Frequently Asked Questions

Find answers to the most asked questions about your purchase, order or shipping

The carrier, or carrier case, is the unit which the ring gear bolts to and axles slide into. The carrier case transfers power from the ring gear to the axles.

This is a hardened shaft which installs into the case and keeps the spiders securely in place. In semi-float applications, it also prevents the axles from sliding inward into the carrier case.

A limited slip differential is a type of carrier case where the spider gears are preloaded and prevented from turning easily via a friction surface. Once enough power has been applied to the spiders, which is called a breakaway point, the spiders can turn. The preload and friction can sometimes cause noise or “chatter” when negotiating a turn.

Pinion preload is the amount of resistance or “drag” measured when attempting to turn the pinion without the carrier installed.

The ring gear bolts to the carrier and is driven by the pinion gear.


The spider gears are a set of four to six gears which install into the carrier. The rotation of the spider gears allows one axle to spin faster or slower than the other.

Yes. The carrier bearing caps are bored at the factory and are side specific. Mixing up the carrier bearing caps can be a major mistake in rebuilding a differential, especially if it is a design which uses side adjusters. A good practice is to take a punch and mark one of the carrier bearing caps along with the side of the housing it belongs to in order to prevent mistakes during reassembly.
No. Many people think that shim kits are simply an assortment of shims of different thicknesses. The reality is that shim kits take a lot of time, research and quality control to get right. Many of our shim kits are designed by our in-house engineering and design team, ensuring you’re getting the highest quality components available. We review all shim thicknesses and quantities to determine what is best for each application, verify that the correct steel is being used, and verify that the heat-treating process has been done properly. The end result is a kit that is not only complete, but won’t compress or warp after installation. We stock more than 50 shim kits for a variety of applications, including our line of “Super Shims”. Super Shims are an interlocking carrier shim system that allows you to drive each side in as one complete unit. Standard carrier shim kits are difficult to install and easy to damage. We carry Super Shim kits for more than 15 applications.

The pattern refers to how the ring gear and pinion gears mesh. There is a process used when reassembling a differential that optimizes ring gear and pinion tooth contact. The procedure involves changing the pinion position via shims in the carrier and repositioning the carrier. Dialing in the tolerance between the gears will ensure a smooth-running, long-lasting differential.

For more info on reading gear tooth patterns, check out this video from our Resource Center.

Reading Gear Teeth

It is nearly impossible to measure the preload on a carrier because it is in contact with the pinion at the time of assembly and therefore is receiving resistance from it as well. A carrier should have to be loaded in with some resistance, such as a few hits from a dead blow hammer. It should not simply load in by hand, and it should not take a huge amount of force to put into place.

When traveling in a straight line where wheel speeds are identical on both sides, all LSDs continuously provide equal traction to both tires. The difference between LSD types has to do with how this occurs and what happens when additional traction is needed.

In a clutch-type unit, the spring array applies pressure to the side gears which puts pressure on the clutch packs in the outer part of the carrier. Both axles get equal pressure and both tires get equal traction. When a tire starts slipping, the clutch packs are engaged with different resistance. The clutches work to maintain synchronization between the tires, transferring more torque to the tire that has the best grip while reducing torque transfer to the tire that has less grip.

A gear-type LSD has no frictional surfaces to initiate torque transfer. It uses floating helical-cut worm gears that operate in pockets and mesh together. Under normal driving conditions this type of LSD acts like an open diff. When acceleration or wheel slippage occurs, axial and radial thrust is applied to the helical gear pinions in their pockets. Under these loads, more torque is transferred to the tire with the best traction in a progressive manner as torque is withheld from the tire that is slipping.

Whirring noise only while decelerating at any or all speeds is most likely caused by bad pinion bearings or loose pinion bearing preload, and almost never by bad ring and pinion gears.

A howl or whine during acceleration over a small or large speed range is usually caused by worn ring and pinion gears or improper gear set up.

Rumbling or whirring at speeds over about 20 mph can be caused by worn carrier bearings. The noise may change while turning.

Regular clunking every few feet may indicate broken ring or pinion gears.

