Eaton Detroit Truetrac Differential 30 Spline 1.32in Axle Shaft Dia 2.73 & Up Ratio Rear 8.5in/8.6in
The GM 8.5 and 8.6 10-bolt under late-1980s through 2000s Chevy and GMC half-tons, Tahoes, Suburbans, vans and Hummer H3s usually came with either an open carrier or the factory clutch-style G80 locker. Both leave owners stuck: the open unit spins one tire on wet boat ramps and snowy driveways, and a tired G80 bangs or simply stops engaging. The Eaton Detroit Truetrac 913A481 is a helical-gear limited slip carrier for this axle with 30-spline, 1.32 inch axle shafts and a 2.73 or numerically higher ring gear ratio.
Inside the steel case, each axle shaft splines into a helical side gear, and pairs of helical pinions ride in pockets around them. When both tires have grip, the gears simply let the wheels turn at different speeds in a turn, so the truck drives like it has an open differential. When one tire starts to slip, the separating force of the helical teeth jams the pinions against their pockets, and that friction sends more torque to the tire that can still pull. It happens automatically, in forward and reverse, with no clutch plates, springs or flyweights to wear out. That is the main reason people pick it over a replacement G80: there is nothing inside that ratchets, slams or needs a rebuild later.
Check three things. First, the axle: the 8.5 and 8.6 both have a 10-bolt cover, but so do the smaller 7.5, 7.625 and 8.2, so measure the ring gear or check the axle code and RPO on the glovebox sticker. Second, the spline count. This unit is the 30-spline, 1.32 inch version; most 1970s and 1980s car and truck 8.5 axles use 28 splines and need the 28-spline Truetrac 912A556 instead. Third, the ratio must be 2.73 or numerically higher. If you would rather have clutch-type bite, compare the Eaton Posi for the same axle, and for full locking off-road look at the Grizzly Locker.
Eaton's product selector lists 913A481 for the rear GM 10-bolt C-clip axle in 1988-1996 GM passenger cars, 1988-2007 half-ton trucks and vans and 1988-2013 three-quarter-ton applications with this axle, plus the rear 8.6 in 2005-2007 Saab 9-7x and 2006-2009 Hummer H3. Ring gear size is 8.5 inches and the unit weighs about 26 pounds. GM used more than one axle under the same nameplate, so verify the 10-bolt, the 30-spline shafts and your ratio before ordering, or send us your year and VIN and we will confirm it.
Eaton's catalog note is the part people miss: every Eaton carrier for the GM 8.5 and 8.6 needs specific carrier bearings. Small-bore housings (2.89 in. race outside diameter, usually before 1999) take bearing LM102949 with race LM102911, and large-bore housings (3.06 in. race OD, usually 1999-2013) take LM603049 with race LM603012. Measure the old race before you buy a kit. Yukon's HD carrier installation kit is made for aftermarket carriers like the Truetrac, and a master overhaul kit for HD posi or locker covers the pinion side too. Torque ring gear bolts to 65 ft-lb with thread locker and bearing caps to 60 ft-lb, and recheck backlash at 0.006-0.010 in. because the new case can shift the ring gear. Fill with 75W-90 GL-5 gear oil. No friction modifier is needed. Expect a few hours of work with the axles out and the C-clips removed.
| Brand | Eaton |
| Part number | 913A481 |
| Fits | Eaton Detroit Truetrac Differential 30 Spline 1.32in Axle Shaft Dia 2.73 & Up Ratio Rear 8.5in/8.6in |
| Type | Differentials |
| Condition | New |
| Ships | Same business day (in stock), from the USA |
| Warranty | 1-year |
Yes, if the axle is the 8.6 10-bolt with 30-spline shafts and a 2.73 or higher ratio, which covers most 1999-2007 half-ton G80 trucks. Eaton lists 1988-2007 half-tons for 913A481. Use large-bore LM603049/LM603012 carrier bearings on those housings.
No. It has no clutch packs, so plain 75W-90 GL-5 gear oil is correct. Friction modifier is only for clutch-type limited slips.
Yes. Eaton rates it for 2.73 and numerically higher ratios, which takes in 3.08 through 4.56 and similar gear sets for the 8.5 and 8.6.
A helical limited slip needs some load on both tires to build bias. With one wheel completely unloaded it can spin like an open diff; a light touch on the brake pedal often brings it back. For rock crawling with lifted tires a full locker is the better tool.
The carrier is the same part number, but the bearing size often changes. Eaton says small-bore housings usually came before 1999 and large-bore housings from 1999-2013, so measure the race before ordering bearings.
