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Mercedes Benz 300D Shifting Problem

Q. Hello Vince, I purchased my 1984 Mercedes Benz 300D Turbo Diesel in the fall of 1983 and it did not begin having problems until 2002, so you are very correct in saying those particular models really hang in there! It currently has 143,000 miles. I had problems with power loss and replaced both fuel filters, plus had the Mercedes dealer adjust the valves.

Mercedes Benz 300D Shifting Problem

It seems to be running better, however, the automatic transmission is not shifting correctly. The transmission fluid level is correct, so I am wondering if there are other things I can check before having to consider major transmission repairs or replacement. The symptoms of the shifting problems are:

When starting off with the accelerator pressed and held to the floor, the transmission changes automatically from first gear to second as it has always done. However, I must ease up on the accelerator in order to get it to change from second to third and from third to fourth. That is no problem for me, but I wanted to let you know in case it sheds some light on the downshifting problem described next.

The car must be slowed down to between 20 and 25 mph before it will automatically downshift from fourth to third gear. it must be slowed down to below 20 mph to downshift from third to second , and be practically stopped to downshift into first gear. i used to be able to press down on the accelerator when going at slow speeds (ie. 30 to 40 mph) and the transmission would downshift to the correct gear to get the best acceleration power. now i must slam the accelerator to the floor to get it to downshift and when doing that, it always shifts to second gear. the only way to get it to downshift from fourth to third gear when going faster than 25 mph is to manually move the floor shift from “d” to “s”.>

So, do you have any suggestions of things I can check? Or, will the transmission need to be opened up by the Mercedes dealer to determine the problem?

I have done all of the maintenance over the years, changing all fluids in the car (including the transmission fluid and filter), replaced brake pads, and so on. So, I can do minor adjustments and repairs, if that is all that is needed. Otherwise, I will need to take it to the Mercedes repair shop for major repair work.

Thanks for any suggestions you may have regarding this problem.

A. It sounds like you have a shift modulation problem. Adjust your shift modulation cable to factory specs. An initial examination should reveal the cable to be loose with slack with the throttle in the idle position.

Additionally, if you transmission has never been flushed or had a filter replacement it maybe time to look into that as well.

Adjustment Of Cable Control For Control Pressure. Vehicles with engine 617.95.

  1. Push off ball socket (19).
  2. Push ball socket (19) first to the rear (opposite to direction of arrow), then pull carefully forward (direction of arrow) until a slight resistance is felt.
  3. In this position, hold ball socket (19) above ball head [drag lever (13) should rest against stop (14)).
  4. Adjust control pressure cable control at adjusting screw (15) in such a manner that the ball socket (19) can be pushed free of tension on ball head.

Mercedes Benz 300D Shifting Problem
Fuel Pump Module

Additional Information provided courtesy of ALLDATA

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