USA Standard Ring & Pinion Gear Set For GM 8.5in in a 3.73 Ratio
If your Silverado 1500, Sierra, Tahoe or Suburban howls at 55 mph, or your C10, K5 Blazer, Camaro or Monte Carlo feels flat since the tires got taller, the fix usually lives in the 10-bolt. The USA Standard Gear ZG GM8.5-373 is a new 3.73 ring and pinion for the GM 8.5 and 8.6 inch 10-bolt, with an 8.50 inch ring gear, a 30 spline pinion and 10 ring gear bolts. USA Standard builds these sets to exceed OEM specification and checks them for dimensions, material and fit, which makes it the straightforward choice when you want new gears without paying for a race-grade set.
The driveshaft spins the pinion, the pinion drives the ring gear at a right angle, and the ring gear turns the carrier and both axle shafts. A 3.73 ratio means the pinion makes 3.73 turns for every turn of the axles. In a 10-bolt that is a meaningful step from the 3.08, 3.23 and 3.42 ratios GM fitted to many trucks and cars: more pull from a stop, fewer downshifts with a trailer behind you, and enough multiplication to keep a 4L60E or 6L80 out of its lugging range on 31 to 33 inch tires. The pinion rides on two tapered bearings with preload held by a crush sleeve, and the ring gear sits on the carrier between two side bearings, so gear life depends on those bearings being set correctly.
First confirm you have an 8.5 or 8.6 and not a 7.5, 7.625 or 8.2 10-bolt, which use smaller gears. The cover shape, the ring gear diameter and the axle RPO code all help; our 8.5 and 8.6 ring and pinion buyer's guide shows the differences, and the axle code and ratio guide covers reading the glove box sticker or counting driveshaft turns. If noise is the complaint, separate gear whine from a bearing growl with the accel versus decel whine diagnosis before you spend money on gears. The GM 8.5 10-bolt problems and rebuild cost guide explains what a full regear costs at a shop.
The fitment list for ZG GM8.5-373 is wide. On the 8.6 side it covers 1999-2017 Silverado 1500 and Sierra 1500, 1999-2017 Tahoe, 1999-2013 Yukon, Suburban 1500 and Yukon XL 1500, Avalanche, Escalade, 2002-2009 Trailblazer and Envoy, 2004-2012 Colorado and Canyon, Rainier, Ascender, 9-7x, SSR, 2006-2010 Hummer H3, and Express and Savana 1500 vans. On the 8.5 side it covers 1970s and 1980s rear-drive cars such as the Camaro, Firebird, Nova, Monte Carlo, Cutlass, Grand Prix, Bonneville, Caprice and Impala (through the 1994-1996 B-body cars), plus C10, K10, C1500 and K1500 pickups, the K5 Blazer, G-vans and the 8.5 front axle in many 1977-1991 K-series trucks and Blazers. Axle spline count (28 or 30) changes between years but does not affect this gear set; the carrier and bearings are what you must match. Not every vehicle on that list came with an 8.5 or 8.6, so check the housing or send us your year and VIN. More axle parts are in our hard parts catalog.
Gears are only as quiet as the setup. Plan on new bearings, races, a pinion seal and a crush sleeve (or a crush sleeve eliminator): the Timken GM 8.5 master bearing kit covers the older 8.5, and the USA Standard ZK GM8.6 overhaul kit covers 1999-2008 8.6 axles. Revolution's published 8.5 / 8.6 starting numbers are a 0.037 in. pinion shim, 14-19 in-lb of pinion bearing preload, 0.006-0.010 in. backlash, 65 ft-lb on the ring gear bolts and 60 ft-lb on the caps; treat those as a starting point and set final depth from the contact pattern, as shown in our backlash and pinion depth setup guide. Fill with 75W-90 gear oil, adding friction modifier on a G80 or clutch-type posi. Heat-cycle the new gears gently and change the oil early per the break-in procedure, and on 1999-up trucks and SUVs have the axle ratio reprogrammed so the speedometer and shift points match.
| Brand | Yukon Gear & Axle |
| Part number | ZG GM8.5-373 |
| Fits | USA Standard Ring & Pinion Gear Set For GM 8.5in 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. ZG GM8.5-373 is listed for both the 8.5 and 8.6 inch 10-bolt, with an 8.50 inch ring gear, a 30 spline pinion and 10 ring gear bolts. It does not fit the 7.5, 7.625 or 8.2 10-bolts or the 9.5 and 9.76 12-bolt axles.
On the 8.5 and 8.6 one carrier covers the common street ratios, so a carrier that ran 3.08, 3.23 or 3.42 gears normally accepts this set. Inspect the carrier bearing journals and the spider gears while it is out, and replace a damaged case before you set up new gears.
No. The 28 or 30 spline figure in many fitment tables describes the axle shafts and the side gears, not the ring and pinion. It matters if you are also buying a carrier, posi or axle shafts.
A master install or overhaul kit with new carrier and pinion bearings, races, shims, a pinion seal and a crush sleeve. Reusing old bearings on new gears is the most common cause of noise after a regear.
75W-90 gear oil, plus a friction modifier if the axle has a G80 locker or clutch-type positraction. Change it early, after the break-in miles, to flush out the wear material from new gears.
On 1999 and newer trucks and SUVs the computer uses the axle ratio for the speedometer and shift timing, so have it reprogrammed with a scan tool or tuner. Older trucks with a cable speedometer need a different speedometer driven gear.
