Differentials
Trak-lok (aka Posi)
The spring pack pushes the side gears against the clutches, which are attached to the cage. Both side gears spin with the cage when both wheels are moving at the same speed, and the clutches aren't really needed -- the only time the clutches step in is when something happens to make one wheel spin faster than the other, as in a turn. The clutches fight this behavior, wanting both wheels to go the same speed. If one wheel wants to spin faster than the other, it must first overpower the clutch. The stiffness of the springs combined with the friction of the clutch determine how much torque it takes to overpower it
Code’s Info
The Ford Racing Traction-lok is a great differential that is on many 10 second cars. The Eaton unit is the Ford Traction-lok but packed with more clutch packs to make it stronger. Also, the F-150 is the same Traction-lok as the Ford Racing Traction-lok.
Locker
The locking differential is useful for serious off-road vehicles. This type of differential has the same parts as an open differential, but adds an electric, pneumatic or hydraulic mechanism to lock the two output pinions together. This mechanism is usually activated manually by switch, and when activated, both wheels will spin at the same speed. If one wheel ends up off the ground, the other wheel won't know or care. Both wheels will continue to spin at the same speed as if nothing had changed. The detriot locker is about the best you can buy for this appication.
Spool
A Spool is considered to be a race only item. As you can see, it eliminates any kind of little gears and devices that could cause a rearend to break. The only real job it does is hold the ring gear in and tie the two axles together. For a drag car, this is the best item you can have as it will almost never break. For a daily driver, however, you will experience a lot of driveability issues such as having trouble backing, turning, parking and anything else that is not “straight-line” only.