Here are some questions answered about Diffs. I'm no super-expert on the subject (so if I have anything wrong, someone who knows better please feel free to correct any errors) but it seems worth mentioning this info for folks who don't know.
1. What's a Diff?
A "Diff" is short for Differential. Here's a picture of one for an XMods Evo (blue alloy)
2. Why is it called a Differential?
Because if you turn one side, the other side turns in the opposite direction. Here's a video I made to demonstrate this:
How a Diff Works
3. What's the purpose for it to be able to turn either side in opposite directions?
The video demonstration from question #2 only demonstrates how each side turns the other side in opposite directions. But when the Diff is actually in use, the Motor gear is driving the diff at the gears (not at the drive shaft that I was turning in the video). In doing this, it allows the 2 sides to turn at different speeds (another reason for it being called "Differntial"). This is useful for going around turns as it provides equal torque to both wheels (even though they might be turning at different speeds).
4. So then what's "Posi-Traction" or "Locking the Diff"?
Posi-Traction (or also called "Locking the Diff") is when you make a modification to the Diff that FORCES BOTH SIDES to turn in the same direction. This is usually achieved by simply using super-glue in the gears that turns either side in opposing directions. Thereby LOCKING the gears in position.
4a. Why the heck would I want to do that???!! Locking the Diff FORCES the diff to spin BOTH wheels equally. To many Off-Roaders this is a MUST mod. Whereas with a standard diff, if 1 wheel gets caught up then the other wheel will just keep spinning and you're basically stuck.
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