I have a 1985 Mercedes 300D Turbo, which is Automatic, and when the transmission shifts into first and second gear, the car jerks (unless you let go of the gas pedal) which gets annoying, I do not know why it does that but I think that I should change my transmission maybe? Anyone know what I should do? Thanks!

Search this forum for info. There are 3 possible adjustments for the transmission. Bowden cable , Modulator and the vacuum control valve. My '82 300D does the same thing. I've been able to make it shift easier but I'm still in the tweaking stage.

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At this point certainly not. Just start reading everything you can about the transmission in the archives. I believe your complaint is common and usually fairly easy to rectify.
Also there is a very good thread on site about how to do all the required vacuum tests. The transmission is somewhat vacuum controlled. Basically you are describing hard shifts. Again a fairly normal complaint not usually requiring a transmission change or rebuild.

The vacuum system on these cars controls shift quaility, i.e. hard or soft. Usually when you have a leak in the vac system the transmission start to shift hard. So make sure you vac system is all sealed up. Once the vac system is sealed then you can start adjusting the transmission modulator which is what control the harness and softness of the shifts.

The bowden cable adjusts the RPM at which the transmission shifts. My wagon's bowden cable was way out of adjustment when I bought it. I adjusted it and it helped imensely.

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