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The gear teeth are cycloid or involute cut. Volvo probably made involute gear teeth, as they are much cheaper to make. I think Mercedes is the only auto manufacturer to use cycloid cut gear teeth. Cycloid cut teeth make for better mesh, but involute cut is easier to machine. Whether the teeth are cycloid or involute cut, the gears can be straight or helical design. Straight are stronger (no thrust), but beveled are much quieter. Chevrolet used some straight cut gear transmissions in the 1960s in their high performance V8 cars that were referred to as the "Rock Crusher" Muncie transmission. Those transmissions were stronger since there was no thrust with gear load, but you could hear one coming for blocks away. Just like reverse sounds in many manual transmission cars.
Volvo used red painted cast iron M46 transmission cases until about the 1986 model year, when they transitioned to aluminum M46 cases. In the 1988 model year Volvo changed to needle bearings for the M46 and M47 transmissions. I'll bet you are dealing with a cast iron M46 from a 240, prior to 1986. I doubt the iron case transmissions are painted with red lead paint. Red lead paint has been outlawed in the US since before 1980. There could be some lead in the paint, but as long as you don't make dust you'll be fine. Lead did make for really good paint, but that is another issue.
No matter which manufacturer, reverse gear is usually has bushings instead of bearings since reverse is used so little.
Early M46s had 3.71:1 first gear, later ones had 4.03:1. I think the split was about 1980. I knew, but have forgotten exactly when the change was made.
I've been doing this too long....
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john
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