[usetosellhummer]

some more jargin with t-case


An open diff is designed to allow the two wheels on the axle to turn at different rates during turns. As you may know, the outer wheel on the axle must turn faster than the inner wheel during cornering to cover the larger distance. An open diff allows this to happen with a set of smaller spider gears between the two axle shafts. . The down side is that it transmits power to the wheel that has the least resistance, or traction. This is good for normal, on pavement driving since it minimizes tire wear in turns, but In terms of off road performance, this is a bad thing. As soon as one tire starts slipping in the mud or sand, the tire that still has traction will stop receiving power. All of the power is sent to the spinning tire and unless you can add resistance to that spinning tire, you lose pushing power on that axle. If you spin a tire on both axles, you lose forward movement. Thus, with two open differentials you really only have a true 2wd system.

Limited slip devices:
LSD's are a step up from open diffs. These diffs use spring loaded clutch plates in addition to the spider gears of an open diff to transmit power to the axle shafts. when moving straight, the clutches allow the wheels to turn together normally. when one wheel wants to turn faster than the other, the clutches resist the faster wheel's movement. it must first overcome the friction on the clutch plates, which is a result of the spring force, before it can turn at a different speed. if the turn is sharp enough, the clutches will release, allowing the LSD to operate like an open diff for the duration of the turn. at the end of the turn, the clutches re-engage and keep the wheels turning at the same rate. Going back to our "stuck in the mud" scenario, the plus side to this setup is you still have a limited amount of power being transmitted to the tire that still has traction. until the amount of torque applied to that wheel can overcome the clutch friction, you still have forward movement on that tire. If you are stuck hard however, the amount of torque needed to move you forward can be more than the clutch friction and the clutches will break free on both tires, leaving you with an open diff. There is also the downside of having to replace the clutch plates every so often (~30K miles on some models) and that can get expensive. If the clutches wear out, you are left with an open diff. with an LSD, you have a psuedo 3wd or 4wd system (3wd if you have one axle with an LSD and an open diff on the other, 4wd if you have two LSD's). it's only a psuedo system because they can be defeated and rendered into an open diff in the right situation.

Lockers:
Lockers are the ultimate form of differential from a traction stand point. locked diffs do exactly what they sound like: they lock both wheels together so that they turn at exactly the same rate all the time. Unlike the LSD's, there is no defeating them short of breaking something. the tires will always turn together. a locked diff wll give you a "true" 3wd or 4wd system (1 or 2 lockers again) because all four wheels will always be turning even when there are tires that are slipping without traction. the only way you lose forwad movement is to lose traction at all 4 tires. Modern lockers now offer either a selectable option (you can turn them on or off as needed) or an automatic option. Auto lockers will still allow the wheels to turn at different rates during cornering so you don't totally lose the benefits of a diff on road but still retain the benefits of turning both wheels off road. Selectable lockers offer the benefit of open diffs on road and locked diffs off road at the touch of a button. There are two main types of lockers: lunchbox type, and full carrier lockers. the lunchbox style replaces the spider gears in the stock carrier. This means that the competent home mechanic can install one with basic tools without having to reset the complex measurements on the ring and pinion gears (on most vehicles). The down side is if your stock carriers are weak and some axles do have weak carriers. Be sure to check to see what axle you have and where it's weak points are before adding a lunchbox style locker (or any locker for that matter). The full carrier style locker replaces the stock carrier with the locker assembly itself. the ring gear is mounted to the locker itself, which is usually stonger than the stock carrier. This style however requires that the gears be reset by a professional mechanic and is usually best installed when regearing to account for larger tires or to achieve a lower crawling gear ratio so you don't pay for the gear reset twice. The benefit is a stronger axle due to beefier locker acting as the carrier. both styles do the same thing however.