Eaton Detroit Truetrac Differential 30 Spline 1.31in Axle Shaft Dia 3.92 & Up Ratio Rear Dana 44
A rear Dana 44 with 30-spline shafts sits under a lot of four-wheel drives that people still drive hard: TJ Wranglers, Cherokees and Wagoneers, International Scouts and late-1970s Ford half-tons. Once those trucks get bigger tires and a deeper ratio, the open carrier becomes the weak spot, lifting one rear tire on a ledge or spinning it on a wet boat ramp. The Eaton Detroit Truetrac 913A590 is a gear-type limited slip built for exactly that axle: Dana 44 rear, 30 spline, 1.31 inch shafts, 8.5 inch ring gear, and ratios of 3.92 and numerically higher.
Instead of clutch packs, the Truetrac carries helical side gears and pinions in pockets machined into the case. Cruising and turning, it behaves like an open differential, so it is quiet and the rear tires do not scrub in parking lots. When one tire starts to lose grip, the helical gears load up against their pockets, and that friction moves torque toward the tire that can still pull. Eaton and its distributors describe it as automatic, with no driver input and nothing that wears like clutch plates. For a rear Dana 44 that means a trail Jeep that keeps walking forward on loose climbs and a daily driver that still feels normal on pavement.
Three facts decide it: axle model, spline count and the carrier break. Read the axle tag or count the cover bolts and look for the Dana 44 casting, then pull a shaft and count splines; 30 spline at 1.31 inch is the common rear. The Dana 44 carrier break falls between 3.73 and 3.92, so 3.92-and-deeper gears mount on a different case than 3.73-and-taller gears, and the two do not interchange. Eaton notes this unit is for non-thick ring gears. If your axle has 3.54 or 3.73 gears and you are keeping them, order the 3.73-and-down rear Truetrac instead. Our carrier break explainer walks through it, and the Dana 44 problems and rebuild guide covers the bearing noise that often shows up at the same time.
Eaton's application selector for 913A590 lists rear Dana 44 axles in 1971-2006 Jeeps (its Jeep group names the Cherokee, Grand Cherokee, Wagoneer, Scrambler and Wrangler), 1967-1980 International Harvester half-tons and Scouts, and 1977-1979 Ford half-ton trucks, vans and SUVs, all at 3.92 and up. The 2007-2018 JK and later JL rears are not in that list; the JK Dana 44 uses one carrier for every ratio, so it takes a different unit. Dana 44s also came with 19, 32 and other spline counts, so count yours rather than going by the vehicle alone. If you are unsure, send us the year, VIN and axle tag before ordering. Front axles take the separate front Dana 44 Truetrac, and the rest of our differential parts are in hard parts.
Treat this as a carrier swap that has to be set up, not a bolt-in. Move the ring gear to the new case using new or clean ring gear bolts with thread locker, press on carrier bearings (plan on new ones), and use the existing shims as a starting point. Check backlash and the gear pattern before closing it up; Dana 44 carrier shims sit behind the bearings, and a carrier shim driver tool keeps them from getting chewed up. If you are regearing at the same time, a complete TJ gear and install kit covers the bearings, seals and shims in one box. Fill with a quality GL-5 gear oil: the Eaton guidance printed on our distributor's listing calls for petroleum (mineral) GL-5, allows synthetic where the axle maker approves it, and says not to add friction modifier because it reduces Truetrac performance. Our Truetrac buyer's guide has more on matching splines and ratios.
| Brand | Eaton |
| Part number | 913A590 |
| Fits | Eaton Detroit Truetrac Differential 30 Spline 1.31in Axle Shaft Dia 3.92 & Up Ratio Rear Dana 44 |
| Type | Differentials |
| Condition | New |
| Ships | Same business day (in stock), from the USA |
| Warranty | 1-year |
No. Dana 44 ratios split into two carriers, 3.73 and numerically lower on one and 3.92 and higher on the other. With 3.73 or 3.54 gears you need the 3.73-and-down rear Truetrac. This unit is for 3.92 and up, non-thick ring gears.
It is not listed for the 2007-2018 JK or the JL. Eaton's selector for 913A590 covers 1971-2006 Jeep rear Dana 44s, Scouts and 1977-79 Ford half-tons. JK and JL axles take different Truetrac part numbers.
No. The Truetrac has no clutch plates. The lubrication guidance says to use GL-5 gear oil, mineral based or synthetic if the axle maker approves, and not to add friction modifier because it reduces how well the gears bias torque.
A gear-type limited slip needs some resistance at both tires to build torque. With one tire completely in the air it can still spin; many owners lightly drag the brakes to load it. If you need both tires driving with no traction at one, a full locker such as an ELocker is the better tool.
Carrier bearings, the pinion seal and the cover gasket at a minimum, and new ring gear bolts. If the pinion bearings are noisy or the gears show wear, do a full master install kit with the regear.
No. Eaton catalogs the rear Dana 44 3.92-up unit as 913A590 and the front as 913A592. Order by the axle position you are working on.
