GM 8.5, 8.6 Rear, Horizontal Fins
Part Number 10815

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.

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.

Our thanks to everyone who choose this PML rear axle cover for their truck or SUV and emailed us pictures.

• 2011 Cadillac Escalade EXT


• 2012 Chevy Avalanche 1500
• 2003 Chevy Avalanche Z71
• 2003 Chevy Avalanche Z71 4WD


• 2011 Chevy Silverado 1500
• 2010 Chevy Silverado 1500
• 2007 Chevy Silverado 1500
• 2006 Chevy Silverado 1500


• 2010 Chevy Suburban 1500 4x4 Z71
• 2010 Chevy Suburban 1500


• 2014 Chevy Tahoe 5.3L
• 2008 Chevy Tahoe 5.3L


• 2005 GMC Yukon


• 2006 Hummer H3


• 2007 Sierra 5.3

2011 Cadillac Escalade EXT

Michael installed a polish finish PML differential cover on his Escalade. He put 3 coats of clear coat on it and jb welded a filter magnet to the inside which has 25lbs of holding strength. (Note that we at PML do not think the magnet is needed or necessarily a good idea since a magnet attached incorrectly could cause a lot of problems.) Michael removed some fin material since he had about 1/4" clearance and wanted to be safe if the rubber bushings flexed. Our thanks to Michael for all his feedback and pictures.
     

2012 Chevy Avalanche 1500

David has a 2012 Chevrolet Avalanche 1500 which he uses to tow a travel trailer. He had to replace the bearings in the differential so he wanted to find a better way to drain and replace the fluid to avoid having to replace the bearings again. So he purchased a cast finish PML cover and powder coated it a shiny black.

David had a thermal camera and took thermal images of the stock cover and the PML cover. He took both images after towing a trailer for about an hour on a highway followed by 15 minutes of slower, steady driving. Ambient temperatures were 80F and 70F. David emailed us saying:

"I assumed that the stock differential and axle had plenty of heat-dissipating area, since the oil can flow all the way down both axle tubes.  A few square inches of aluminum fins would not add much.  The thermal images revealed a different story.  The stock differential temperature was mostly 170-200 degrees F while the PML differential was mostly 140-150 degrees F.

Our thanks to David for sharing his thermal images and comments with us. The images are below:

Thermal image of stock differential cover temperatures, from a 2012 Avalanche    Thermal image of PML differential cover temperatures, from a 2012 Avalanche    PML differential cover, custom powder coated shiny black, on a 2012 Avalanche 1500
David installed the PML cover with AMSOIL Severe Gear 75W90, a paper gasket and medium loc-tite on the bolts.
Click on image to view larger.

2003 Chevy Avalanche Z71

Derek installed this PML differential cover on his 2003 Chevy Avalanche. The cover fit nicely behind the pan hard and sway bars. His Avalanche had the 8mm-1.25x21mm stock bolts.

     
Click on image to view larger.

2003 Chevy Avalanche Z71 4WD

Alvin measured and determined this PML cover would fit with pan hard and sway bars and decided on the cast finish. He loves his new PML differential cover.

2003 Avalanche   2003 Avalanche stock differential cover and clearance to sway and pan hard bars   2003 Avalanche with PML differential cover installed   2003 Avalanche with PML differential cover, clears pan hard and sway bars
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2011 Chevy Silverado 1500

Alan installed this PML rear differential cover on his 2011 silverado 1500 4x4 with the 10bolt rear axle. He reused the factory reusable gasket since it is a nice rubber/silicone over steel, as well as zinc plated M8x30 button head screws. This is same size and length that were included with cover. The buttons used are still grade 10.9.

Stock Cover   PML Cover  
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2010 Silverado 1500

Torrance Transmissions in California at 310-378-9217 installed this PML differential cover on a 2010 Chevy Silverado 1500 4x4.

      
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2007 Silverado 1500

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PML differential cover installed on a Chevrolet Silverado 1500. Ed selected the black powder coat finish for his differential cover.

2006 Silverado 1500

This is a picture of a 2006 Silverado 1500 with PML cover installed.

PML Cover Installed
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2010 Chevy Suburban 1500 4x4 Z71

The images below are of Mark & Tahoe's 2010 Z71 Suburban. Our thanks to them for emailing us the pictures. They also commented on the cover: "Fit perfect! Thank you very much!!!"

     
From left to right: 2010 Suburban, Stock Cover, PML Cover Installed
Click on image to view larger.

2010 Chevy Suburban 1500

Ben installed this PML transmission pan on his Suburban. He also installed a PML transmission pan. This Suburban did not have any clearance issues because it is not a police vehicle.

For the installation, Ben removed the track bar and sway bar and modified the brake line bracket just a little, as it is retained by one of the cover bolts. (PML does not recommend this. See a qualified mechanic to ensure brake line safety.)

2010 Suburban 1500   2010 Suburban has clearance for PML differential cover   Another picture of the clearance to the track and sway bars with a PML differential cover on a 2010 Suburban   2010 Suburban PML cover installed
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2014 Chevy Tahoe 5.3L

Georgio installed this PML rear differential cover on his 2014 Tahoe and his 2010 Silverado. His stock bolts were 8mm-1.25x21mm. He also installed a deep PML 6L80 transmission pan on his Tahoe. Our thanks to Georgio for choosing PML covers and pans.

     
Click on image to view larger.

2008 Chevy Tahoe 5.3L

Ian installed this cover on his 2008 Chevy Tahoe 5.3 Maggie TSV1900 supercharged at 12 lbs.

He also installed a PML transmission pan. See PML 4L65E deep pan for info on that pan and installation.

   
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Note that a 2008 Tahoe Police Pursuit Vehicle (PPV) did not have the same clearance. The pan hard bar on the PPV model hit the fins on the PML cover.

2005 GMC Yukon

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PML differential cover installed on a 2005 GMC Yukon SLE. Scott selected the black powder coat finish.

2006 Hummer H3

PML drilled and tapped the cover for a 1/8 NPT. The aftermarket gage and sensor installed in the cover lets this H3 owner track his fluid temperatures while on the road.

PML 10 bolt differential cover on 2006 H3   Temperature sending unit installed in PML differential cover on a 2006 Hummer H3
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2007 Sierra 5.3

Matt installed this PML differential cover on his 2007 GMC Sierra 5.3L.

2007 Sierra 5.3L   Stock Cover   PML Cover   PML cover
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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

 
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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.