Timken master bearing kit for the GM 12-bolt car rear (8.875 inch ring gear) with carrier bearings, pinion bearings and races for a gear swap or rebuild.
Your Chevelle, Camaro, Nova or El Camino has a 12-bolt out back and it has started to whine on the freeway, clunk when you stab the throttle, or drip gear oil off the pinion yoke. Or you are about to put a steeper ratio and a posi unit in it and want the bearings fresh before the new gears go in. The Motive Gear R12CRMKT is a master bearing kit for the GM 8.875 in. passenger-car 12-bolt, built around Timken tapered bearings and races for the carrier and both pinion positions along with the small installation parts.
GM brought out the 12-bolt for its performance cars in 1964, and the name comes from the twelve bolts that hold the 8.875 in. ring gear to the carrier. In the center section, the pinion turns on a large inner tapered bearing and a smaller outer one, with a crush sleeve between them that sets preload when the pinion nut is tightened. A shim behind the inner bearing sets pinion depth. The carrier rides on two tapered side bearings, and on this axle the shims that set backlash and carrier preload sit between those bearings and the carrier case. When the bearings wear, preload falls off, the pinion can move under load and the gear pattern walks off center. That is the noise you hear, and it is why fresh gears installed on tired bearings rarely stay quiet.
Pull the cover and look at the oil and the teeth. Metal flakes in the oil or a bearing cage you can see is damaged settles it. Check backlash with a dial indicator and compare it with the 0.006-0.011 in. range Yukon lists for the 12-bolt passenger axle; wide backlash plus yoke play usually means worn pinion bearings. Spin the carrier by hand and feel for a rough spot. Also confirm the axle really is the car version, because the truck 12-bolt uses different bearings.
This kit fits the GM 12-bolt passenger-car rear with the 8.875 in. ring gear, the C-clip axle used under A, F and X-body cars such as the Chevelle, Camaro, Nova and El Camino, and other GM cars of the era. GM installed 12-bolts in cars through 1972. The truck 12-bolt is not the same axle: Chevy Hardcore notes the truck version uses a smaller inner pinion bearing (1.438 in. versus 1.675 in. on the car) and a different ring gear offset, so car and truck kits do not interchange. The kit cross-references to R12CRMK, Richmond 83-1019-1, XL-1019-1, Yukon YK GM12P and 35-2019. Rear ends get swapped between cars a lot over 50-plus years, so verify the housing rather than going by what the car is. You can also send us your details and we will help confirm it. More rear end parts are in our differential hard parts section.
Pull the C-clips and axles, remove the carrier and keep the carrier shims in order by side. Press the old bearings off, drive the races out, install the new Timken races and set pinion depth with your shim, using the old one as a start if the gear set is not changing. Fit a new crush sleeve and tighten the pinion nut gradually, checking rotating drag with an inch-pound torque wrench; Yukon's chart lists 14-19 in-lb with new bearings for the 12-bolt passenger axle, with 55 ft-lb on the ring gear bolts and 60 ft-lb on the caps. Install the carrier with its new bearings, set backlash, then paint the teeth with marking compound and read the pattern before closing it up. This is also the time to install a new gear set, such as the 12-bolt 3.73 ring and pinion, or a Dura Grip positraction for 30-spline axles. Fill with 75W-90 gear oil and add friction modifier if the axle has a clutch-type posi. If an open carrier stays, worn side gears are covered by the 12-bolt spider gear kit.
| Fits | GM 12-bolt passenger car rear, 8.875 inch ring gear |
| Part number | Motive Gear R12CRMKT |
| Bearings | Timken tapered carrier and pinion bearings with races |
| Interchange | R12CRMK, Richmond 83-1019-1, XL-1019-1, Yukon YK GM12P, 35-2019 |
| Includes | Bearings, races and installation small parts |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
No. The truck 12-bolt uses a smaller inner pinion bearing and a different ring gear offset than the car version, so it takes a different kit. This one is for the 8.875 in. passenger-car 12-bolt.
Timken tapered carrier bearings, front and rear pinion bearings and their races, with installation small parts such as the crush sleeve, pinion seal, pinion nut, marking compound and brush. Gears, carrier and axle bearings are not included.
It is listed as interchanging with R12CRMK, Richmond 83-1019-1, XL-1019-1, Yukon YK GM12P and 35-2019, so it serves the same axle. Exact contents vary slightly by brand.
Yukon's chart for the 12-bolt passenger axle lists 14-19 in-lb of pinion preload with new bearings, 0.006-0.011 in. backlash, 55 ft-lb on the ring gear bolts and 60 ft-lb on the bearing caps.
75W-90 gear oil. If the axle has a clutch-type posi or limited slip, add friction modifier unless the oil already contains it.
