Motive Gear GM10-342A 3.42 ring and pinion plus R10RMK master bearing kit for GM 8.5 and 8.625 in 10-bolt axles. Full regear in one box.
This package is for the GM 10-bolt owner who wants one order to cover the whole regear: a Motive Gear GM10-342A 3.42 ring and pinion and a Motive R10RMK master installation kit in the same box. It is a popular swap for a C10, K1500, K5 Blazer, Camaro, Chevelle or Nova that came with a 2.73 or 3.08 and feels lazy off the line, and a clean replacement when the factory 3.42 gears in a high-mileage 8.5 have started to whine.
The GM 8.5 sets its final drive with a hypoid ring gear bolted to the carrier and a pinion driven by the driveshaft. The GM10-342A has 41 ring gear teeth and 12 pinion teeth (41 divided by 12 is 3.42), an 8.5 in. ring gear and standard rotation, and Motive makes it from 8620 steel as part of its Value A Series. Compared with a 2.73 or 3.08, a 3.42 multiplies torque by roughly 11 to 25 percent more at the wheels, so the truck or car pulls harder from a stop, tows with fewer downshifts and makes better use of a modest tire upgrade, while still cruising at sensible highway rpm. The 12-tooth pinion is also a larger, stronger pinion head than the ones used in deep 4.56 and 4.88 sets.
Make sure the housing is a GM 8.5 or 8.6 10-bolt and not a 7.5, 7.625 or 8.2, which look similar from outside. Our GM 10-bolt ring and pinion buyer's guide and the 8.5 rear end problems and rebuild cost article cover identification and noise diagnosis. Read the ratio code from the glove box label or count teeth, and pick the ratio with the help of our tire size and gear ratio guide. If you want a heat-treated performance set in the same ratio, the Yukon 3.42 gear set for the 8.5 and 8.6 is the alternative.
JEGS catalogs the GM10-342A for the GM 8.5 10-bolt front and rear and the 8.6 10-bolt rear, and the R10RMK kit for the 8.5 front and rear, including 4WD front axles from 1977-1991. That covers a long list of GM cars, C and K pickups, Suburbans, Blazers and vans. Late 8.6 (8.625) rears in 1999-and-newer trucks and SUVs often take different pinion bearings, and Motive sells a separate R10RLMK master kit for the 8.625; for those, see our GM 8.6 ring and pinion and master kit package. Spline counts and housing details vary by year, so check your bearing numbers, or send us your year and VIN to confirm. More axle parts are in our rebuild kits category.
The R10RMK includes the carrier and pinion bearings, shims, a crush sleeve, the pinion seal and nut, ring gear bolts, the cover gasket and marking compound. Set pinion depth with shims under the inner pinion bearing, then tighten the pinion nut slowly to crush the new sleeve until rotating preload is in spec; overshooting means starting again with a new sleeve. Shim the carrier for backlash and side bearing preload, then read the pattern with the compound. If the original 2.73-and-up carrier is worn, a new GM 8.5 open carrier case takes this ring gear. A bearing puller and seal driver kit makes removing the old pinion bearing easier. Fill with 75W-90 gear oil plus friction modifier for a clutch posi, drive gently for a few hundred miles, and change the oil after break-in.
| Axle | GM 8.5 in and 8.625 in 10-bolt |
| Ratio | 3.42 (41/12 teeth) |
| Gear set | Motive Gear GM10-342A, standard rotation |
| Install kit | Motive Gear R10RMK master kit with Koyo bearings |
| Ring gear diameter | 8.5 in |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
A Motive Gear GM10-342A 3.42 ring and pinion and a Motive R10RMK master installation kit with carrier and pinion bearings, shims, crush sleeve, pinion seal and nut, ring gear bolts, cover gasket and marking compound.
The gear set fits the 8.6, but many 1999-and-later 8.6 rears use different pinion bearings than the R10RMK kit. Compare your bearing numbers or send us your VIN; the R10RLMK kit is the usual match for those trucks.
It is a common step up from 2.73 or 3.08 for a mild tire upgrade or regular towing. For 33 inch and larger tires, most truck owners go deeper, such as 3.73 to 4.10 or more.
Usually not. GM 8.5 carriers are one 2.73-and-up series, so the ring gear bolts to your existing case if it is in good shape.
Drive normally without heavy loads or towing for the first few hundred miles, avoid long full-throttle runs, then drain and refill the gear oil to remove break-in wear particles.
