Yukon Gear High Performance Gear Set For GM 8.5in & 8.6in in a 3.42 Ratio
A 3.42 is one of the most common ratios GM put in its 10-bolt trucks and SUVs, so most people shopping for the Yukon Gear & Axle YG GM8.5-342 are replacing worn factory gears without changing the ratio: a Silverado or Sierra 1500, Tahoe, Suburban or Yukon whose 8.6 rear has started to howl, or a Camaro, Nova, Chevelle or C10 with a tired 8.5. Others are stepping up from 2.73 or 3.08 gears for a little more pull with slightly larger tires. This is a new ring and pinion with an 8.50 in. ring gear, a 30-spline pinion and 10 ring gear bolts.
The 8.5 and 8.6 are semi-floating 10-bolt axles. The pinion is supported by two tapered roller bearings in the nose of the housing, and it drives the ring gear bolted to the differential carrier. With a 3.42 set, the driveshaft makes 3.42 turns for every turn of the rear tires. That is a middle ground: noticeably livelier than a 3.08 or 3.23 when pulling away or carrying weight, while keeping highway rpm low enough for good fuel economy with an overdrive automatic. Because it matches many stock gear sets, swapping it in on a truck that already had 3.42s does not change speedometer calibration or shift points.
Gear whine can be confused with wheel bearing and tire noise. A gear noise changes with load (on throttle versus coasting) at the same speed, while a bearing noise tends to change when you steer side to side. Pull the cover and look at the teeth and the oil. Our GM 8.5 10-bolt rear end problems guide walks through the common failures and rebuild costs. To verify your current ratio, read the axle RPO code on the glove box or door label (GU6 is the code GM used for 3.42) or count the ring and pinion teeth, as covered in how to find your rear axle gear ratio.
Yukon lists this set for the 8.6 rear in 1999-2017 Silverado 1500 and Sierra 1500, Tahoe, Yukon and Escalade, Suburban and Yukon XL 1500, Avalanche, 2002-2009 Trailblazer, Envoy, Rainier and Ascender, 2004-2012 Colorado and Canyon, Hummer H3 and Express and Savana 1500 vans. On the 8.5 side it covers 1970s and 1980s cars including the Camaro, Firebird, Nova, Malibu, Monte Carlo, Grand Prix, Caprice and Impala, the C10, K10, C1500 and K1500 pickups, the K5 Blazer and Suburbans, and 8.5 front axles on 1977-1991 K-series trucks and Blazers. Yukon also lists the 1994-2004 S10 and Sonoma; most of those compact trucks were built with a smaller 10-bolt, so confirm yours is an 8.5 first. The Oldsmobile-design 8.5 rear is a different axle and needs an Olds-specific gear set instead. If you are unsure, count the cover bolts and measure the ring gear, or send us your year and VIN. More 10-bolt parts are on the rebuild kits page.
Yukon's setup chart for the 8.5 and 8.6 calls for 14-19 in-lb of preload on new pinion bearings, backlash in the 0.006-0.011 in. range, 65 ft-lb on the ring gear bolts and 60 ft-lb on the bearing caps, with 0.037 in. as the typical OEM pinion shim. Set pinion depth, then preload, then backlash, and read the pattern on both drive and coast sides. Never reuse old pinion bearings with new gears; the GM 8.5 Timken master overhaul kit includes the bearings, races, shims, crush sleeve and seal. If the carrier is a clutch-type posi with worn clutches, rebuild or replace it now, for example with a Dura Grip positraction for 30-spline axles. Finish with a fresh cover seal or a GM 8.6 rear cover kit. Refill with 75W-90 GL-5 gear oil plus friction modifier if the axle has a limited slip, take it easy for the first 500 miles and change the oil after that, following our ring and pinion break-in guide.
| Brand | Yukon Gear & Axle |
| Part number | YG GM8.5-342 |
| Fits | Yukon Gear High Performance Gear Set For GM 8.5in & 8.6in in a 3.42 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.
No. If you are replacing 3.42 gears with this 3.42 set, the speedometer, shift points and ABS calibration stay correct. Reprogramming is only needed when the ratio changes.
Look at the RPO label in the glove box or on the door. GU6 is the code for a 3.42 axle ratio. You can also count the ring and pinion teeth with the cover removed.
Yukon lists the 8.6 rear in Tahoe models through 2017 for this set. Confirm that your truck has the 10-bolt 8.6 axle and not a 9.76 or 9.5 12-bolt before ordering.
It can be acceptable on a light truck with a modern six-speed automatic, but most owners who move to 33 inch tires choose 3.73 or 4.10 to restore performance. 3.42 is best for stock or near-stock tire sizes.
Pinion and carrier bearings, races, shims, a crush sleeve, the pinion seal and the cover gasket. A master overhaul kit covers most of these. Use 75W-90 GL-5 gear oil.
