How to Lock a Ball Diff
by John W.

Sometimes tightening the screw just isn't enough, so here's my method of locking Tamiya ball diffs:
 
1. Take the diff out of the car and disassemble into two halves. Remove the diff balls. Go ahead and wipe the grease off of the pulley and diff plates. Clean the diff plates with motor spray or some rubbing alcohol to make them as clean as possible.

2. Place a diff plate on a piece of electrical tape and cut off the excess. The tape is what keeps keeps the pulley from slipping. Do this for each plate.

-This is what one should look like when you're done:
Bare side:

Tape side:

3. Glue the diff plates to the diff plate housings with the tape side facing up and reassemble like normal, leaving out the diff balls. Make sure not to overtighten the diff screw.