[jimmiprice]

Hi mate,
Is the car a new 2.0 model or one of the original 8ights ?
If its a 2.0 it will probably be the shimming on the rear diff that needs setting up.
If its a 1.0 model it may well be something i have had a problem with in the past. Last year at one of the nationals i melted the rear gearbox in one of my losi truggys. This was pretty extreme but you may of done something milder still causing some distortion.
If your confident the pinion and crownwheel along with the associated bearings are good check the four bolts that bolt the crownwheel on to the diff case are tightened down evenly. Build it back up and if thats still no good bite the bullet and buy a new diff case and gearbox case, only a tenner and that should sort it out. As i would guess for some reason the back of the car has been hot and something is out of line. If the car is a 2.0 and the shimming doesnt fix the diff problem do the same as ive said for the 1.0 car. Let me know how you get on.
Jimmi......