How To Install a Limited Slip/Posi Unit in a GM 10 Bolt 8.5″ Rear-end

How To Install a Limited Slip/Posi Unit in a GM 10 Bolt 8.5" Rear-end

This video documents the installation of an Eaton Detroit Truetrac Limited Slip/Posi Unit into a 1987 Chevrolet C-10 truck with a 10 bolt 8.5″ Rear-end using a used set of 3.42 gears from a 1988-98 Chevrolet truck — this truck has a 5.3L (325ci) V-8 engine and a 4l80e transmission.

Limited Slip/Posi Unit Install Parts List:

Fitment: 1972 – 1989 GM 10 bolt C-Clip 8.5″ 1.20″ 28 2.73 & up.

The kit says “Ford” in the description, but It fits: Ford 7.5 in./GM 7.5 in./GM 8.2 in./GM 8.5 in

All Eaton differentials made for General Motors 8.5″ and 8.6″ axles require special bearings. For axles with small bearing bores (race O.D. or 2.89″), usually found on vehicles prior to 1999 (like the ones used on the ’87 Chevy truck in this video), the required bearings and races are in the two links below.

For axles with large bearing bores (race O.D. of 3.06″), usually found on newer vehicles from 1999 to present:

3 Quarts Regular GL5 Gear Oil 

Note: No limited slip additive needed for the Eaton Detroit Truetrac unit.

Important Installation Specifications:

  • Ring Gear Bolts (reverse thread) Torque to 65ft lbs
  • Side Bearing Cap Bolts Torque to 60ft lbs
  • Backlash should be .005-.009

Pinion pre-load:

  • New Bearing 14-19in lbs
  • Used Bearing 6-8in lbs

After Installation Burn-Outs and Hard Pulls

Big Smokey Burnout ’87 Chevy Truck 5.3 LS Power

Driving video of this truck with the Welded Differential doing hard pulls…

I took the truck out for some abuse this day to capture some video for everyone. I normally beat on it, but this was more then normal. The truck runs great and has been a blast to drive. No problems at this time with it to report.

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