Diffs, comms and rack 'n' roll

[niceguyteddy]

Ok......

Have had my X for a while (6 cells, bearings all round + bbcan) and am really happy with it. I have moved recently and found a cool un-used room in the ground floor of my building. It has a ruberised floor and the car behaves very well and has the space to 'stretch its legs'. GREAT.

After a few laps one sunday.... the car pulls up slowly and smoke is eminating from beneath the body!!! AARgh! I discovered the commutator has been completely melted, doh! Speedo seems ok. I then fitted an old stock 2wd type motor, the diff now slips alot unless it is tightened too much to function. Both diffs aswell. When stripped the larger balls seem smooth and the rings have a slight sheen to them were they touch the balls but not a groove. The smaller bearings(thrust?) are worse but seem ok. The diffs just slip too much, they were doing so in the final 4wd momments aswell.

Qs... (Finally)
Have the diffs simply worn out?

If so, is it the most likley reason the motor burnt out?

Anyone else with similar setup get through alot of diffs?

What lube do you guys use (I use Li based High temp general purpose auto lube)

Cheers peeps