Chuck, I copied the blow excerpt from the the wiki page I found. The page is here, http://wiki.planetisuzoo.com/index.php/Troopers
Axles
The Trooper features an independent front suspension design. However, unlike many IFS systems of the era, the design Isuzu utilized is quite strong and will hold up well to abuse. The front differential is one of two different models: the Isuzu Corporate
8-bolt, or the Isuzu Corporate
10-bolt. The 8-bolt was used in Troopers until mid-87, where the entire front suspension was changed and the 10-bolt was incorporated into the design. The 10-bolt front axle was used in Troopers from mid-87 until the final Trooper rolled off of the production line. All Troopers featured front disc brakes.
The rear axles are slightly more varied than the front. The Isuzu Corporate
10-bolt rear axle was used in combination with the
8-bolt front axle in the pre-88 model year trucks. It's not nearly as strong as the 12-bolt and also features drum brakes. In mid-87, the Trooper received a major upgrade to the rear end in the form of the
12-bolt axle. The 12-bolt introduced disc brakes to the rear of the Trooper, providing a boost in stopping power and torque handling in preparation for the 2.6L 4ZE1. Slight modifications were made to the axle design in 1991 (for accomodating the new 4-link coil-spring suspension and wider track of the '92 model year). In 1995 roughly 2 inches was added to the width of the rear axle for the wide-track Trooper (along with longer front axle shafts), although all other features such as spring perches and link mounts remained unchanged. All 12-bolt axles from 1992 through 1997 featured a 4.56 gear ratio. For the 1998 model year, significant changes were made to the axle, including thicker axle shafts and different spline count, resulting in the
Modified 12-bolt axle (with 4.30 gears). Most internal parts of the Modified 12-bolt are not interchangable with the regular 12-bolt axle. Note that the bolt count is the bolts in the ring gear not the pumpkin to the housing.
The Trooper has always had a rather high rear axle ratio. 4.56 (41/9) ring and pinion gear sets were used in the 1984 model Troopers all the way up until around 1998, when 4.30 (43/10) gear sets were used due to the availability of much torquier 3.5 liter V6 engines. The only exceptions to this were the 1986 turbo diesel trooper (it was available for one year only), 4.10 gears were used from the pickup to slow the engine RPM at highway speeds; and the 1989 RS Trooper, which used a 4.77 gear ratio. 4.77 gears were reportedly also available in some 4-door first-generation models with the "Big Tire" option package.
Wheels
The bolt pattern for Troopers is 6x5.5 with a 108mm (4.26") center bore. Many Toyota and Nissan stock wheels will fit, but most GM wheels have center bores that are too small (78mm center bores). Some mid-80's GM trucks and K5 Blazers do have factory wheels with a larger center bore that fit however. Note that the Canyon/Colorado have 6x5.5 bolt patterns with 100mm bores, and Trailblazers/Envoys have 6x5 bolt patterns.
Lugnut sizes is 12x1.5mm with with 60* conical end for factory Isuzu wheels. If using Toyota wheels most Toyota wheels have a stepped shoulder and are hub-centric, that's why they use lugs with straight shank and washers. The Toyota wheels have a large enough hole to fit over the Isuzu hub, but will not center because the diameters are off. Isuzu factory mags are lug-centric and the wheel centers about the lug holes only and not the center hub.
