Last month my 1986 300E would spontanesously down shift into 3rd, 2nd, 1st, and even neutral as I'm driving on the freeway at 50-60 mph.
I was told that it may be the Automatic transmission Filter, so I changed it (and the transmission fluid). The problem went away for a few weeks, but now it's back. Although this time I notice that the problem only occurs when the car has been driven around and the engine/tranny is warmed up. If I drive the car in the morning and let it cool off for a few hours then return home everything is fine. But if I'm driving the car around the whole day, the shifting problem occurs.
Note: The fluid levels are fine, and it doesn't smell burnt. The car ran fine until the transmission began to "act up". The car has 150,00 miles on it.
Any advice would be appreciated.