, it should be cleaned out anyhow to make sure it's clear.

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1984 300D Turbo - 231k....totalled 11/30/07 RIP