Well, I think the most comman way with 1/10 scales is a hex, or some type of hub on the spur gear shaft. Then there is a disc on this hub, and when you apply brakes, two plates squeeze on the disc forcing the spur to slow down and/or stop.
If you look at a thread, in this forum about an unusual brake problem. That thread has some pictures that might help you get a better idea of what I'm talking about.

IBrakeForNobody is trying to figure out brakes eh?