Yukon Gear Chrome Cover For GM 12 Bolt Truck

Square-body and earlier GM half-tons spent decades on salted roads, and the stamped cover on the 12-bolt truck rear is usually the first thing to rot. This Yukon Gear and Axle YP C1-GM12T is a chrome-plated steel replacement made in the stock truck shape. It is for the 8.875 inch 12-bolt under 1963-1987 Chevrolet and GMC C10, K10, C15/C1500 and K15/K1500 pickups, Blazer and K5 Blazers, Suburbans and G10/G15 and G20/G25 vans. If you are restoring a C10 or resealing a leaky K5 rear, this is the truck cover, not the car one.

What the cover does on a 12-bolt truck rear

Like the car axle, the truck 12-bolt carries an 8.875 inch ring gear and closes the center section with a 12-bolt cover, but the housing, gears and carriers are truck-specific and do not swap with the passenger car parts. The cover holds the gear oil pool the ring gear dips into and throws onto the pinion and carrier bearings, and it is the only thing between the gears and whatever the truck drives through. Unlike the car version, the truck housing is filled through a plug in the housing rather than the cover, which is why Summit lists no fill plug with this part. Yukon makes it to the original design, so it lines up with the factory bolt holes and seals against the stock housing face.

Signs the cover is done

• Gear oil seeping from the lower half of the cover flange onto the frame crossmember or exhaust.
• Rust holes or heavy scaling on the face, common on trucks that lived in snow states.
• A caved-in face from a rock, a stump or being used as a jacking point.
• Elongated or torn bolt holes in the flange that will not hold torque.
• A gear change or locker install on a frame-off build where the old cover is not worth reusing.

How to confirm you have the truck 12-bolt

Count 12 cover bolts, then check the year. On a 1960s through 1987 half-ton, a 12-bolt cover almost always means this 8.875 inch truck axle. Yukon lists it for both two-wheel-drive and 4x4 versions, and many of these trucks rolled on six-lug wheels. A 12-bolt cover on a 1999 or later GM truck is a different axle, the 9.5 or 9.76 inch, and needs a different cover; our GM 9.5/9.76 12-bolt guide covers that one. For telling the truck axle from the car axle and the 10-bolts, see our 10-bolt vs 12-bolt guide. A wet cover can also be confused with a leaking pinion seal; the leak checks in our pinion seal guide help sort that out.

Fitment

Yukon lists YP C1-GM12T for the GM 12-bolt truck rear in 1963-1986 Chevrolet C10 and K10 pickups, 1967-1986 K10 Suburban, 1963-1966 Suburban, 1969-1974 Blazer and 1975-1986 K5 Blazer, 1967-1981 G10 vans, and 1987 R10, V10, V10 Suburban and Blazer. On the GMC side it covers 1966-1978 C15 and K15, 1979-1986 C1500 and K1500 pickups and Suburbans, 1964-1966 and 1979-1987 G1500, 1967-1978 G15 and G25, and 1979-1981 G2500 vans, and the 1987 R1500 and V1500. GM used 10-bolt rears in many of these trucks too, so the bolt count matters more than the model year. If you are unsure, send us the year, VIN and a photo of the cover. Other axle parts are in our hard parts category.

Install notes

• No gasket, cover bolts, fill plug or drain plug come with it. Plan on a cover gasket or gear-oil-rated RTV and clean or new bolts.
• Pull the housing fill plug before you drain, so you know you can refill. Clean the housing face completely; old gasket material left behind is the usual cause of a repeat leak. Our cover leak guide explains both sealing methods.
• Run the bolts down evenly in a crisscross order to the factory torque. A thin chrome flange will bow if one bolt is pulled tight first.
• Refill through the housing plug to the bottom of the hole, using the gear oil your manual specifies, plus friction modifier for a clutch-type posi.

If the rear is being opened up anyway, the 12-bolt truck master overhaul kit renews the bearings and seals, the Yukon 3.73 gear set for the 12-bolt truck replaces chipped or noisy factory gears, and the Timken 12-bolt truck master bearing kit is the bearing-only option. When new gears go in, the Allstar 12-bolt truck ring and pinion installation kit supplies the shims, crush sleeve and seal for setup.

Is the truck 12-bolt cover the same as the car 12-bolt cover?

No. GM built separate car and truck 12-bolt axles, and Yukon sells separate covers. This YP C1-GM12T is for the truck; the car rear uses YP C1-GM12P.

Will it fit my 1999 or newer Silverado with a 12-bolt cover?

No. That truck has the 9.5 or 9.76 inch axle, which uses a different cover. YP C1-GM12T is for 1963-1987 half-ton trucks, Blazers, Suburbans and vans with the 8.875 inch 12-bolt.

Where does the fill plug go on this axle?

The truck 12-bolt fills through a plug in the housing, not the cover. Summit lists no fill or drain plug with this cover, so reuse the plug in your housing.

Are a gasket and bolts included?

No. Buy a cover gasket or use gear-oil-rated RTV, and reuse clean factory bolts or a new set.

My K10 has a 10-bolt rear. Will this fit?

No. Many GM trucks of these years came with a 10-bolt rear instead. Count the cover bolts; this cover needs the 12-bolt housing.

How much gear oil does it take after the cover is changed?

Fill with the vehicle level until oil reaches the bottom of the housing fill hole, using the gear oil grade in your service manual.