Yukon Gear High Performance Gear Set For GM 8.5in & 8.6in in a 4.56 Ratio
A 4.56 is the ratio most GM half-ton owners land on once a lift and 33 to 35 inch tires have turned a quick truck into a slow one. The Yukon Gear & Axle YG GM8.5-456 is a new 4.56 ring and pinion for the GM 8.5 and 8.6 10-bolt, the axle under 1999-2017 Silverado 1500, Sierra 1500, Tahoe, Yukon and Suburban 1500, the Colorado, Canyon, Trailblazer and Hummer H3, and decades of Chevelles, Camaros, Novas, C10s and K5 Blazers. Yukon lists it with an 8.50 in. ring gear, 10 ring gear bolts and a 30-spline pinion.
The ring and pinion is the last gear reduction before the wheels. With 4.56 gears the driveshaft spins 4.56 times for every turn of the axle shafts, compared with 3.08 or 3.42 in a lot of stock half-tons. That deeper multiplication puts the engine back in its torque band when the tires are taller, cuts the number of downshifts on grades and lets the torque converter stay locked at highway speed. Because a 4.56 still has a reasonably sized pinion head, it is a common middle ground: stronger than a 4.88 in the same housing, but deep enough for a 35 on a V8 truck or a street car with a big cam and a loose converter.
First make sure the housing is an 8.5 or 8.6: a 10-bolt cover with an 8.5 in. ring gear, not the smaller 7.5, 7.625 or 8.2 10-bolt, and not a 9.5 or 9.76 12-bolt. Our 8.5 / 8.6 ring and pinion buyer's guide covers the identification points, and the gear ratio and axle code guide shows how to read the RPO code from the glove box label. Then run your actual tire diameter through the chart in our regear after bigger tires guide. If you are going past 35 inches or have a heavy, built rig, look at the 4.88 version of this gear set instead.
Yukon's fitment table for this part number covers the GM 8.6 rear in 1999-2017 Silverado 1500 and Sierra 1500 (two-wheel and four-wheel drive), 1999-2017 Tahoe, Yukon 1999-2013, Suburban and Yukon XL 1500 through 2014, Escalade, Avalanche, 2004-2012 Colorado and Canyon, Trailblazer and Envoy, Rainier, Ascender, Saab 9-7x, the 2006-2010 H3 and Express and Savana 1500 vans. It also lists the 8.5 rear in 1970s and 1980s GM cars and C and K trucks, and the 8.5 front axle in 1977-1991 K-series pickups, Suburbans and Blazers. On a 4x4, the front must be regeared to 4.56 as well. Axle shaft splines (28 or 30) and housing details vary by year, so confirm against your axle or send us your year and VIN before ordering. The 8.5 carrier series starts at 2.73, so a 4.56 bolts to a stock open carrier, a 30-spline Dura Grip posi or a locker for that series. More parts are in our hard parts catalog.
New gears need new bearings, so plan on a master kit such as the GM 8.5 Koyo master bearing kit. Yukon's published setup figures for the 8.5 and 8.6 are a 0.037 in. starting pinion shim, 14-19 in-lb of new pinion bearing preload, 0.006-0.011 in. backlash, 65 ft-lb on the ring gear bolts and 60 ft-lb on the bearing caps. Read the contact pattern on both the drive and coast sides before buttoning it up; our backlash and pinion depth guide walks through it. A crush sleeve eliminator makes preload easier to hit and to reset later. Fill with 75W-90 gear oil, and add friction modifier if you run a clutch-type posi. Drive easily for the first few hundred miles, avoid towing, and change the oil after break-in. On 1999-and-later trucks, reprogram the ratio and tire size so the speedometer and shift points are correct.
| Brand | Yukon Gear & Axle |
| Part number | YG GM8.5-456 |
| Fits | Yukon Gear High Performance Gear Set For GM 8.5in & 8.6in in a 4.56 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.
For a V8 half-ton that is mostly driven on the street, 4.56 is the usual choice with 35s because it keeps highway rpm reasonable. 4.88 suits heavier, built trucks, lots of towing, or tires larger than 35 inches.
Yes in most cases. GM 8.5 and 8.6 carriers are a single 2.73-and-up series, so the 4.56 ring gear bolts to the same case as the factory gears. Check the case and spider gears for wear while it is apart.
Yukon lists this set for the 8.5 front axle on 1977-1991 K-series trucks, Suburbans and Blazers. Regear the front and rear to the same ratio on any 4x4.
A master bearing kit with new carrier and pinion bearings, races, shims, pinion seal, crush sleeve and ring gear bolts, plus gear oil. Setup needs a dial indicator and an inch-pound torque wrench.
On electronically controlled trucks and SUVs, yes. Use a programmer to enter the new axle ratio and tire size so the speedometer, shift points and ABS work correctly.
