[Serum]

One hopup i advise to you is the g-maxx single speed conversion (weightsaver too) And an aluminum diffcup and diffhousing. When these are shimmed right, they are very tough. (stock gears)

The older stock gears are not as tough as the new traxxas gears.

And indeed, shimming is done to reduce play to a minimum. The goal is to let the gears touch eachother as much as possible without binding.. (that's the art of proper shimming)

And with the plastic cups there is just too much flex possible, so the gears can create their own play.. And when the play is created, the contact is needed the most.. (under large stress)