Eaton Detroit Truetrac Diff 28 Spline 1.20in Axle Shaft Diameter 3.23 & Up Ratio Rear 7.5in/7.625in
The small GM 10-bolt rear, the 7.5 in. and later 7.625 in. axle, ended up under a huge range of late 1980s and 1990s GM cars and light trucks, and almost all of them left the factory with an open differential. If your S-10, Blazer, Camaro, Firebird or G-body spins its right rear tire on a wet launch, or gets stuck on a slick boat ramp with one tire turning, the Eaton Detroit Truetrac 912A317 is the gear-type limited slip that drops into the 28-spline version of that axle with a 3.23 or numerically higher ring gear.
The factory open carrier always gives both axles the same torque, so the tire with less grip sets the ceiling. The Truetrac swaps that carrier for an Eaton steel case with helical pinion gears sitting in pockets around the side gears. When one tire starts to slip, the thrust from those helical teeth presses the pinions into their pockets, and that friction biases torque to the tire that still has traction. There are no clutch discs or preload springs, so there is nothing to wear out and no chatter in tight turns. Eaton lists the 912A317 at 20.85 lb with a 7.5 in. ring gear size, 28 splines and 1.20 in. axle shafts. On a 7.5, which is a light-duty axle to begin with, smooth torque bias rather than the hammer of a locker is easier on the axle shafts and ring gear.
Three things decide fitment on this axle: ring gear size, spline count and ratio. The 7.5 and 7.625 have an oval 10-bolt cover, which is easy to confuse with the 8.5, so measure or check the axle tag. Then pull an axle: early 7.5 axles from 1975-1989 used 26-spline, 1.16 in. shafts, which take a different Eaton unit (911A319 for 3.23 and up), while this one is for 28-spline, 1.20 in. shafts. Finally, count ring and pinion teeth. Eaton catalogs this carrier for 3.23 and up only; the 7.5 uses a different ring gear mounting height for lower ratios, so a 2.73 or 3.08 gear set will not bolt to it. Our GM 7.5 and 7.625 problems guide covers the noises to rule out, and the Truetrac buyers guide lists Eaton's other part numbers by axle.
GM changed spline counts and ratios within model years, and plenty of these axles have been swapped, so send us your year, VIN, RPO axle code and spline count if you want a check before it ships. Other carriers and axle parts are in our hard parts collection.
Still deciding on the type of traction aid? Our Detroit Locker vs Truetrac guide explains how each drives day to day.
| Brand | Eaton |
| Part number | 912A317 |
| Fits | Eaton Detroit Truetrac Diff 28 Spline 1.20in Axle Shaft Diameter 3.23 & Up Ratio Rear 7.5in/7.625in |
| Type | Differentials |
| Condition | New |
| Ships | Same business day (in stock), from the USA |
| Warranty | 1-year |
No. Despite the similar size, this Truetrac is for the GM 7.5 and 7.625 ten-bolt. The Ford 7.5 uses a different carrier.
No. The early 1975-1989 GM 7.5 with 26-spline, 1.16 in. shafts needs a different Eaton unit. This one takes 28-spline, 1.20 in. shafts.
No. Eaton catalogs this carrier for 3.23 and numerically higher ratios. Lower ratios mount the ring gear at a different height and will not fit.
1988-2002 GM half-ton truck rears, 1988-2002 Chevrolet, Pontiac, Buick and Oldsmobile passenger car rears with the 7.5 / 7.625 ten-bolt, and the 1989-1993 Isuzu Rodeo.
No. The Truetrac is a helical gear design with no clutches, so a quality GL-5 gear oil is all it needs.
Carrier bearings and races, ring gear bolts, the pinion seal and a cover gasket at minimum. A 7.5 / 7.625 master overhaul kit covers the pinion bearings too if they are noisy.
