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  #1  
Old 10-18-2011, 07:46 PM
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Join Date: Feb 2011
Location: Florida
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1984 W123 300D Transmission

Greetings to all. As the Subject line says I have the vehicle described and having a shifting issue. It is an AT. When placing the vehicle from park to reverse or drive it engages very rough and a bit violent. When going from 1st to 2nd gear it revs up high rpms before shifting violently. It is smooth from 2nd to 3rd, then will not shift into 4th w/o letting off the accelerator. I have adjusted the modulator valve (MV) one position ccw per some advisement taken from threads here and to no avail. I have purchased a new MV but wanted some some further insight or advice before replacing it. I have checked the AT fluid amount and added some lucas Trans. treatment to it and it's at the appropriate levels. I have not changed the filter. I am getting vacuum in the vehicle but not sure if it's reaching the MV.

Thanks to all for reading.

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1984 300D Turbo
1984 300TD Wagon
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  #2  
Old 10-18-2011, 09:13 PM
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Location: Carson City, NV
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You are on the right track. I am almost certain you have a vacuum issue, as in no or not enough vacuum reaching the modulator. It's best to start by checking for vacuum at the modulator with the engine at idle. If you don't find it, or enough of it there, start going up the line component by component until you find the problem. There are (or were) some diagrams of the system posted on this forum somewhere. If you can't find them, I have some saved to my hard drive.
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83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
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  #3  
Old 10-18-2011, 11:54 PM
1985 300D Turbo
 
Join Date: Feb 2010
Location: Florida
Posts: 628
Bowden cable

You have a cable that is called a bowden cable that will adjust when the transmission shifts. Playing with that adjustment should yield some good results. Be careful turning this plastic screw as it is probably over 20 years old and brittle. Usually it is on top of the valve cover and has a rubber boot over the cable. In figure 6 of this article is a picture of the bowden cable, hope this helps

Does your car have the blue flying saucer? Usually on the drivers side fender well. More than likely that thing is not working (if you have one) and can be bypassed. Vacuum issues can cause shift problems too. The modulator on the transmission cannot really be tested until you remove it from the car. I had the original in mine and the rubber was really stiff in mine causing harsh shifts. Once that was replaced and the bowden cable was adjusted, and the blue flying saucer was bypassed it made a world of difference. Now to turn up the ALDA!

PeachPartsWiki: MERCEDES-BENZ TRANSMISSION
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  #4  
Old 10-28-2011, 10:25 PM
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Thank you for your replies. I have adjusted the bowden cable and seems to be getting me closer. I think once I get the MV tweaked it may all come together.

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