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Frequently Asked Questions

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

A device that disconnect one front axle shaft from the differential via a splined, sliding collar. This system only works with open differentials and it still allows the differential side and spider gears in the differential to rotate.

Numerically high gear ratios. Generally speaking, ratios from 4.10:1 to about 6.13:1 are considered low gears. Lower than 4.88:1 is “super” low while ratios from 3.54:1 to 4.10:1 are regarded as moderately low.


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.

The input drive for the differential, a shaft with a small gear attached. The “spider” gears in an open differential are also called pinions.

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.

The side gear fits into the housing and has splines on the inside which accepts the axle splines. Side gears are part of the spider gear set.

All new gear sets require a break-in period to prevent damage from overheating. After driving the first 15 or 20 miles it is best to let the differential cool before proceeding. We recommend at least 500 miles before towing. We also recommend towing for very short distances (less than 15 miles) and letting the differential cool before continuing during the first 45 towing miles. This may seem unnecessary but we have seen many differentials damaged from being loaded before the gear set was broken in.
Changing the gear oil after the first 500 miles is also recommend. This will remove any metal particles or phosphorus coating that has come from the new gear set.

Get more info in these blog articles Proper Break In Process – Keeping Gears Cool During Break-In –  12 Tech Tips For Proper Differential Assembly & Setup


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

Transfer cases use a combination of Drive, Housing, and Shift Types.

Drive types:

Gear driven transfer cases use a set of gears to send power to the front and rear axle. While gear driven transfer cases are more durable, they are also louder and less practical for smaller vehicles because of their weight.

Chain driven transfer cases use a chain in place of a gear set. Though most chain driven cases only drive one axle, there are case systems designed to drive both axles with a chain. Chains are lighter and quieter, but weaker than gear sets.

Housing types:

Married transfer case housings are bolted to the transmission, often between the output shaft and the main driveshaft. Some married transfer cases share their housing with the transmission.

Independent housings are installed separately from the transmission casing and are connected to the transmission output shaft with another driveshaft.

Shift types:

Manual Shift On-the-Fly (MSOF) transfer cases are controlled with a lever on the driver’s side floor of most vehicles. These transfer cases have two automatic sealed front axle hubs or two manual front axle hub selectors. High 4WD settings can be engaged at low speeds, but low 4WD settings must be engaged when the vehicle is stationary and the transmission is in neutral.

Electronic Shift On-the-Fly (ESOF) transfer cases have a dash-mounted selector, usually a switch or set of buttons. These cases have sealed automatic locking front axle hubs and a transfer case motor. High and low 4WD is engaged in the same ways as a MSOF transfer case.

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.

Variables to consider include tire size (especially if it’s changing), transmission ratio, rpm at cruising speed, the stock gear ratio, and the intended usage of the vehicle. The tradeoff here is off-the-line acceleration versus freeway-speed performance.

Re-gearing serves two purposes. It can re-gain lost drivability in daily driven vehicles that have bigger tires installed or custom tailor performance for a dedicated off-roader that doesn’t put as much emphasis on daily driving.

If you’re adding big tires, technically you’re already re-gearing your ride because the increase in tire circumference changes the final drive ratio. Think about it this way… if you’re running a 3.73 gear, the pinion gear rotates 3.73 times to turn the ring gear one full rotation. On the road a bigger tire will take more rotations to get up to speed (slower) but require a lower engine rpm to maintain a highway speed. In some cases, bigger tires can create profoundly adverse driving characteristics and a reduction in fuel efficiency.

To figure out what your rig is doing and how to pick the right ratio you need to know your gear ratio and tire height in stock trim. These factors can be used to determine your engine rpm at a given vehicle speed. Our homepage has easy-to-use calculators that compute gear ratio and tire height. Then you take those numbers and feed them into our RPM calculator.

Use your stock set-up as a baseline to see what your stock vehicle speed to engine speed relationship is. If your rig is a daily driver you’ll want to gauge performance at freeway speeds. If you’re dialing in a dedicated off-roader, freeway speed performance will be less critical so you may want to evaluate slower vehicle speeds. Once your baseline is established, enter your new tire diameter and adjust the gear ratio to best match the stock numbers for daily drivers or the desired performance of a dedicated off-roader.

Check out our calculators here.

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

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.

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

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.

