Motive Gear 3.73 ring and pinion for the GM 8.5 and 8.625 10-bolt axle, 30-spline pinion, for regearing after a tire size change.
Two kinds of GM owners end up shopping for 3.73 gears in a 10-bolt. One just put 33 inch tires on a Silverado 1500, Tahoe or K5 Blazer and now the truck feels lazy off the line and hunts gears on every grade. The other has an 8.5 that started singing at 50 mph after a pinion bearing went loose or the axle ran low on oil. The Motive Gear GM10-373A answers both: a new 3.73 ring and pinion for the GM 8.5 and 8.625 inch 10-bolt with a 30-spline pinion, cut 41 teeth on the ring and 11 on the pinion.
The pinion takes the driveshaft's speed and the ring gear, bolted to the carrier, turns it ninety degrees to the axle shafts. With 41 ring teeth and 11 pinion teeth the driveshaft makes 3.73 turns for each turn of the wheels. Coming from the 3.08, 3.23 or 3.42 ratios common in factory 10-bolts, that is a real change in how hard the truck pulls from a stop and how often the transmission downshifts with a load. Motive cuts this Value A Series set from 8620 steel and heat treats it. It is the 2.73-and-up cut, so it bolts to the standard carrier; a 10-bolt that currently runs 2.56 or another low-series ratio has the thicker carrier and needs a carrier change, not a different gear set.
Make sure the axle is an 8.5 or 8.6 and not the smaller 7.5, 7.625 or 8.2 10-bolt, which use different gears. Count the cover bolts, check the cover shape, and if you can, measure the ring gear. Our GM 8.5 and 8.6 ring and pinion buyer's guide covers the tells, and the axle code and ratio guide shows how to read the RPO sticker or count driveshaft turns to learn your current ratio and carrier series. If noise is the complaint, rule out a carrier or wheel bearing with the acceleration versus coast whine guide before you commit to gears.
This set fits the GM 8.5 inch 10-bolt front and rear and the 8.625 inch 10-bolt rear. That axle went under rear-drive Chevrolet, GMC, Buick, Oldsmobile, Pontiac and Cadillac vehicles from 1970 into the late 2010s, from Chevelles, Camaros, Monte Carlos and G-body cars to C10 and K10 pickups, K5 Blazers, and 1999-up Silverado 1500, Sierra 1500, Tahoe, Yukon and Suburban 1500, plus the 8.5 front axle in many 1977-1991 K-series trucks. Not every vehicle in those lines came with an 8.5 or 8.6, so check the housing. The cross references listed for this set are GM 26037712 and 26066706, Richmond Gear 49-0041-1 and GM85373, Dorman 697-301 and Motive GM10-373. Want a different maker? We also carry the USA Standard ZG GM8.5-373. Send us your year and VIN if you are unsure, and see the hard parts catalog for more axle parts.
This is the gear set only. Budget for new pinion and carrier bearings, races, a pinion seal, crush sleeve, shims and ring gear bolts: the GM 8.5 10-bolt master bearing kit fits the earlier 8.5, and the USA Standard 1999-2008 8.6 overhaul kit fits the later truck axle. Many installers swap the crush sleeve for a solid crush sleeve eliminator on a hard-used axle. Revolution's published GM 8.5/8.6 starting numbers are a 0.037 in pinion shim, 14-19 in-lb of new pinion bearing preload, 0.006-0.010 in backlash, 65 ft-lb on the ring gear bolts and 60 ft-lb on the caps; set final depth from the contact pattern, as shown in our backlash and pinion depth setup guide. Fill with 75W-90 gear oil, add friction modifier if the axle has a clutch-type posi, keep it gentle and tow-free until an early oil change, and on 1999-up trucks have the ratio updated in the computer so the speedometer and shift points read right.
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Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
If it has the 8.6 inch 10-bolt rear, yes. Motive lists the GM10-373A for the GM 8.5 front and rear and the 8.6 rear. Confirm the axle by the cover and RPO code, or send us your VIN.
Yes. This set is the 2.73-and-up cut, so it bolts to a 2.73-and-up carrier. Only a low-series carrier, such as one under 2.56 gears, needs replacing.
No. The 7.5, 7.625 and 8.2 10-bolts use smaller gears. This set is for the 8.5 and 8.625 only.
No. It is the ring and pinion only. Add a master bearing or overhaul kit for your axle year, plus gear oil and friction modifier if you have a posi.
On 1999 and newer trucks and SUVs, yes. Update the axle ratio in the computer so the speedometer, odometer and shift points are correct.
