The stock diff in the Slash is unsealed and filled with grease. There is a mod in XRC on how to seal the diff and fill it with Silicone. If I understand what you are asking, you would need to find a way to lock the diff. You can do this a couple of ways... some folks just put really heavy diff oil to help it slip a bit less... which would require you to seal the diff....some folks actually use JB weld to stop the gears from moving. If you don't mind me asking.. why do you want to stop the diff from slipping?