Yukon Gear Hardcore Diff Cover for 8.5inch GM Rear w/ 5/16inch Cover Bolts
On a C/K pickup, square-body Blazer, Suburban or GMT400 truck with the GM 8.5 inch 10-bolt rear, the stamped steel cover is usually the first thing to fail off road: one rock or log and it dents into the ring gear, and an old bent flange weeps gear oil onto the exhaust. The Yukon YHCC-GM8.5-S Hardcore cover replaces it with a thick-walled nodular iron cover for the earlier 8.5 housing threaded for 5/16 inch cover bolts. It comes with matching 5/16 inch bolts, a magnetic drain plug and a fill plug, and is finished in black powder coat with a stainless accent plate.
The 8.5 is a C-clip axle with an integral carrier housing: the ring gear, carrier, C-clips and cross pin all sit right behind the cover, and the bottom of the housing is the lowest point on many lifted trucks. A stamped cover does nothing but hold oil. A nodular iron cover acts as armor for the ring gear and any locker or posi you have installed, and it adds stiffness around the open back of the housing so the carrier bearing area flexes less under heavy torque. Yukon shapes the inside so oil flung off the ring gear is guided back across the gears, which helps keep temperatures down when towing. The added drain plug also means future fluid changes no longer require pulling the cover and breaking the seal.
Trace the oil first. A wet pinion area points to the pinion seal, oil inside a rear wheel points to an axle seal, and only a wet cover flange is fixed by a cover. Our cover leak gasket versus RTV guide shows how to read it. Then confirm it is a true 8.5 and not a 7.5 or 8.2, which also have ten cover bolts; the axle code and housing checks are covered in our GM 8.5 10-bolt problems and rebuild cost guide.
This version fits the GM 8.5 inch 10-bolt rear axle with 5/16 inch cover bolt threads, listed for 1972-1998 Chevrolet and GMC C/K and R/V pickups, Blazers, Jimmys, Suburbans, vans, El Caminos and early Silverados, Sierras, Tahoes and Yukons. Yukon flags 1998 and 1999 as transition years: some trucks have 5/16 inch threads and some have 8 mm metric threads, so pull one cover bolt and check it before you order. A 5/16 inch bolt is slightly larger than an 8 mm bolt and uses a coarser thread. If you have the metric housing, order the 8 mm bolt YHCC-GM8.5-M cover instead. Not sure? Send us your year and VIN.
Drain the oil, remove the old cover and scrape the housing face down to bare metal, then clean it with brake cleaner and chase the 5/16 inch holes with a tap. Apply a cover gasket or an even bead of RTV inside the bolt holes, set the cover, start all ten bolts by hand and snug them in a crisscross pattern. Refill through the fill plug with 75W-90 gear oil, and add friction modifier if the axle has a clutch-type posi such as the Yukon Dura Grip for 30-spline 8.5. If the gears howl or the carrier bearings are rough, do them while the cover is off with a GM 8.5 Timken master bearing kit. Trail trucks often pair this cover with a Grizzly locker so the gears and the locker are both protected.
| Brand | Yukon Gear & Axle |
| Part number | YHCC-GM8.5-S |
| Fits | Yukon Gear Hardcore Diff Cover for 8.5inch GM Rear w/ 5/16inch Cover Bolts |
| Type | Diff Covers |
| Condition | New |
| Ships | Same business day (in stock), from the USA |
| Warranty | 1-year |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
Maybe. Yukon lists 1998 and 1999 as years that can have either 5/16 inch or 8 mm cover bolts. Remove one cover bolt and check the thread; 5/16 inch takes this cover, 8 mm takes YHCC-GM8.5-M.
No. Those axles also use ten cover bolts but have a different cover shape. This cover is for the 8.5 inch 10-bolt with 5/16 inch cover bolts.
The nodular iron cover with a stainless accent plate, 5/16 inch cover bolts, a magnetic drain plug and a fill plug.
Use either a quality cover gasket or a thin, continuous bead of RTV on a clean, dry housing face. Let RTV cure as the tube directs before filling.
75W-90 gear oil is typical. If the axle has a clutch-type posi or limited slip, add friction modifier unless the oil already contains it.
