X88 expeditions - Documenting and sharing overland travels, adventures, and expeditions

March 27, 2007

Going For The 4•5•6 - Background

Through many previous online discussions, taking measurements, and heavy research, it has been determined that the TrailVoy (GM360) platform uses 3 different rear axles:
  • 8" for the short wheelbase I6 vehicles
  • 8.6" for the short wheelbase V8 vehicles
  • 8.6" for the long wheelbase vehicles - both I6 and V8
  • 9.5" for the LS2 V8 (6.0L) vehicles

This modification/upgrade is completely based on the assumption that other than the gear sizes and maybe the size of the gear housing, the other axle attributes (control arm mounting points, brakes, bearings, etc.) are the same between 8" and 8.6" axles and that the 8.6 will mount properly under my Trailblazer.

So why go through all this trouble? Well, three main reasons:

  • After upgrading to 33" off-road tires, I experienced a noticeable power loss using the stock 3.42 gear set. Upgrading to 4.56 gears will bring that power back and according to numerous online sources, 4.56 is in the "sweet spot" for 33" tires.

  • There are no aftermarket lockers available for the 8" axle, only the stock GM/Eaton "gov-lock" mechanical locker. A capable unit but one that I already broke on the blue Trailblazer. Going to the 8.6" axle opens up a whole world of aftermarket lockers - mechanical, air, or electronic.

  • The 8" axle uses shafts with 28 splines. The 8.6" axle uses shafts with 30 splines which is inherently stronger and more robust.

Here are some pictures that were used during the online discussion and measurement phase of the research.

You may be asking: why stop at a 4.56 gear ratio? Why not go even higher for more power? Well, that has to do with the realities of the Trailblazer front axle and differential. More on that later.