How much back lash, oill weight and oil amount should be used in an 8.5 10 bolt for dirt track racing? I'm setting up a rear for my buddy but all I've ever done is street and drag race set ups.

Set the backlash to .008 +/- .001 if the gears are new. If they are used then go for .010 to .012. I would jack up the left side of the rear end a little and then fill it until oil runs out the fill hole. The oil tends to run up the right axle tube when going around in circles and the gears can run dry.

Thanks for the info.