Im changing my front and rear diff fluid, and was wondering if i need to add any limited slip additive? Ill be using mobil 1 75-w 90, also wheres a good place to get a torque wrench? is the torque wrench a must?

 

How much are you willing to spend on a torque wrench? IMO, Sears Craftsman are a good mid-range tool. Snap-on and Mac are top-tier, and top $$$. I decided that, for as much as I use a torque wrench, to go the cheap route and ordered this one from TireRack.com at $29.99.

Sorry, I can't help with the LS additive question. I have a feeling that most folks are going to recommend Royal Purple or Amsoil over the Mobil 1.

 

No limited slip additive is needed on our diffs, which are a gear driven variety. No clutch packs inside = no LS additive.