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Tech and Diff FAQ

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Technical Help

Looking for information on parts and their applications?

Rwkhaussupply has gathered technical information to better serve you. Here you’ll find many articles ranging from adjusting positractions to choosing a shop to take your vehicle.

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General Information


Are all shim kits created equal?
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 & quality control to get right. Many of our shim kits are designed by our in-house engineering & 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 over 50 shim kits for a variety of applications, including our line of “Super Shims”. Super shims are an interlocking carrier shim kit that allows you to drive each side in as on complete unit. Standard carrier shim kits are difficult to install and easy to damage. We carry super shim kits for over 15 applications.

Are carrier bearing caps side specific?
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.

Can a ring and pinion from two different sets be used together?
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.

Can I re-use a crush sleeve?
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.

Can Synthetic Oil be used in a Dura Grip?
Yukon recommends the use of high grade GL-5 gear oil and Yukon LSD (Limited Slip Differential) additive for long life and smooth operation. Part number OILADD. The use of synthetic oil is allowed but may result in aggressive or noisy operation.

Do I have a traction device such as a positraction or locker in my vehicle?
Put the transmission in neutral and jack up both tires. Turn one tire. If the other tire spins the opposite direction then you have an open differential, and if it spins the same direction then you do have a traction device.

Do I need a positraction or a locker?
A limited slip or positraction differential typically uses some form of clutches that bind up the differential, providing traction to the both tires. The clutches will slip to some extent to allow tires to turn at different speeds on corners. Some limited slip differentials are more aggressive than others, and some can be set up or "pre-loaded" more or less aggressively. Limited slip units require a special gear oil additive and may chatter when turning. Clutch packs may also wear with time and require replacement.

Do I need to change my gear ratio?
Here's 4 Reasons To Change Your Gear Ratio.

If you have larger than stock tires on your vehicle, the benefits of gearing CANNOT BE MATCHED BY ANY OTHER MODIFICATION TO THE VEHICLE!

By regearing it is guaranteed that:

Even a simple change from a 31" diameter tire to a 33" diameter tire will affect the amount of available torque by 10%.

Modern day transmissions cost $600 or more to perform a basic overhaul. Driving with even a 10% larger tire will result in the transmission being under the same load as always being driven on an incline. The transmission may not suddenly fail, but the life will definitely be reduced by thousands of miles.

RPM alone does not affect fuel mileage. An undergeared vehicle (as the result of oversized tires) will result in a substantial loss of fuel mileage. Also, just as with the transmission, your engine life will greatly be reduced.

With kits in the $100+ range to calibrate speedometers after tire swaps, it seems pretty important to have an accurate speedometer, which can also be fixed with a simple gear change.

Don't put a bandage on a serious problem. By installing the proper gear ratio, easily determined with our gear calculators, you can save thousands of dollars and days of vehicle downtime, plus have a little fun to boot.

How do I measure the preload on my carrier bearings?
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.

How hard do I need to tighten my side adjusters?
Most people are reluctant to really crank down on the side adjusters in their differential. Attaining a good preload through the side adjusters can be critical in protecting your differential from the high torque loads that cause ring gear deflection. It is not uncommon to torque side adjusters to 150-200 ft/lbs when setting up a differential.

How much torque is needed to crush a crush sleeve?
On a crush sleeve design differential it usually takes between three hundred (300) and four hundred (400) foot pounds of torque to crush the crush sleeve. Over the years I have used huge breaker bars and/or very strong air operated impact wrenches to crush the crush sleeve.

How often should I change my differential oil?
For a normal, daily driven, vehicles we advise that you change the differential oil every 50,000 miles. For vehicles that are hard worked, such as trucks that do a lot of heavy towing, we advise that you change the differential oil every 15,000 miles.

I can’t get a good drive pattern on my used gear. What’s wrong?
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 get worn 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.

Is driveline "slop" normal with a locker?
Yes. It is not uncommon to gain up to a third of a rotation of "slop" in your driveline after a locker has been installed. This is perfectly normal, and is all part of how the locker operates.

My cross-pin shaft is scored and the spider gears wore into it. What happened?
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 damage the spider gear set, but destroy the carrier and ring & pinion set.

Should I use bearing grease on bearings during install?
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.

What are set-up bearings?
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.

What gear ratio do I have?
Jack up one tire if you have an open diff, or both tires if you have a working posi or locking differential. Rotate the tire one full revolution for posis and lockers and 2 full revolutions for open diffs. Carefully count the number of full revolutions the driveshaft makes. This is your gear ratio. In other words, if the drive shaft turns 3 ¾ turns, you probably have a 3.73 gear ratio. Turning the tire for twice the number of full revolutions and dividing the drive shaft revolutions by two will give you a more accurate reading.

What gear ratio do I need?
Differential Gear Ratio determines the number of times the drive shaft (or pinion) will rotate for each turn of the wheels (or ring gear). So if you have a 3.73:1 gear ratio the drive shaft turns 3.73 times for every turn of the wheel.

Gear ratio is calculated by dividing the number of teeth on the ring gear by the number of teeth on the pinion gear. The higher the number, the lower the ratio: a 5.29 gear has a lower ratio than a 4.10 gear. With a lower gear ratio the drive shaft (and thus the engine) turns more for each revolution of the wheel, delivering more power and torque to the wheel for any given speed. Lower ratios are generally desirable when going off-road. Higher ratios are better for freeway driving since they run at lower RPM’s and offer better fuel economy.

Changing tire size affects the final drive ratio. Switching from a 30" tire to a 35" tire changes the final drive ratio by about 17%. This may drop the engine out of its' "power band" and result in poor performance and fuel economy. To restore performance you must change the gear ratio to compensate for the change in tire size. If you originally had 3.07 gears you need a ratio that is approximately 17% lower, such as 3.55. If you want to increase off road performance you might want a 4.10 or lower ratio.

What is a solid spacer?
A solid spacer replaces the crush sleeve in a differential. It is a solid piece of machined steel which is slightly shorter than a crush sleeve and comes with a variety of shims. The shims are stacked with the solid spacer to achieve different levels of preload on a pinion, the same way as a crush sleeve. The advantage of using a solid spacer & shim set up is that you don’t need to worry about over-tightening the pinion nut, as you do with a crush sleeve. Also, once the preload is set, you never need to worry about adjusting it or replacing anything, like if you have to replace a yoke. When setting preload, you add shims to decrease the amount of preload on the pinoin bearings, and remove shims to increase the amount of preload on the bearings.

What is that clunking sound I hear while turning?
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. If this is the case then the spiders will need to be replaced and possibly the carrier as well. Be sure to inspect the ring and pinion to be sure broken debris did not damage it as well.

What is the best marking compound to use when setting up a ring & pinion?
The best compound we have found for checking a pattern is a tan, “peanut butter” colored type. There have been other colors over the years, including a dark blue compound, however the dark color of the blue makes it difficult to get a clear view of the pattern against the dark color of the ring & pinion set. The tan color provides a good contrast of colors and is much easier to see.

What is the break-in proceedure for a new set of gears?
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. I recommend at least 500 miles before towing. I 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 I have seen many differentials damaged from being loaded before the gear set was broken in.
I also recommend changing the gear oil after the first 500 miles. This will remove any metal particles or phosphorus coating that has come from the new gear set.

What is this whirring noise?
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 I installed my gear set it was quiet, but it's getting loud with time. What happened?
It is most likely a result of the gear not being broken in properly or driven "too hard, too soon." When this happens, the gear oil breaks down and the resulting temperature inside the differential causes the face of the gear to wear away exposing the softer metal underneath. When this happens the gear will wear down more and more until the gear completely fails.