Yukon Gear Master Overhaul Kit For 99-08 GM 8.6in Diff

If the rear of your 1999-2008 Silverado 1500, Sierra 1500, Tahoe, Yukon or Suburban 1500 has started to howl at highway speed, growl louder as you go faster, or leave a ring of gear oil around the pinion yoke, the 10-bolt behind it is most likely the GM 8.6. The Yukon Gear and Axle YK GM8.6-A is the master overhaul kit for that first-generation 8.6: every bearing, race and setup part you need to rebuild the center section, whether you are reusing the factory gears or installing a new ratio.

What the master overhaul kit does in a 1999-2008 GM 8.6

The 8.6 is GM's half-ton truck version of the corporate 10-bolt, a C-clip, semi-float rear with an 8.625 in. ring gear (everyone rounds it to 8.6). It replaced the drum-brake 8.5 when GM moved its light trucks to rear disc brakes, and it runs 30-spline axles. Inside, the pinion rides on a pair of tapered roller bearings that are held under preload by a collapsible crush sleeve, and the carrier spins on two side bearings with shims behind them. Those shims set backlash and carrier preload; the pinion depth shim sets how deep the pinion teeth sit in the ring gear. When the bearings wear, preload goes away, the gears move out of their contact pattern and the axle starts to sing.

This kit contains Timken carrier bearings and races, Timken pinion bearings and races, a pinion seal, a complete shim kit, ring gear bolts, a pinion nut, a crush sleeve, thread locker, gear marking compound with a brush and a cover gasket. Axle seals and axle bearings are not part of the kit. Yukon also builds a separate YK GM8.6-B for 2009-and-newer trucks, because GM changed the pinion bearings that year.

Symptoms that point to the 8.6 center section

• Whine that comes in at a certain speed and changes between accelerating and coasting
• A rumble or growl that grows with road speed whether or not you are on the throttle
• Clunk when you shift into drive or get on and off the gas, from a loose pinion
• Wet pinion seal, often with oil slung onto the crossmember or the exhaust
• Glitter or chunks on the fill plug or in the oil when the cover comes off
• Noise that started after a regear that was never checked with marking compound

How to confirm it before you order

Hold a steady 50 mph, then lift off and coast. If the sound changes with throttle, the gears or bearings are the problem; if it changes when you weave the truck left and right, look at the wheel bearings first. With the rear on stands, rock the pinion yoke up and down. Any clunk or play means the pinion bearings have lost preload and a crush sleeve and bearing job is due. Measure backlash with a dial indicator and magnetic base before teardown so you have a baseline, and drain the oil through a clean pan to see what is in it.

Fitment

The YK GM8.6-A is listed for the 1999-2008 GM 8.6 in. rear. The quickest check is the brakes: the 8.6 has rear discs, and the 8.5 it replaced has drums. Because 1999 and 2000 were transition years, some early trucks still carried an 8.5, so look at the brakes, the axle tag and the RPO codes on the glovebox label, not just the model year. A 2009-and-newer truck takes the Yukon YK GM8.6-B 2009-up kit. If you prefer Koyo bearings at a lower price, the USA Standard 1999-2008 GM 8.6 master kit covers the same axle. Not sure which you have? Send us your year and VIN before it ships, or browse every axle kit on the rebuild kits page.

Install notes

• Paint a few ring gear teeth with the included compound and turn the pinion both ways before teardown. A photo of that pattern tells you whether the old pinion depth was right.
• Pull the C-clips by removing the cross shaft lock bolt and cross shaft, pushing each axle in and lifting the clip out.
• Keep the original carrier and pinion shims labeled; with the original gears they are your starting point.
• Use the new crush sleeve and creep up on pinion preload, checking turning torque every few degrees. If you overshoot, the sleeve has to be replaced, not backed off.
• Clean and dry the ring gear bolt threads, apply the thread locker and torque them in a cross pattern.
• If the gears are pitted, regear now. A GM 8.5/8.6 3.73 ring and pinion installs with this kit, and the front axle on a 4x4 must match the new ratio.
• Pinion yokes on the 8.6 use the later triple-lip seal; a truck that sees mud or rocks benefits from a Yukon nodular iron 8.6 cover.
• Refill with the gear oil grade in your owner's manual (75W-90 is typical) and add friction modifier if the axle has a G80 locker or posi.

Will this kit fit my 2010 Silverado 1500?

No. The YK GM8.6-A is for 1999-2008 GM 8.6 rears. GM changed the pinion bearings for 2009, so 2009 and later trucks need the YK GM8.6-B kit.

How do I tell an 8.6 from an 8.5 on my truck?

Look at the rear brakes. The 8.6 uses disc brakes and the 8.5 uses drums. 1999 and 2000 were transition years, so confirm with the axle tag or the RPO codes on the glovebox label.

Does the kit include axle bearings or axle seals?

No. It covers the center section: Timken carrier and pinion bearings and races, pinion seal, shims, ring gear bolts, pinion nut, crush sleeve, thread locker, marking compound and gasket. Buy axle bearings and seals separately if the outer ends are worn or leaking.

Can I reuse my original ring and pinion?

Yes, if the teeth are not chipped, pitted or blued. Reuse the original pinion depth shim as your starting point and verify the contact pattern with the included marking compound.

What gear oil goes back in?

Use the grade your owner's manual lists; 75W-90 is the common fill for these axles. Trucks with the factory G80 locker or a clutch-type posi should get a friction modifier if the manual calls for it.