No. Once the crush sleeve’s tension between the bearings is released it cannot hold the proper tension again. This is also true if a crush sleeve is over-crushed during installation. It must be discarded and replaced with a new one.
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.
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 testing your pattern on a used gear, it is often difficult or impossible to get a good pattern on the drive side of the gear. The reason for this is that through use the drive sides of the gears wear and won’t show you the pattern clearly. The solution is to check the pattern based on the coast side of the gear. In standard rotation front differentials, you will still want to check the drive side of the gear since that is the side which gets the least amount of wear in those applications.

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, sometimes called a mechanical locker or automatic 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

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.

It’s all about math… and counting teeth. Simply count the teeth on the ring gear and divide that number by the number of teeth on the pinion gear. Be aware that you may have to round off the number. (45 divided by 12 = 3.75… rounded to 3.73). The ratio itself refers to how many times the pinion gear rotates to turn the ring gear one full rotation.

Some are, some aren’t.

Clutch-type LSDs, like our Dura Grip, can be rebuilt. Rebuilding involves replacing the clutches in the unit. The clutches can be replaced to bring the unit back to its original performance level, or non-stock clutches with different friction characteristics and springs with custom compression rates can be used to fine tune the Dura Grip’s performance to better match the style of driving/racing you are doing.

Gear-type LSDs, like our Spartan Helical, do not require rebuilding because there are no clutches to replace, there is nothing to rebuild. The unit’s internal worm gears should last the life of your vehicle.

We predominantly use five metal types; 4320, 4340, 8620, 9310, and 1541H.

4300-series is a nickel-chromium-molybdenum alloy, i.e. chromoly, that’s low in carbon content. 4320 is used for the internals in our line of Yukon Dura Grip LSDs. We use 4340 in the manufacturing of forged gears, pinion gears, high-performance axles, Super Joints, and more. 8620 is a low-nickel alloy steel generally used in the manufacture of forged camshafts, crankshafts, and fasteners. We use it in gears and cases. 9310 is an alloy steel with more nickel and chromium than 8620. 9310 can better endure high shock loads without failing and we use it in Spartan Lockers. 1541H is a high-grade carbon steel used in our replacement axles and u-joints, and similar products. A caveat here, heat-treating plays a definitive role in a given alloy’s hardness and other properties that impact their performance in automotive drivetrain applications. We use advanced heat-treating techniques to fine tune our alloys to their intended usage.

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.

We do all the thinking. Each kit contains all the parts needed to complete the job from start to finish so you know you’re getting all the right stuff the first time. The kits include a ring and pinion and all the bearings, seals, and small parts in one simple part number. Some kits are configured to address one axle, some cover both, and some include a Dura Grip limited-slip differential. A Yukon Pro Kit features a premium Yukon Gear & Axle gear set and uprated hardware to meet the demands of wheeling, off-road racing, track racing, street driving, and performance diesel. USA Quick Kits are affordable, general repair options when stock performance and reliability are the prime concerns.

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.
Normally the flow of power goes from the transmission to the rear wheels through the driveshaft. However, when you shift into 4WD that power has to be split between the front  and rear wheels. The transfer case makes this split happen. When you shift into 4WD, gears are engaged to power a chain drive that runs from a gear driving the rear driveshaft to power another set of gears behind the front driveshaft. Once engaged, this driveshaft delivers power to the front differential and out to the front wheels.
No. Gear sets are lapped at the factory and are a matched set. Attempting to run two different gears together will result in gear noise and eventual failure.
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.

The "GL-5" designation identifies how much Sulphur-based friction modifier is present in the oil. This chemical modifier helps the oil function under extreme pressure… like in an LSD. Note: Because of its Sulfur content GL-5 oil is meant to be used on hypoid gears in differentials only; it is too corrosive to be used in transmissions, which require a milder GL-4 formulation.

Pinion bearing preload is related to the amount of force the pinion nut exerts on the pinion and its bearings. Axle builders generally measure the pinion’s preload by rotating the pinion gear by its nut with a pound/inch-graduated torque wrench. Crush sleeves or shims are generally used to set pinion preload. The proper torque ratings for new bearings can be found in the front of the installation manual on the Set Up Specifications page or by way of the chart below. Note: Measurements are for the use of new (not used) bearings.


Gearheads have their own vernacular so knowing the lingo will help you communicate with your mechanic. We’re talking about gear ratio. Tall gears produce a lower numeric ratio i.e. 3.08, 3.73 (or lower), while short gears or deep gears refer to higher numeric ratios i.e. 4.88, 5.29 (or higher).

Numerically higher gear ratios produce more torque, are quicker off the line, and deliver a lower top speed. Conversely, lower numeric gear ratios produce less torque, are slower at launch, and deliver a higher top speed. For more on how to pick the right ratio, check out this video.