Yukon Gear Chrome Cover For GM 12 Bolt Car

The GM 12-bolt passenger car rear is the axle under a lot of 1960s and early 1970s muscle cars, and plenty of them still wear a pitted, dented or seeping original cover. This Yukon Gear and Axle YP C1-GM12P replaces it with the factory shape in chrome-plated steel. If you own a Chevelle, Camaro, Nova, Impala, El Camino, Monte Carlo, Firebird or GTO with the 8.875 inch 12-bolt and you are looking for a fresh cover after a leak, a regear or a restoration, this is the car version of the part.

What the cover does on a 12-bolt car rear

The 12-bolt car axle uses an 8.875 inch ring gear bolted to the carrier with 12 bolts, and the rear cover closes the center section with 12 cover bolts of its own. That cover is the reservoir wall for the gear oil: the ring gear slings oil off the bottom of the housing onto the pinion bearings and the carrier bearings, and the cover keeps that oil in and road debris out. On the car 12-bolt the fill plug sits in the cover itself, so a cover with a stripped fill hole or a rusted-thin face is more than a cosmetic problem. Yukon builds this one to the stock OE design, so it bolts to an original or reproduction housing with no spacers and no change to the fill level.

Signs the old cover should go

• Oil wetting the bottom of the cover flange or dripping from the lower bolts after you have already resealed it.
• A rounded or cross-threaded fill plug hole in the cover.
• Rust pitting through the paint on the face, or a flange that has been bent by years of overtightened bolts.
• A dent from a jack or a hit that has pushed the face inward toward the ring gear.
• A gear swap, posi install or restoration where you want the axle to look as good as the rest of the car.

How to confirm you have a car 12-bolt

Count the cover bolts first. Twelve bolts on a 1960s or early 1970s GM car usually means the 8.875 inch 12-bolt, while ten means a 10-bolt such as the 8.2 that shared many of the same bodies. Then make sure it is the car axle and not the truck axle: GM built a separate 12-bolt for half-ton trucks, the gears and carriers do not interchange, and Yukon sells a different cover for it. With the cover off, the ring gear should measure close to 8.875 inches. Our GM 10-bolt vs 12-bolt guide walks through casting numbers and the axle code stamped on the tube. If you are chasing a noise rather than a leak, read our whine diagnosis guide before you pull anything apart.

Fitment

Yukon lists YP C1-GM12P for the GM 12-bolt passenger car rear in 1964-1973 Chevelle, 1967-1972 Camaro, 1964-1968 Chevy II, 1969-1972 Nova, 1965-1972 El Camino, 1964-1972 Impala, Bel Air and Biscayne, 1966-1970 Caprice, 1970-1972 Monte Carlo, 1969-1972 Firebird, 1970-1972 GTO and 1964-1970 Buick Wildcat. Not every one of those cars left the factory with a 12-bolt, and many have had axles swapped in the decades since, so go by the bolt count and housing rather than the badge, or send us your year and VIN and we will help match it. Other axle parts are in our hard parts category.

Install notes

• Gaskets and cover bolts are not included. Reuse clean factory bolts or buy a new set, and seal with a cover gasket or a gear-oil-rated RTV. Summit lists a fill plug as included with this cover; a drain plug is not.
• Drain the axle, scrape the housing face to bare clean metal and wipe it dry with brake cleaner. Our gasket vs RTV guide covers bead size and cure time.
• Snug all 12 bolts by hand, then tighten in a crisscross pattern to the factory spec. Chrome steel flanges dimple if you lean on them.
• Fill to the bottom of the fill hole with the vehicle level, using the gear oil grade your manual or gear maker calls for, and add friction modifier if the car has a clutch-type posi. Our fluid change guide covers intervals.

If the cover is coming off because the axle needs work, the 12-bolt car master bearing kit handles worn bearings, the 12-bolt car 3.90 ring and pinion wakes up a highway-geared car, and the Dura Grip posi for 30-spline 12-bolt cars replaces a tired open or worn posi carrier. Worn spider gears alone are covered by the 12-bolt spider gear kit.

Will this cover fit a GM 12-bolt truck axle?

No. The truck 12-bolt is a different housing and Yukon sells a separate truck cover, YP C1-GM12T. This YP C1-GM12P is for the passenger car 12-bolt only.

How can I tell a 12-bolt from a 10-bolt without pulling the cover?

Count the cover bolts. The 12-bolt car rear has 12, the 8.2 and 8.5 10-bolts have 10. Casting numbers and the axle code stamped on the right tube confirm it.

Does it come with a gasket and bolts?

No. Gaskets and cover bolts are not included. Summit lists a fill plug as included with this cover; a drain plug is not. Seal it with a cover gasket or gear-oil-rated RTV.

Is this cover steel or aluminum?

It is chrome-plated steel built to the stock OE shape, so it fits the original housing without clearance changes.

Does it fit a 1999 or later GM truck with a 12-bolt cover?

No. The 12-bolt cover on later GM trucks and SUVs belongs to the 9.5 or 9.76 inch axle, which uses a different cover. This one is for the 1960s and early 1970s 8.875 inch car axle.

What gear oil should I use after installing it?

Use the grade in your service manual or the one your gear or posi maker specifies, commonly 75W-90, and add friction modifier if the car has a clutch-type posi.