I have an 85 300SD that has had me puzzled for a while? Had a myriad of vacuum issues which I think that I have resolved for the most part, but am still mystified by what may possibly be my transmission. It shifts fairly hard and late in colder weather, along with running very poorly. When the climate is warmer, it runs and shifts considerably better but is still not what I would consider acceptable, especially in higher gears. Regardless of how long the trip and,or how long the engine has been running, performance doesn't change, which has led me to believe that it is possibly the transmission. The fluid levels are fine and is not discolored either. As odd as it may seem, does anyone know if there may be something which may expand and create a better seal or something to that effect as the temperature increases or any type of situation similar to this. Thanks.

 

the trasmission fluid do flow better and work better when the transmission is at "warm" operating temperature. When cold, you might notice the car holding a gear a tad longer and that is the car's way of warming up the system faster. At operating temperature, the shifts should be crisp but not harsh. Granted, the shift from first to second may be abrupt. And usually you might feel the shift from 2-3rd barely should it be noticable and the rest of the gears should barely be noticable unless you are specifically paying attention to it.

Now it could be that it is "adjusted" (not proper term) too tight, giving rise to hard shifts. When it's "adjusted" too loose, then you get mushy shifts.

Some people purposely adjust the transmission tight for harder shifts as they say it leads to better response but too tight and too loose have been found to lead to premature wear of the transmission internals.

Or it could be the wrong grade of fluid.


Transmissions on those cars really dont have too much of a overheating problem as they are almost about the same across the W126 line from the small engines to the big 560. And they are usually have a built in oil cooling lines that runs to the radiator for extra cooling.