I just purchased a 1990 Mercedes 300SEL with 84,000 original miles. The car is in excellent shape, but the service history is unknown. I have only put about 1500 miles on the car so far and have been trying to catch up on all the maintenance items. The transmission has operated flawlessly for me until today. I was driving on the express way and took a clover leaf on ramp at a pretty good rate of speed, and suddenly I felt the transmission downshift into third. It wouldn’t up-shift back to fourth so I pulled off the express way and limped it toward home in second and third gear on the back roads. Suddenly after about 15 miles of back road driving the transmission up-shifted into fourth and now seems to be functioning properly in all gears again. The fluid level is perfect, but does look like it needs to be changed (and it was on my list). The fluid does not smell burnt or strange like there was any kind of additive in it. Any idea what could be going on?
Thanks for any and all ideas.

The "life" of rubber & teflon seals inside the trans are most likely at the heart of your transmissions problem.

You might try a bottle of trans "snake oil" like trans medic just after changing the fluid.

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sounds to me as though the inlet filter to the govenor is mostly blocked with crud.the valve bodies have to come down to fix it but i have seen several of these cars with the same complaint and this has fixed them.

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European Performance
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4696880422

"Fortune favors the prepared mind"
1987 Mercedes Benz 420SEL
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2000 Mercedes Benz C280
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Thank you David and MB Doc. Tonight I changed the transmission fluid and filter. The old fluid was very dark but did not smell burnt, and it was obviously in there for a long while. The pan showed no signs of metal or broken parts, and was relativly free of the grey clutch material I've seen in my other MB's. The filter material appeared really old and looked like it had very little flow. I cut the filter casing to have a closer look and the element was crumbling at my touch. After making sure the fluid level was close, but not overfull I took it for a 10 mile test drive. The transmission operated better then ever and shifted as it should. I'm hoping low flow caused my symptoms; but I'm still holding my breath. If the problem returns I'll get someone to have a look at those screens. I just don't feel comfortable going in that deep on my own.
Thanks again guys for your kind attention.
Outofspec

I am having an issue with the same MB722.315 tranny. When driving and accelerator pedal is quickly depressed for overtaking the box drops a single gear fine but if it has to for any reason drop 2 gears the engine revs come up to +/-5000rpm and the box will select second gear after which engine revs die completely, the engine appears to go into limp mode and wont rev past 1200rpm, almost as if the engine has over revved. the only way to reset the issue is to stop and turn the engine off and back on again and it drives as per normal. The tranny shifts beautifully up and down when driving normally this issue only occurs on a double downshift from 4-2