RE: How to lock diff?
Here check out these tutorials, they may help:
[link=http://www.rcdrift.org/forums/viewtopic.php?t=105]Locking a rear diff[/link]
[link=http://www.rcdrift.org/forums/viewtopic.php?t=1481]Locking a rear diff - HPI Sprint Style[/link]
[link=http://www.rcdrift.org/forums/viewtopic.php?t=3439]Locking Diff - Yokomo MR4TC SD Drift kit - Tutorial[/link]