My overdrive needs rebuilding, but I have not been able to find any one to reline the one way clutch. The car is very close to undrivable and if I rebuild the overdrive, I still won't have a car that I can depend on. My question is this: Did Volvo put a 5 speed in the later 240 series and, if so, what is involved in refitting it to my 81 model?

I would be pretty surprised if you couldn't find an M46 that was used, for as much or less than having someone rebuild the OD on the current one.

The M47 conversion is almost imposible, but not totally. You'd need a new rear axle with speed sensor (or parts to refit it to current). That in and of itself is impractical.

Then you have to diddle with putting in the electric speedo for the proper axle ratio, and wiring it into your current one. There may be some shortcuts somewhere here, but for the life of me, I haven't ever been able to find any possible way to do it other than to convert to an electric speedo. The M47II trans didn't have the ability to drive a manual cable speedometer as far as I know. This is one area where I'd say you could just score a later eighties parts car to switch the transmission out of. It isn't worth it. But the M46 transmission is pretty common in junkyards, although they do go through some of them because of OD problems.

Besides that, the M47 is like the later-eighties Audis. If you got a good one, you got a good one. But if it gave you a headache, it was a migraine.

i would not recommend putting a 5 speed (m47 transmission) in. they have a reputation of being a poor design. the m46 (four speed with overdrive) is much more reliable. I am drawing from experience of three m46 trans and one m47. the m47 started going bad at 120k mi.

My M47 is doing great at 151,xxx miles, but I know they can be hit or miss. It's still quiet and easy shifting, and it's never seen synthetic lube or overfilling, as far as I know. It had some hard driving when I was learning to drive stick a couple years ago, but I guess I didn't hurt the trans. I'll probably switch to Amsoil synthetic next spring (engine/trans/rear).

Some people have avoided problems with their M47's by slightly overfilling them with lube. Mine has 190k and works just fine. Redline MTL helps here as well, although mine had dino lube in it for the first 137k.

While the M46 is the champeen of sturdiness, it does also have all the overdrive issues (wiring, relays, etc) which the M47 does not.

Personally I like the simplicity of just shifting into 5th, but the last overdrive I used was in an 1800 a friend owned. That one took too long to shift.