problems with the rear dif
 

i have a ofna mbx that is custum build to a truggy, and the rear dif keeps stripping the outer gear on the dif, it is like it whas from the factory, no whasers or any thing like it is from factory, any hints?

Sounds like the pinion and ring gear arent meshing very well, or the stock gears are a bit soft (non-hardened metal?)

I would try re-shimming the pinion gear to the ring gear (put some shims between the head of the pinion and the inner bearing), check there are no bad bearings alloying the diff to wiggle around too much, and look to see if there are optional harder gears, or an alloy diff case/cup (I have no clue on the design of the mbx, have a look in the buggy/truggy sub-forum for more ideas).

Best thing to do is buy a complete diff / bulk assy off ebay and then reshim it. The k series diffs with the bolt on ring gear are not the best, but if you shim them well they will last. As neil said get the pinion shimmed so that it meshes with the center of the ring gear, then shim the diff to fit snuggly against the pinion. If it feels a bit notchy that will be fine as the gears will wear together when you run it.

Link to part I mentioned : http://cgi.ebay.com/NEW-OFNA-ULTRA-L...3%3A1|294%3A30