Well heres the way the guys who drifts in south Fl at our sessions said to do it:
This isnt mine, i copied it from a reponce he gave me on another forum

Just to clarify, a ball diff is a ball diff. It doesn't matter whether it's in a belt driven car or a shaft driven car, the only difference is the pulley. A gear diff (which comes stock in the TT-01 kit) is something totally different. They both do the same thing, but are built differently.

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 a little rubbing alcohol to make them as clean as possible.


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



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



Tape side:



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



Hope this helps.
John