Yukon Gear Master Overhaul Kit For GM 8.5in Rear Diff

A Chevy C1500 or K1500 that howls at 55 mph, a Tahoe with a wet pinion seal, or a Monte Carlo, Cutlass or Camaro rear that started to growl on decel all point to the same box of parts. The Yukon Gear and Axle YK GM8.5 is the master overhaul kit for the standard GM 8.5 inch 10-bolt rear: 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 the cover gasket. It is built for the factory open or GM posi carrier, not the large-journal aftermarket units.

What the master overhaul kit does in a GM 8.5 10-bolt

The 8.5 is GM's C-clip rear with a 10-bolt cover. The pinion turns on a large head bearing next to the gear and a smaller tail bearing near the yoke, held to a set rotating preload by a collapsible crush sleeve and the pinion nut. A shim under the head bearing sets pinion depth. The carrier rides on two side bearings, and the shims behind them set carrier preload and backlash. Yukon's catalog lists this kit with LM501349 and LM501314 Timken carrier bearings, which fit carriers with 1.625 inch bearing journals. When any of the four bearings wears, the pinion moves under load, the tooth pattern walks off center and the gears start to sing. This kit replaces every bearing and the parts that wear out with them, so you can set the axle up from scratch with your current gears or a new ring and pinion.

Symptoms that point to a rear overhaul

• Whine that climbs with road speed and changes between throttle and coast
• A steady rumble at highway speed that does not change when you swerve (wheel bearings usually do)
• Clunk on takeoff or in-and-out play at the yoke from a loose pinion nut or tired crush sleeve
• Gear oil on the yoke, driveshaft or the nose of the housing from a leaking pinion seal
• Glitter or bearing flakes in the oil when the cover comes off

How to confirm before you buy

Road test at the speed where the noise is worst and note whether it shows on acceleration, deceleration or both; our whine on acceleration versus deceleration guide explains what each pattern means. With the rear in the air, rock the yoke for play and spin the pinion by hand to feel for roughness. Pull the cover, check the oil, then paint the ring gear and read the pattern. Chipped or pitted teeth mean new gears, such as the USA Standard GM 8.5 3.73 ring and pinion. Then look at the carrier. If it is a Yukon Dura Grip, Eaton Posi, TrueTrac, Detroit or another large-journal unit, you need the YK GM8.5-HD kit instead.

Fitment

Yukon's fitment table for the YK GM8.5 covers a long run of GM rear-drive vehicles with the 8.5 inch rear, including 1970-1981 Camaro and Firebird, 1971-1976 El Camino, 1973-1978 Monte Carlo, 1975-1996 Caprice, 1994-1996 Impala, 1970-1977 Cutlass, 1979-1986 C10 and K10, 1988-1999 C1500 and K1500, 1995-1998 Tahoe, 1992-2000 Yukon, 1996-2003 Express and Savana 1500, and 1994-2000 S10 and Sonoma. GM used more than one 10-bolt in many of these years, so confirm the axle before ordering: the 8.5 has a 10-bolt cover and a 5/16 inch pinion shaft lock bolt, and the axle code on the tube or the RPO code in the glovebox tells you for sure. The 8.6 inch rear in later trucks uses a different master kit. If you are not sure, send us the year and VIN, or browse the differential rebuild kits.

Install notes

• Mark the bearing caps, measure the old backlash and record the pinion rotating torque before teardown.
• Yukon's setup chart for the GM 8.5 and 8.6 lists 14-19 in-lb pinion preload with new bearings, 6-11 thousandths backlash on 5-cut gears, 65 ft-lb on the ring gear bolts and 60 ft-lb on the cap bolts.
• Tighten the pinion nut in small steps and check preload each time. If you overshoot, the crush sleeve has to be replaced; the GM 8.5 crush sleeve eliminator is an option for a hard-used rear.
• Use the included thread locker on the ring gear bolts and the marking compound to confirm the pattern before final assembly.
• Fill with the GL-5 gear oil your manual calls for and add friction modifier for a clutch-type posi; see our friction modifier guide.
• If you are reusing the cover, a Yukon Hardcore 8.5 cover adds protection for trucks that see rocks.

What comes in the Yukon YK GM8.5 kit?

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 the cover gasket.

Will it fit my aftermarket posi or locker?

Only if the carrier uses the standard 1.625 inch bearing journals. Most aftermarket units such as Dura Grip, Eaton Posi, TrueTrac and Detroit use larger journals and need the YK GM8.5-HD kit.

Can I reuse my ring and pinion with this kit?

Yes, if the teeth are not chipped or pitted. The kit has everything to set the original gears back up. If the gears are damaged, install a new ring and pinion at the same time.

How do I know I have an 8.5 and not an 8.2 or 8.6?

Check the axle code stamped on the right tube or the RPO sticker, and look at the cover and pinion shaft lock bolt. The 8.5 uses a 10-bolt cover and a 5/16 inch lock bolt. Send us your year and VIN if you are unsure.

What preload and torque specs do I use?

Yukon's chart for the GM 8.5 and 8.6 lists 14-19 in-lb pinion preload with new bearings, 6-11 thousandths backlash on 5-cut gears, 65 ft-lb ring gear bolts and 60 ft-lb cap bolts.

What gear oil should I use after the rebuild?

A GL-5 gear oil in the viscosity your owner's manual lists. Add limited-slip friction modifier if the rear has a clutch-type posi, and follow a break-in before towing.