GM 8.5 / 8.6 Rear Differential Cover – Horizontal Fins – Heavy Duty Aluminum Upgrade

Upgrade the performance and protection of your drivetrain with this GM 8.5 / 8.6 Rear Differential Cover with Horizontal Fins, designed to enhance cooling and durability under demanding conditions. The finned design increases surface area to improve heat dissipation, helping maintain optimal differential temperatures during towing, off-road use, and high-performance driving.

Constructed from high-quality aluminum, this differential cover offers superior strength compared to factory stamped covers while providing added protection for internal components. The horizontal fin design not only improves cooling efficiency but also adds a clean, performance-inspired look.

Engineered as a direct-fit replacement for GM 8.5 and 8.6 rear differentials, this cover delivers dependable sealing, durability, and long-lasting performance.

✅ Key Features:

• Fits GM 8.5 and 8.6 rear differentials
• Horizontal fin design for improved heat dissipation
• Heavy-duty aluminum construction for strength and durability
• Provides added protection for internal components
• Ideal for towing, off-road, and performance applications
• Direct fit for easy installation and leak-free sealing

Upgrade your differential with confidence and enjoy improved cooling, enhanced durability, and a performance-driven appearance.

Volume: 0.5 qt. over stock, approximately

Dimensions: Click here for dimensions. 

Number of Bolts: 10 bolts, Guidelines for Bolt Sizes (click here), opens in new tab or window

PML makes two covers for the GM 8.5, 8.6 inch ring gear differential, 10 bolts. This cover has straight horizontal fins and is only 5/8 inch deeper than stock for clearance. For a different look, see PML GM 8.5, 8.6, Vertical Fins differential cover.

Benefits:

• Extra capacity
• Drain hole and magnetic drain plug to simplify maintenance
• Fins for heat dissipation
• Sand cast aluminum construction for thick walls
• Machined gasket flange for a secure seal
• Works with many sway and panhard bars (always check space available)

Note that 8.6 is a short hand reference for the 8.625 or 8 5/8 when written as a fraction.

For a GM 8.2 10 bolt, see 8.2 Rear Differential Cover Info.

Application:

This PML cover fits the GM 8.5, 8.6 rear differential. Many GM, GMC, and Chevrolet vehicles since the 1980s have this. Be aware that for each model and year there may be more than one rear differential possible.

Configurations vary. Always check your vehicle to verify differential and clearance. Some typical vehicles that MAY be able to use this differential cover:

• ½ Ton Trucks, ½Vans and ¾ Vans, 1979 to Current:
  • C10 & K10
  • C1500 & K1500
  • Silverado 1500
  • Sierra 1500
  • Vandura
  • Express & Savana
  • G1500 & G2500
• ¾ Ton Trucks and Vans, 1979 to 1998
  • C20 & K20
  • C2500 & K2500
• Chevy and GM SUVs
  • 1977 to 1994 Full Size Blazer
  • 1977 to 1991 Jimmy
  • 1982 to Current Suburban 1500 (check for panhard bar clearance)
  • 1992 to Current Avalanche 1500, Escalade, Tahoe, Yukon (check for panhard bar clearance)
  • Hummer H3 (check for panhard bar clearance)
• 2002 to 2012 Canyon and Colorado (many models have similar GM Torsen 8.0)

1960s and 70s GM Muscle Cars: some may have a GM 8.2 differential, which is very similar and was used in cars such as Chevelle, GTO, Impala, Monte Carlo and Nova. Check bolt hole pattern carefully. See 8.2 Rear Differential Cover Info.

Police Pursuit Vehicles: generally PPV models have less clearance.

Front Differential: See PML GM Front 8.5 differential cover. This cover is for the rear.

Optional Temperature Sensor Port

The boss on the side can optionally be machined for temperature sending unit. There is a machining charge and a plug is included.

Bolt Information

GM has used four different bolts for this differential. See Guidelines for Bolt Sizes (click here), opens in new tab or window

Gasket Information

PML recommends RTV or paper/fiber gaskets or cork composite gaskets.

PML machines the gasket surface of our differential covers flat. The flange surface of the differential housing is also machined flat. A thin bead of RTV silicon sealant makes an excellent seal between two machined surfaces.

Some of our customers have recommended the Fel-Pro RDS 55028-1 gasket.

PML Differential Cover Compared to Stock

   
Click on image to view larger in a new tab or window.

This image compares the depth of both PML GM 10 bolt differential covers and the stock cover. Click on image to view larger in a new tab or window.