I have a 1980 245 DL, VIN# *VC24545A1275444*, that I am getting back out on the road. I purchased the car over a year ago and have been working on some known problems:

1. All new bushings in rearend
2. New u-joints, center bearing and support
3. New cat-back exhaust
4. Heavy duty coil springs
5. New battery
6. Disassemble & clean fuel system, including intake manifold, throttle-body, etc
7. New O2 sensor
8. Inspect/flush rear brakes
9. Change differential gasket/fluid

The car handles much better now, passed emmissions and is nearly ready to drive daily. I do have new bushings and a brake flush/inspection for the front breaks on the schedule within the next couple of weeks.

Here's my problem. Sometimes at low speeds (just starting out), usually when in reverse, sometimes in forward, when I let out on the clutch, I hear a loud banging and the drive line feels like it might be in a bind. I inspected all of the work that I have done and see nothing out of place or loose. I have been able to observe the driveline while in motion in reverse and it does buck some. I can see the differential input dip down towards the ground in time with the bucking.

The previous owner put in a new clutch and said that he had it pretty well adjusted. I am going to make some minor adjustments to see if that helps. I also want to drain and refill the manual transmission. I do have an overdrive unit on this vehicle. The transmission ID plate is no longer rivited to the bottom of the transmission. I don't see ATF-OIL stamped near the fill hole, which lead me to believe that I have either older M41 or an M46 transmission. How can I tell for sure?

Also, if an M41, that requires SAE 30W or SAE 20W40, correct?
And, if an M46, SAE80W90 or SAE 80/90, correct?

Please help - the car is almost driveable, and I don't want to break anything!