Our 87 240 was diagnosed as having a bad overdrive solenoid. (We were told a vibration which starts at 55mph and continues through 65 mph and greater is the result of our tranny staying in 3rd gear. RPM's are 3000 at 55mph and 3500 at 65 mph. Can rpm's at a certain speed tell you whether you are achieving overdrive? If a tranny was actually unable to move pass 3rd gear would there be a upper limit of mph that would seem normal to the driver. (Without the engine and tranny sounding or feeling unusual. We are not sure that the diagnosis is correct. We agree that the overdrive is not 100% because when the overdrive button on the shifter is depressed the od arrow displays on the dash but no change in the transmission occurs at any speed. We have several volvos which react abruptly when the od button is used on them. It seems if anything that the tranny is always ready for overdrive rather than unable to achieve overdrive. The other possibility is that the overdrive is always disengaged but the tranny does go to 55 mph very nicely and smooth. We changed the od solenoid with a used od no change. Not sure if the change was necessary. Still have vibration at 55 and greater. Like the song says "I can"t drive 55"

Thanx