Yukon Gear High Performance Gear Set For GM 8.5in & 8.6in in a 3.73 Ratio
The 3.73 is the all-round ratio for a GM 10-bolt: deep enough to tow and to wake up a half-ton on 33 inch tires, but still livable on the highway with an overdrive transmission. Buyers looking at the Yukon Gear & Axle YG GM8.5-373 usually drive a Silverado, Sierra, Tahoe, Suburban or Yukon with an 8.6 rear that is whining or struggling with bigger tires, or a Camaro, Chevelle, Nova or C10 with an 8.5 that needs more launch. This is a new 3.73 ring and pinion with an 8.50 in. ring gear, a 30-spline pinion and 10 ring gear bolts.
The pinion rides on two tapered bearings in the nose of the housing and turns the ring gear at a right angle; the ring gear bolts to the carrier, which drives the axle shafts. At 3.73 the driveshaft turns 3.73 times for each tire turn. Compared with a 3.08 or 3.42, that multiplies torque noticeably, so a truck pulls a trailer or tall tires without constant downshifts, and a muscle car leaves the line harder. Highway rpm goes up, but with a four-speed or six-speed automatic it stays reasonable.
Drain the oil, look at the drain plug and the fluid for metal, then pull the cover and inspect the teeth and the contact pattern. Pinion bearing wear and gear wear often show up together on high-mile 10-bolts, and our GM 8.5 10-bolt problems and rebuild cost guide explains what fails and what a rebuild involves. To confirm the axle and current ratio, check the RPO codes on the glove box or door sticker, or count ring and pinion teeth. The 8.5 / 8.6 ring and pinion buyer's guide covers telling an 8.5 or 8.6 apart from the 7.5, 7.625 and 8.2 10-bolts, which take different gears.
Yukon's fitment list for this set is long. On the 8.6 side it includes 1999-2017 Silverado 1500 and Sierra 1500, Tahoe and Yukon, Suburban and Yukon XL 1500, Avalanche, Escalade, 2002-2009 Trailblazer and Envoy, Colorado and Canyon, Hummer H3 and Express and Savana 1500 vans. On the 8.5 side it covers 1970s and 1980s cars such as the Camaro, Firebird, Chevelle, Nova, Monte Carlo, Cutlass, Grand Prix and Caprice, plus C10, K10, C1500 and K1500 pickups and the K5 Blazer. Yukon also lists it for the 8.5 front axle on several 1977-1991 K-series trucks and Blazers. It does not fit 8.6 IRS cars, the 7.5, 7.625 or 8.2 10-bolts, or the larger 9.5 and 9.76 axles. Axle spline count and carrier type vary by year, so match the housing, or send your year and VIN for a check. Yukon sells the standard open 8.5 carrier for 2.73 and higher ratios if your carrier is damaged.
Yukon's setup chart lists the 8.5 / 8.6 with 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. Use those as starting points and set final depth from the contact pattern. Replace every bearing and race with the GM 8.5 Timken master overhaul kit, or, if you are installing an aftermarket posi with larger carrier bearing journals, the Yukon kit for 8.5 axles with aftermarket positraction. The pinion preload is set with a crush sleeve, so many installers fit the crush sleeve eliminator instead.
Fill with 75W-90 GL-5 gear oil, adding friction modifier for a clutch-type locker or posi. Break the gears in with easy driving and no heavy towing for the first few hundred miles, then change the oil at 500 miles as described in our ring and pinion break-in procedure. On trucks and SUVs from 1999 on, reprogram the axle ratio in the computer so the speedometer and shift points are correct.
| Brand | Yukon Gear & Axle |
| Part number | YG GM8.5-373 |
| Fits | Yukon Gear High Performance Gear Set For GM 8.5in & 8.6in in a 3.73 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.
Yes, if it has the 8.6 in. 10-bolt rear, which Yukon lists for 1999-2017 Silverado 1500 trucks. Some half-tons were built with the 9.76 in. 12-bolt instead, so check the RPO codes or count the cover bolts before ordering.
For many half-ton trucks with stock gearing near 3.08 or 3.42, 3.73 brings back much of the lost performance on 33s. For 35 inch tires most owners go deeper, to 4.10 or more.
Usually not. Yukon's standard open 8.5 carrier is listed for 2.73 and higher ratios, so a 3.73 set normally bolts to the carrier already in the axle. Inspect the carrier and side gears for wear while it is out.
A master overhaul kit with bearings, races, shims, crush sleeve and pinion seal, a new cover gasket, and 75W-90 gear oil. Add friction modifier if the axle has a clutch-type posi or locker.
No. The independent rear 8.6 used in some later GM cars is a different design. This set is for the solid-axle 8.5 and 8.6 10-bolts and the 8.5 front axles Yukon lists.
On electronically controlled trucks and SUVs, yes. Update the axle ratio with a programmer so the speedometer, shift points and ABS use the correct values.
