My 1990 300SEL (190k miles) seems to be developing tranny shift problems. Fluid and filter have about 15k miles - no leaks, odor, or burnt color.

The problem does not happen all the time and seems most likely after long drive - 30 minutes or more. If cruising down the highway and the accelerator is lifted, tranny downshifts into next gear and won't go back up unless car is slowed or stopped. Then it upshifts as usual. Wife just reported that while backing out of the driveway after a 2 hour trip, the tack raced a bit and it 'didn't feel right'.

So, looks like we've either got slippage or shifting problem. What to look for first? I'm thinking vacuum for the modulator? Any help appreciated.

Couldn't be the vac modulator, that only runs the "feel" (engagement speed of the shift, not timing).

Could be a loose or broken bowden cable, or a shorted or stuck kickdown switch (under the accelerator pedal).

However, this particular shifting behavior is often a valve body problem, requires serious work. Check the ease stuff first....

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!