I know it's not a diesel but you guys are so helpful and I couldn't find anything in the tech or diesel forum searches.

The car is a 91 300SE. The owner brought it to me with the complaint that it would only occasionally upshift out of first. I found that the vacuum modulator was bad and replaced it today. Now it shifts perfectly in all gears except 4th. In 20 miles of city driving I got it into 4th once and it downshifted into 3rd after a minutes at a constant speed. It will not upshift into 4th under any condition, high RPM, light throttle, cold, warm, etc..

What is wrong, it's driving me nuts. All the other gears can't get much nicer.

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

Forgot to mention it has 80,000 miles on the car. He drove the car a week before buying it and it was fine, then a few days later the seller called and said the car wouldn't shift out of 1st. He made an offer and bought it for a cheaper price.

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

i have the same problem and my problem began when i changed
my driving habits... i heard someone say you need to floor these things.

so i started flooring the car.... and then this problem started... some times
i sooth my problem by adjusting the kickdown cable on top of the engine...

its a tuning issue between the modulator and the kickdown cable...

so you need to tune the modulator valve it should leak down to zero for
4th gear shift...

get a vaccum hose, 3 yards and geta vacum gauge and start driving..

I completely unpluged the modulator line and drove it, still no 4th gear, but all the other shifts were hard mechanical as they should be with the line unplugged.

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

when i loosened my kick down cable it started working for me..

but its still not perfect...my 4 does not work with zero vacuum as well..
i read for an older car you might need 2pt to make it work..

http://business.baylor.edu/Richard_Easley/autofaqs/main.htm

i found a great explination of this at the above web page with photos.

Kick down switch under gas peddle is stuck down.

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84 500 SEL (307,xxx miles)