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Spools are all about getting full lockup on a budget… 100% lockup 100% of the time. There are two types of spools: full spools and mini spools. Each attains the same objective, ensuring both drive wheels on a given axle receive full torque and rotate at the same speed all the time. They create a solid axle.
The Spool Compromise
As with any drastic, all-in type of modification there are compromises along the way. The spool is no different. Since the axles are locked there is no 
allowance for situations where the tires need to spin at a different speed… i.e. when the vehicle turns a corner. When this happens the tires chirp, sometimes aggressively, as they struggle to complete the turn. The rubber is the weak link. It’s what gives to allow the vehicle to maneuver. In doing so tires absorb a lot of abuse in the form of significant wear. One should also remember even when not pushed to the level of chirping, any imbalance in wheel speed is scrubbed off by the tires resulting in tire wear. Simply put, spools chew up tires.
Another compromise is how the binding within the differential also produces undue stress on the axles themselves. In the long term, axles can bent out of shape because of the torsional stress they are subjected to on the street.
Changing Driving Dynamics
There is a cause-and-effect scenario going on here. In most cases, running a spool will compromise the turning radius of the vehicle. Further, a spooled driveline can be unforgiving driving on wet/snowy roads as it lacks the finesse to handle conditions that call for the management of different wheel speeds to ensure vehicle stability and control.
You can roam the online forums and the street-worthiness of a spool-equipped vehicle is a long-raging debate. Due to their unwieldy nature, we recommend spools as an outstanding choice for dedicated off-road and drag racing vehicles only.
Full Spool
A full spool replaces the carrier, spider, and sides gears. The unit consists of a snout and a ring flange. The axles are installed in the snout, which is splined to accept the axle shafts. The spool’s ring flange bolts onto the ring gear. So, the ring and pinion do.jpg)
their job, redirecting torque 90 degrees from the driveshaft to the wheels but the housing has lost its ability to differentiate wheel speeds between the wheels. Yukon and USA Standard Gear spools are made from high-quality 8620 steel and heat-treated for additional strength so your differential is ready for extreme action in the name of ultimate traction.
Mini Spool
A mini spool is less expensive than a full spool. Since it swaps in place of the spider gears and side gears installation is easier, faster, and cheaper than a full spool. Though Yukon and USA Standard Gear mini spools are constructed from heat-treated 8620 alloy steel they are not as stout as full spools because minis rely on the factory carrier for strength.
Cost Versus Reward
We see our spools as a safer option for those who are considering welding their gears together to get the same solid-axle traction. The big problem is that welding can be done poorly and fail. Either by weak welds or too much heat which compromises the grain structure of the steel causing the gears to become brittle at the weld point and eventually break. When welded diffs let go they can take other components out… which negates any cost savings of welding. In our eyes, spools are only for dedicated off-road and drag racing vehicles. If the vehicle will see the street we urge customers to consider stepping up to a locker or limited slip differential.
Cost Versus Capability
You can opt for a Spartan Locker, a helical positraction LSD, or a locker. While each of these products represent a step up in streetability, they also embody a rise in cost. A full spool runs around $320 to $375. A Spartan Locker checks in at $400 to $500, provides full lockup, and although it may click occasionally it is far more civilized than a spool. Our helical positraction limited slip differentials start at $600, seamlessly enhance traction on the street, but do not provide full lockup. Yukon’s Grizzly Locker, an automatic locker / selectable locker, starts at about $780 and delivers 100% lockup and the ability to automatically unlock when needed.
Of course, pricing is application dependent, but for very little extra investment you can get a Spartan Locker or helical LSD. In many cases you will save money in the long run by not shredding and buying new tires on the regular. If you run expensive big tires like 35-, 37-, or 40-inchers the savings could be substantial.
Spools do what they’re intended to do and we build ours with quality materials and top-notch craftsmanship. But these products are narrowly focused on dedicated purpose-built vehicles that aren’t expected to be driven on the street or even make a 90-degree turn. Seriously consider your vehicle’s usage expectations and consider more than the initial cost. Look down the road, moving up to a more versatile, driver-friendly traction device can be the best call for your wallet and your nerves.