Banging or clunking only on corners can be caused by broken spider gears, lack of sufficient positraction lubrication, or worn positraction clutches.

Rumble while turning may indicate bad wheel bearings.

A steady vibration that increases with the vehicle’s speed can be caused by worn u-joints or an out of balance driveshaft.

Clunking only when starting to move or getting on and off the gas might be loose yokes, bad u-joints or worn transfer case or transmission parts.

When a differential is traveling in a straight line, the spider gears remain motionless in the carrier. It is not until one tire turns faster or slower than the other that the spider gears rotate on the cross pin shaft. This most commonly happens when turning a corner. However, other situations cause the spider gears to spin much more rapidly, such as getting stuck in the mud or snow. When this happens, the spider gears can rotate on the cross pin shaft so quickly that it slings all the differential oil away from it, giving way to metal-on-metal wear. This causes the cross pin shaft and the gear to get so hot that they melt each other, sometimes to the point where they weld themselves together. Damage such as this can not only destroy the spider gear set, but compromise the carrier and ring and pinion set.

Size, as it relates to strength and ease of installation. The smaller Spartan Locker, also known as a lunchbox locker or an insert-type unit, is easier to install because it replaces the spider gears. Since the Spartan Locker is installed in the carrier it relies on said carrier for strength. The Grizzly Locker is bigger and significantly stronger. It replaces the entire carrier assembly and has more clamping force, forged internals, and a forged 8620 low-nickel alloy steel case that is much more robust than the OE carrier it replaces.

Gain more insight into lockers by checking out our “Installing a Spartan Locker,” “Unboxing a Spartan Locker,” and “Yukon Grizzly Locker” videos.

Installing a Spartan Locker

Unboxing a Spartan Locker

Yukon Grizzly Locker

The term “thick gears” refers to a ring gear that is thicker than stock to maintain proper meshing in a carrier that is being upgraded with a numerically higher gear ratio. When increasing gear ratio, a smaller diameter pinion gear is employed and the thicker ring gear makes up the difference by moving the gear teeth ‘higher’ so the two gears mesh properly.

Get more info on Yukon ring and pinion gears by watching our “Unboxing Yukon Ring and Pinions” video.

Unboxing Yukon Ring and Pinions

It is the measurement from the base of the housing to the gear teeth. This mounting surface within the housing changes to accommodate the smaller pinion gears that are used when swapping to numerically higher gear ratios. A taller deck height maintains proper contact between the ring and pinion gear teeth by moving the ring gear farther ‘up’ in the housing.

A clunking sound that only occurs while turning is a result of broken or damaged spider gears. Spider gears do not move at all while traveling in a straight line so they’ll only squeal when turning. If this is the case then the spider gears will need to be replaced and possibly the carrier as well. Be sure to inspect the ring and pinion to confirm  floating debris did not damage it as well.

Spider gears are also known as satellite gears, they rotate around the side gears in the differential carrier. Side gears may also be referred to as axle gears or planetary gears. The spider gears are the ones with the cross-pin shaft going through them. This array of spider and side gears take the rotational energy from the driveshaft and help redirect it outwards to the axles and on to the wheels. They also play a key role in allowing the wheels to rotate at different speeds when the vehicle is turning.

For a more in-depth look, view this installation video from our Resource Center.

Spider Gears Video

These kits are for shops and builders who have shims on-hand and are looking to save money over a Master Overhaul Kit. They include carrier bearings and races, pinion bearings and races, a pinion seal, marking compound, and a brush.

Set-up bearings are bearings which have had their inner diameters machined so they slide on and off a pinion shaft or carrier journal. The advantage to using set-up bearings is that you can quickly install or remove them with different amounts of shims to check both pinion depth and backlash without having to worry about the nice, new bearings you just purchased. Once the correct amount of shim(s) have been found, you simply remove the set-up bearing(s) and install the new bearings with the correct shim.
Do NOT use bearing grease on your carrier bearings or pinion bearings when setting up your differential. This could cause premature failure from the oil not having the ability to lurbicate the bearings properly. Use clean gear oil only to pre-lubricate your bearings during the install.