greetings, I have an 1988 240DL wagon Automatic. It has over 300K miles and runs awsome in every way, except it is not shifting up into 4th gear anymore. At first (6 months ago) it would shift up after it got warmed up, i would drive for 15 minutes on the highway in third, then it would go to 4th and be fine. then it took longer and longer to shift up and now it does not at all. it will run all day at 60 or 70 or more but won't kick up into 4th gear. the overdrive button worked fine before this and the light works correctly too. if it does go to 4th (once a month maybe) the button will bring it down to 3rd as it should. i have checked the fluid levels and they are fine. i'm thinking it may be a sticking valve or something. since the car only cost me $900 i'm looking for a repair that costs under 10% of that. any ideas? thanks for any help. Arlo

 

Maybe a bad Overdive relay or soleniod.