GM 12-Bolt Car Differential Master Overhaul Kit YK GM12P

This is the master overhaul kit for the GM 12-bolt passenger car rear end, the 8.875 inch ring gear axle that went under Chevelles, Camaros, Novas, Impalas and other GM A- and F-body cars through the early 1970s. Yukon part number YK GM12P. It is the full teardown kit, not a minor install kit: carrier bearings and races, pinion bearings and races, pinion seal, a complete pinion depth and carrier preload shim pack, ring gear bolts, pinion nut, crush sleeve, and the oil baffles and slingers where the housing uses them.

Use it when you are swapping ring and pinion ratios, replacing a howling or growling carrier bearing, chasing a leaking pinion seal on a rear end that already has miles on it, or putting a used axle back together after a posi rebuild. Because the shim pack and crush sleeve are included, you can set pinion depth and backlash from scratch instead of reusing tired shims and hoping the old crush sleeve still holds preload. Bearings in the kit are Timken or equivalent quality rather than generic import stock.

Order the right one. The 12-bolt car kit and the 12-bolt truck kit are not interchangeable, even though both use an 8.875 inch ring gear. The truck axle uses a larger pinion and different bearing sizes, so a YK GM12T kit will not fit a car housing and this kit will not fit a truck housing. Identify the housing before ordering: the car 12-bolt has an oval-ish cover with a flat lower section, and the truck cover is noticeably squarer.

Bench notes: set pinion depth first with a dummy shim stack and check your pattern before you crush the sleeve, because once the crush sleeve is collapsed you are into a new one to reset preload. Measure carrier bearing preload with the ring gear off if you are learning the setup. Fill with 75W-90 gear oil and add friction modifier if the axle runs a limited slip carrier.