Spools & Mini Spools:
For racing, serious off-road, or crazy hot-rodders, a spool is the ultimate traction differential. Actually, it can hardly be called a differential because it does not differentiate. Spools have several purposes in a differential. First, they lock both left and right axles solid together so that there can be no loss of power due to the unit allowing one wheel to spin faster than the other. Second, they usually support the ring gear much better than most other differentials. Last, they can be lighter than a differential, which saves rotating mass as well as un-sprung weight that the suspension has to contain. The main shortcoming of spools is the fact that the outside wheel has to turn faster when negotiating a turn if both wheels are to maintain traction. If the axles are locked together, one or both wheels have to slip in order for the outside wheel to travel farther than the inside wheel. This can cause the rear of the vehicle to spin out, fish-tale, or can cause a lot of noise that sounds like positraction clutch chatter as the axles twist and release. Sometimes these effects are not all that bad, and they are less severe when 35-spline or larger axles are used. For those people on a budget, there are mini-spools available for many rearend designs. A mini-spool fits inside the standard open carrier, replacing the spider gears, and locking the left and right axle shafts together just like a spool does. A mini spool drives exactly like a full spool does, but they are not as strong as a full spool and do not add any extra support to the ring gear like a spool does.
Auburn Gear (AG)
The Auburn Gear limited slip uses a cone style clutch that wears directly against the carrier case and provides the friction force to make the unit work. This design is not rebuildable. Once the cone clutch or case wears out, the entire unit must be replaced. Even with this shortcoming, this design works well for occasional use where extra traction is needed. They have good impact strength in passenger cars and trucks up to 1 ton. They will hold up well to high horse power, but will not last long if there is a lot of tire spinning.
Detroit Locker (DET)
Heavy duty. Probably the most durable design available, the king of traction differentials. Usually causes banging and clunking, but gives 100% lock-up whenever traction is needed. Unlocks when negotiating a turn so that the outer wheel can turn faster than the ring gear is turning and the inside wheel are turning. Does not need any interaction from the driver. New Sof-Locker design has damping device to reduce banging and clunking. Includes carrier case that is stronger than stock except in 2 applications where the original factory carrier case is used. Only the 10.5" 14 bolt truck and the Nissan V6 designs use the factory carrier case and these cases are both very strong.
Eaton (EAT)
Clutch type, similar to Trac-Lok in design, yet far stronger like a Power-Lok, and, more aggressive and better lock-up similar to the Power-Lok design. These units came as an original equipment option in 65-72 12T (12 bolt GM truck), 12P (12 bolt GM passenger), 8.2" GM pass, 63-79 Cast Iron Corvettes. The original OEM 12T case was very weak, but the new design replacement from Eaton is very strong. 4 preload springs and 2 steel preload spring plates. Latest design uses HD nodular iron case, forged side and pinion gears, no-chatter, race-bred, carbon fiber clutches for extreme strength and longevity. Old design, all steel clutches which are still available in 18 or 22 clutch designs for those who need more lock-up and are not bothered by clutch chatter. For even more lockup customization, there are also 4 levels of spring pressure available (3 from Eaton and a fourth from GM) that can be used to vary the clutch preload from 200 lbs. to 800 lbs. Originally used in mid sixties GM muscle cars and trucks. This unit is now available for Ford applications and soon will be available for Dana Spicer, AMC, and Chrysler applications. They have a high tolerance for abuse in high horsepower vehicles. Recommended for everyday driving and severe off-road use
Trac-Lok (T/L)
Built by Dana Spicer for use in Spicer rearends, AMC rearends, and 1998 & older 10.25" Ford rearends. The old design built up until about 1989 was weak. The 1990 and newer design is fairly strong and even rivals the Power-Lok for impact durability, but the clutches do not provide as much lock-up force and tend to wear out in about 50,000 miles if used in the rear. Works better in the front of vehicles because it's not aggressive. The main selling points for this design are the fact that clutch chatter is almost non-existent, and it is very inexpensive. These two points make it a great unit for many applications and a very good value for the money. This unit makes a great front limited slip and works well for those who need a little extra traction but cannot tolerate clutch chatter. The Trac-Lok came factory installed in many models such as D28, D44, D60, AMC 20, AMC35, 10.25" Ford. The problem with this unit is that it is not very aggressive and power transfer is minimal. Also, 1988 and earlier units tend to break fairly easily. (1piece case, 2 pinion gears, and 2 tab clutches). (factory )
There are really a lot of types and depending on your application that is how you should choose what you need.