Okay, after about a month of scrounging good used parts, waiting on new parts, waiting on the weather, and a multitude of other minor delays, my M46 and 3.31 rear axle swap is finally complete. After the first test drive yesterday, I am satisfied that everything works like it's supposed to and that there's nothing else that needs fixing in the immediate future.

While I was replacing the transmission, I also changed the clutch, clutch cable, transmission mount, 1 U-joint, parking brake shoes, and also a leaky cam cover gasket. All told, I spent just over $200 to go from a worn out old M45 and a 3.90 ratio rear to a much tighter M46 and a 1031 axle with 3.31 gears (with some fresh trailing arm bushings as an added bonus). The car now has a few less rattles and squeaks, and no longer needs to run at 3700rpm to do 60mph. Now I'm seeing about 2300 rpm to do 60mph with the overdrive switch engaged. The acceleration isn't what it was with the 3.90 rear, but it sure wasn't stellar before anyway. Besides, fuel economy was my main motivation and I'm willing to sacrifice the acceleration in favor of mileage. I've got another car that's all about acceleration for when I feel the need, so I'm quite happy with my transmission/axle swap project.

I also learned a few things during this project. My car is a 1980, and they didn't use a relay for the overdrive. The transmission I got was from a 1984 model which used a relay for the overdrive. The 4th gear switch from 1984 can't be used with no relay as it only has a single pin to interrupt the ground for the relay. 1980 wiring called for a 2 pin 4th gear switch to interrupt power to the OD solenoid. Instead of buying a new 2 pin switch, I merely used the reverse light switch from my old M45 transmission. Interchanges perfectly, and works flawlessly in this application. 1980 models must use a single pole, single throw switch inside the car to engage the overdrive solenoid when no relay is used. I mounted a rocker switch in one of the blank plates in the dash for my OD switch instead of the sliding switch on top of the shifter knob. I merely had to run a single wire from the fuse panel (fuse #11, for the overdrive) to the rocker switch, and another wire from the rocker switch and down through the shifter hole under the boot to the 4th gear switch. Later models with an overdrive relay used a momentary pushbutton switch to activate the latching relay for the overdrive.

Another thing that I learned (the hard way, unfortunately) is that Volvo used two different throwout bearings for non-turbo cars. I used the throwout bearing from the 1984 M46 with my old pressure plate, and the clutch would not disengage. That throwout bearing was at least 5/16" shorter than the one used in the 1980 M45. I also couldn't get the clutch cable to adjust properly with this throwout bearing in the car. I ended up having to drop the M46 from the car and put the old throwout bearing from the M45 (yes, I checked it carefully to make sure it was still good) in place, put the transmission back in, and worked it perfectly with the M45 throwout bearing in place.

If anybody has any questions regarding any part of this swap, feel free to contact me and I'll do my best to answer them.

billy242
1980 242DL with lots of GT and IPD goodies
original B21F now with M46 and 3.31 gears
1977 Datsun 280Z with 383 Chevy/700R4/3.54 gears
1967 Ford Fairlane 500 2 dr. sedan 289/C4/3.00 gears, 49k original miles