My guess is dissimilar materials would make for a poor combo in a diff, I suspect the plastics would chew quickly working against metal.


Titanium would be nice, but then you can bet it would be expensive.

Why not alloy?, my guess is cost, cast plastic can ok, as can cast steel, cast alloy is traditionally soft, you'd need machined alloy gears, which I'd guess would be expensive, like machined titanium, nice but would you pay for them?.