Eaton Detroit Truetrac Differential 27 Spline 1.16in Axle Shaft Dia 3.54 & Down Ratio Front Dana 30
Plenty of Jeeps still run their factory 3.07, 3.21 or 3.55 gears, and owners of those trucks often want better front traction in snow, mud and on loose climbs without the clicking and steering fight of a front locker. The Eaton Detroit Truetrac 912A584 is the helical gear limited slip for the 27-spline Dana 30 front axle with 3.54 and numerically lower ratios, with 1.16 in. inner axle shafts. It fits the low-ratio Dana 30 found under CJ, Cherokee XJ, Grand Cherokee ZJ, Wrangler YJ and TJ, and non-Rubicon JK models.
An open Dana 30 sends equal torque to both front wheels, so when one tire loses grip the other gets almost nothing. The Truetrac uses parallel-axis helical pinions that mesh with each other and with the side gears. When one wheel starts to spin, the gear thrust loads the pinions against the case, and that friction biases torque toward the tire with more grip. There are no clutch plates, springs or switches, so nothing wears out the way a clutch-type posi does and there is nothing to engage. On the road it behaves like an open differential, which is why Eaton notes the torque transfer goes largely unnoticed by the driver even in a steering axle. The trade-off: if one tire is completely in the air with zero load, a Truetrac can act like an open diff. A light touch on the brake while applying throttle adds resistance and brings the bias back.
Check the ratio first. Dana 30 carriers come in two sizes, and this one is for 3.54 and numerically lower gears, which covers factory 3.07, 3.21 and 3.55 axles. If you have 3.73 or deeper gears, or plan to regear for bigger tires, order the Truetrac 912A585 for 3.73-and-up Dana 30s instead. Our carrier break guide explains the split. Then confirm 27-spline shafts and a Dana 30 rather than a Dana 44 front. If you are choosing between a Truetrac and a locker, Detroit Locker vs Truetrac lays out the driving difference, and the Truetrac buyers guide lists the other Eaton part numbers by axle.
Factory gear ratios changed by engine, transmission and trim, and many of these Jeeps have been regeared since, so the ratio on the axle tag or ring gear is what decides fitment, not the year. Send us your year, VIN and axle tag reading if you want us to check before it ships. Other carriers and front axle parts are in our hard parts collection.
Most Dana 30 owners never notice the Truetrac on pavement. In 4WD you will feel a little more pull through the steering wheel on throttle, which fades as soon as you ease off. If you also need maximum rock-crawling bite later, the ELocker4 for 3.55-and-down Dana 30s fits the same carrier size.
| Brand | Eaton |
| Part number | 912A584 |
| Fits | Eaton Detroit Truetrac Differential 27 Spline 1.16in Axle Shaft Dia 3.54 & Down Ratio Front Dana 30 |
| Type | Differentials |
| Condition | New |
| Ships | Same business day (in stock), from the USA |
| Warranty | 1-year |
No. It is the 3.54-and-down carrier. Gears of 3.73 and deeper need the 3.73-and-up Truetrac, Eaton part 912A585. Check the axle tag or count ring and pinion teeth before ordering.
Jeeps with a 27-spline Dana 30 front and a ratio of 3.54 or lower, including 1976-1986 CJ-7, 1981-1985 CJ-8, 1984-2001 Cherokee XJ, 1993-1998 Grand Cherokee ZJ, Wrangler YJ, TJ and LJ, and 2007-2018 non-Rubicon JK models.
No. The Truetrac is a helical gear design with no clutch plates, so it does not need limited slip additive. Use a quality 75W-90 GL-5 gear oil.
Far less than a locker. On the road it acts like an open differential. In 4WD you may feel some pull through the wheel under hard throttle, which is normal and goes away when you lift.
A helical limited slip needs some load on both tires to bias torque. With one tire fully unloaded it can act like an open diff. Lightly applying the brake while giving throttle usually brings the traction back.
New carrier bearings and races, ring gear bolts, inner axle seals and a cover gasket. A Dana 30 front master bearing or overhaul kit covers the bearings and seals.
