Yukon Gear High Performance Gear Set For GM 8.5in & 8.6in in a 3.08 Ratio
A GM 10-bolt rear that howls at 60 mph, a Chevy or GMC half-ton that was swapped to a deeper ratio and now screams on the interstate, or a muscle car build with an overdrive transmission that needs a tall cruising gear: those are the jobs this set is made for. Yukon part number YG GM8.5-308 is a 3.08 ratio ring and pinion for the GM 8.5 in. and 8.6 in. 10-bolt rear axle, with an 8.50 in. ring gear, 10 ring gear bolts and a 30-spline pinion.
In the 10-bolt the pinion gear rides on two tapered bearings in the nose of the housing and drives the ring gear on the carrier at a right angle. The 3.08 ratio means the driveshaft turns 3.08 times per tire revolution, one of the tallest common ratios for this axle. That keeps engine RPM low at highway speed, which helps fuel economy and noise on a truck or car with stock-size tires and an overdrive transmission. It is the wrong choice for big tires or heavy towing, where a 3.73 or 4.10 does the work better. Many buyers use a 3.08 to return a truck to its factory ratio after the original gears wore out.
Drain the oil and look at the plug and the fluid for metal, then pull the cover and inspect the gear teeth and contact pattern. Pinion bearing wear and gear wear are often found together on these axles. Our GM 8.5 10-bolt problems and rebuild cost guide covers what fails and why, and the 8.5 / 8.6 ring and pinion buyer's guide explains how to identify which 10-bolt you have. Count the ring and pinion teeth or read the RPO code in the glove box to confirm your current ratio.
Yukon lists this gear set for GM 8.5 in. and 8.6 in. rear axles with a 10-bolt cover and 30-spline pinion. That covers the 8.5 in. 10-bolt used under decades of Chevrolet, GMC, Buick, Oldsmobile and Pontiac cars and trucks, and the 8.6 in. version found under late-1990s and 2000s GM half-ton trucks and SUVs. It is not for the smaller 8.2 or 7.5 10-bolts, and the independent-rear 8.6 used in some later cars is a separate design with its own setup specs, so check with us before ordering for an IRS car. Housing casting and pinion spline vary on older axles, so match your cover shape and spline count, or send your year and VIN and we will confirm. Compare the 3.73 face-hobbed 8.5 / 8.6 set if you are running taller tires.
Yukon's set-up chart for the 8.5 and 8.6 lists a 0.037 in. OEM pinion shim, 14-19 in-lb of preload on new pinion bearings, 0.006-0.011 in. backlash, 65 ft-lb on the ring gear bolts and 60 ft-lb on the bearing caps. The 10-bolt uses a crush sleeve for pinion preload; crushing it past spec means starting over with a new sleeve, which is why many builders fit a crush sleeve eliminator kit instead. Replace every bearing, race and seal with the GM 8.5 Timken master overhaul kit, and confirm your carrier accepts a 3.08 ring gear. If you want traction on top of the new gears, a Dura Grip positraction for 30-spline axles drops into the same housing.
Fill with 75W-90 GL-5 gear oil, adding friction modifier with a clutch-type posi. Use the ring and pinion break-in procedure: gentle driving for the first 15 to 20 miles with a cool-down, no hard launches for 100 miles, and a fluid change at 500 miles.
| Brand | Yukon Gear & Axle |
| Part number | YG GM8.5-308 |
| Fits | Yukon Gear High Performance Gear Set For GM 8.5in & 8.6in in a 3.08 Ratio |
| Type | Final Drive Gears |
| Condition | New |
| Ships | Same business day (in stock), from the USA |
| Warranty | 1-year |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
Both use a 10-bolt cover and share this gear set. The 8.6 was the later version under late-1990s and 2000s GM half-ton trucks and SUVs. The axle code, RPO code and cover shape identify it; send your year and VIN if you are unsure.
It is a tall highway ratio. It suits stock-size tires and an overdrive transmission for low cruise RPM. For 33 in. or larger tires, towing or off-road use, a 3.73 or 4.10 is usually the better pick.
The 30-spline count here is the pinion spline, which mates to the driveshaft yoke. Axle shaft spline is set by your carrier, so 28- and 30-spline axle housings can both use this gear set if the housing is an 8.5 or 8.6.
A master overhaul kit with new pinion and carrier bearings, races, seal, crush sleeve and ring gear bolts. A worn yoke seal surface should be replaced at the same time.
75W-90 GL-5. Add friction modifier if the axle has a clutch-type positraction, and change the oil at 500 miles after the new gears are installed.
