I'm a Rc crawler guy as well as a drifter so i got a few tricks. First when you get the car take a look at the manual(if the car is a rtr or a prebuilt) then following the instructions remove the differential from the car and open it up. Now here's where my tricks come in: I like to take Locktite Sumo glue and put it on the two outer gears(the big flat round ones) You won't want to lock it if it's a ball diff you're dealing with, just make sure you tighten it so it gives you a locked diff feel but can still do it's job if need be.

Hope this helped, Nasher