Tried to get get the overdrive working on my sons newly aquired '85 240. Before I started messing with it, the main transmission worked great. After installing a new switch on gear lever the sytstem worked well enough to hear click of solonoid and activate light on dash. When we tried to use O.D on highway it would not engage, and car began to "freewheel" when coasting. That is, all braking effort normally provide by motor was gone and tach would drop to idle speed when foot was taken of off gas pedal. A change of transmission fluid revealed the round high pressure filter was full of gunk and partially collapsed. Replaced filter and reassembled but sorry to report car still "freewheels". It seems to do this when hot and work fine at start up. At times reverse gear does not engage with-out several attempts. Looks to me like I need to replace unit?? Any ideas appreciated!!