Mcleon6494

Hi all, I have a 1983 Mercedes-Benz 300SD with around 170,000 miles and I'm having transmission problems. It's the 4 speed auto, and has trouble shifting into fourth and third gears (especially 4th, but 3rd is acting up now as well). I'm not the most knowledgeable with these cars, but I feel like it is related to the vacuum system.

When it's cold the car seems to shift just fine up into the higher gears, but as it warms up it begins to get finicky with fourth and then third. I had been able to get it into those gears by shifting into neutral then back into drive, but today it was not working. Along with this, selecting "3" would not shift the car into third gear from second even at redline.

Any information about this would be beneficial, thanks!

Plutoe

Post your VIN!!

OM617.95

Screw off with that VIN BS! YOU DO NOT NEED IT!

First off, vacuum has nothing to do with when the transmission shifts. Vacuum only controls how hard/soft the shifts are.
The bowden cable (throttle valve cable) on top of the valve cover controls when the transmission shifts.

How is power? If the engine is low on performance then the increased throttle needed to make the expected power will cause the transmission to shift at higher RPM. If the engine is getting high throttle input but can't reach high RPM then the transmission will not upshift.
The easy way to tell is to disconnect the bowden cable. It should upshift very early and reach 4th gear no later than 25mph.

When is the last time the ATF was changed? If the filter is plugged then the valve body will be starved of oil and can't feed the clutch packs and band pistons.