ok, i know what an open differential is, and i know that locking differentials allow you to spin both wheels, but whats the difference between that and a limited slip, or a posi, or trac-lock? i thought they all pretty much did the same thing. someone please teach me!

 

Donate54,

There are plenty of threads on this. The more recent ones involve me asking the same questions. You can probably get all your questions answered there.

Re the locker (other than ARB) - usually involves REMOVAL of the spider gears (i.e. no more walkaround torque transfer loss). With things like Detroit Lockers, when stuck the "unstuck" wheel will still get 50% of the torque (or really 100% of usable torque, but that's an esoteric issue). When turning a corner, the locker disengages COMPLETELY. The outside wheel that turns faster gets NO torque. Thus the propensity for the truck to either spin wildly or suddenly straighted out if you throttle through a turn. Also there typically is noisy engagement/disengagement of the locker (although I've heard the Powertrax has solved that).

Re the lsd - usually involves clutch MODIFICATION (not removal)of the spider gear/side gear arrangement (i.e. there is walkaround, there just has to be enough force to overcome the clutches and "force" the walkaround). Obviously, if there is walkaround (limited as it is) by the spider gears you will not get a 50/50 split like with a locker (torque will be wasted in the "slip"). But the point is that the "unstuck" wheel will receive a reasonable amount of torque because of the friction resisitance offered by the clutches that are slipping (i.e. torque bias is now greater than 1:1). When turning a corner, the outside wheel does receive some torque, although the inside wheel receives the majority. Thus the better handling of the limited slip on the street (although you still have a propensity to fishtail moreso than with an open diff). Engagement and disengagement is also not as noticeable as with a locker.

 

People use the term "Posi" to generically mean a differential that drives with both wheels. "Posi" actually refers to the GM trademarked Posi-traction. The limited slip is one of the many traction devices available. Ford calls their limited slip differential the Trac-lok, which is what is available from the factory in F-150s. There are several methods that differential manufacturers use to drive both wheels. You can get the exact way that they work by viewing their websites. You could try Auburn, Eaton, Torsen, or do a general browser search. Many have nice overviews like www.tractech.com

 

thanks for the info guys, very informative!