USA Standard Pinion installation Kit For 99-08 GM 8.6in

Regearing a 1999-2008 Silverado or Sierra 1500 for bigger tires, or tracking down a whine that starts on light throttle and fades on coast? On the GM 8.6 in. 10-bolt both jobs come down to the pinion. USA Standard ZPKGM8.6-A is the pinion installation kit for that axle, which the maker describes simply as the 99-08 GM 8.6 pinion bearing and seal kit. It is meant for the common situation where the carrier bearings are still smooth and only the pinion side needs new parts, so you are not paying for a full master kit you will only use half of.

What the pinion bearings do in a GM 8.6

The 8.6 (ring gear 8.625 in.) is a C-clip, semi-float axle. The pinion rides on an inner and an outer tapered roller bearing pressed into the nose of the housing, with a crush sleeve between them. Tightening the pinion nut collapses the sleeve until the bearings carry the right preload. A shim under the inner bearing cone sets pinion depth, which controls where the teeth contact the ring gear. Those two bearings take all the thrust from the gear mesh, so when they wear the pinion starts to move under load, the pattern walks toward the edge of the teeth, and the axle sings. Yukon's own version of this kit, the PK GM8.6-A, is pitched the same way: gear installs on lower-mileage axles where the carrier bearings and races can be reused.

Symptoms tied to the pinion side

• Whine on light acceleration that changes or goes quiet when you lift, typical of pinion bearing or gear contact problems
• A clunk taking up slack when you go from coast back onto the throttle
• Up-and-down or in-and-out play at the pinion yoke with the driveshaft off
• Gear oil seeping from the pinion seal onto the yoke and the crossmember
• New gears planned, since a ring and pinion should never go in on the old pinion bearings

How to confirm before you buy

Our pinion bearing noise guide walks through the drive-versus-coast test. With the rear up and the driveshaft off, turn the yoke by hand: notchy rotation or play means the pinion bearings are done. Then check the carrier side. If the carrier bearings are also rough, buy the ZK GM8.6 master overhaul kit instead, because it covers both. If you are regearing, our GM 8.5 and 8.6 ring and pinion guide covers ratio and kit choices, and the Yukon 3.73 gear set is a common pick.

Fitment

This kit is listed for the 1999-2008 GM 8.6 in. rear only. GM changed the pinion bearings on the 8.6 for 2009, which is why 2009-and-later trucks use different kits such as the Yukon YK GM8.6-B. It is also not for the 8.5 in. 10-bolt it replaced, or the 8.6 IRS axle in the 2010-up Camaro, which has its own specs. Because 1999 and 2000 were changeover years between the drum-brake 8.5 and the disc-brake 8.6, check your rear brakes and the axle code on the RPO label rather than going by model year. If in doubt, send us your year and VIN. More kits are in our rebuild kits section.

Install notes

• Mark the yoke to the pinion and count turns on the nut before you start, so you know the old preload if you are only replacing the seal
• Drive the new races in fully with a race driver set; a race that is not seated will lose preload in a few hundred miles
• Final assembly always takes a new crush sleeve and pinion nut; a sleeve that has been crushed once cannot be reused
• Revolution's GM 8.5-8.6 numbers: 14-19 in-lb pinion preload with new bearings, .006-.010 in. backlash on five-cut gears, 65 ft-lb ring gear bolts, 60 ft-lb caps
• Tighten the nut in small steps and check preload each time; going past spec means starting over with another sleeve
• Refill with 75W-90 gear oil, plus friction modifier if the truck has the factory locker or a limited slip

Read our break-in procedure before towing on fresh gears.

Does ZPKGM8.6-A fit my 2010 Silverado?

No. The kit is for 1999-2008 GM 8.6 rears. GM changed the 8.6 pinion bearings for 2009, so 2009-up trucks need a different kit.

What is the difference between a pinion kit and a master overhaul kit?

A pinion kit covers the pinion side only, bearings, races and seal. A master overhaul kit adds carrier bearings, races and setup hardware. Choose the pinion kit when the carrier bearings are still smooth.

How do I tell an 8.6 from an 8.5?

On 1999-2008 GM light trucks the 8.6 has rear disc brakes and the 8.5 has drums. The axle RPO code on the glovebox label confirms it.

Can I reuse the crush sleeve and pinion nut?

No. The crush sleeve deforms permanently when the nut is torqued, and the nut should be replaced. Plan on a new sleeve and nut for final assembly.

What pinion preload should I set?

Revolution lists 14-19 in-lb for new bearings on the GM 8.5 and 8.6. Measure with an inch-pound torque wrench on the pinion nut with the carrier out.