My 10 year old C280 normally runs very, very smooth after the first 10 to 15 minutes. However, when cold, the transmission is not as smooth and sometimes gives a kick in the pants seat. It doesn't seem to be low on transmission fluid. Is this an early indicator of future transmission problems?

Also, what are the consequences of running regular octane gas vs the recommended premium gas? Can you alternate on fill ups at least?

The 1999 C280 has electronic transmission controls. MY 1st step would be changing the fluid. Fluid doesn't last forever as MB used to state!

They now recommend every 40K services & the fluid is better than the type used in your trans.


Under normal low speed driving the use of low octane fuel will have little to no effect.
BUT any time you need to merge OR ask for power the knock sensors wil retard the timing & power output will be lowered, that can also affect trans operation.
Never use E85 ethanol & try to keep fuel at 90 octane in the tank.

Trans computer needs torque info from engine to operate properly.

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I have the same trans in my '97 E420, and it used to slip out of gear, then slam back into gear, causing a "kick in the pant seat" as you describe.

My pressure regulator valve spring was broken. Replacement is cheap, and pretty easy. Requires dropping the pan and removing a plate on the side of the valve body.