Hi, I have a 1986 Volvo 240. It has a button to push on the stick shift to put it in 5th gear. It drives and works fine except when I downshift from 5th gear. …then it seems confused and has a hard time getting back into gear, it kind of hesitates and lurches forward. It will not go into reverse after it has been in 5th gear until I turn off the ignition, and start it again.
On my 1983 245 there was a relay that screwed into the gearbox, accessible by raising the body a bit with a jack (and jackstands). You just need to create enough clearance between the body and the transmission to get a socket on it. I had to replace it because my manual transmission wouldn’t go into overdrive. If yours is the same, that’s the first place to check. If I recall correctly it was accessible from under the car on the passenger side. The othe place to check is the switch itself in the gear shifter. The cover pops off and it is easy to replace.
Go to a forum called Brickboard, rear wheel drive (RWD) section and search the forum. There you can learn everything you ever wanted to know about the Volvo overdrive relay. Another common problem is the wire that runs from the button on your shifter down through the shifter shaft. If you don’t find your answer, post a question on the Brickboard forum.