Eaton Detroit Truetrac Differential 27 Spline 1.16in Axle Shaft Dia 3.73 & Up Ratio Front Dana 30
Regearing a Jeep for 33 or 35 in. tires usually means 4.10, 4.56 or 4.88 gears, and that moves the Dana 30 front onto the larger carrier break. The Eaton Detroit Truetrac 912A585 is the helical gear limited slip for that case: a 27-spline Dana 30 front with 1.16 in. inner shafts and a 3.73 or numerically higher ratio. It is for the Wrangler, Cherokee or Scout owner who wants the front axle to pull both tires in snow, mud and on ledges without the steering fight of a full-time locker in the front.
With an open front diff, the front tire with the least grip decides how much torque the whole axle can put down, and on a hill that usually means one tire spinning while the other does nothing. The Truetrac uses sets of helical pinion gears riding in pockets in the case. As soon as one side tries to spin faster, the separating thrust on those angled teeth loads the pinions against their pockets and against each other, and that friction sends more torque to the tire that is still biting. It is automatic, needs no air line or wiring, and with no clutch packs there is nothing to slip or wear thin over time. Eaton lists the 912A585 at 17.64 lb with a 7.2 in. ring gear size. Deeper gears multiply the torque that reaches the carrier, and helical bias delivers it progressively rather than slamming it into the shafts and U-joints.
Start with the gear ratio. Dana 30 carriers are split at 3.54 and 3.73, and this one only accepts 3.73 and numerically higher ring gears. If you have 3.07, 3.21 or 3.55 gears and are not regearing, the Truetrac 912A584 for 3.54 and down is the right unit. Our carrier break guide explains why the split exists. Next, check the housing. Eaton notes this Truetrac applies to non-axle-disconnect housings only, so if your Dana 30 has an axle disconnect, ask us before ordering. Last, confirm it is a Dana 30 and not a Dana 44 front; our Dana 30 vs Dana 44 guide shows how to tell them apart, and the Dana 30 problems guide covers noises to rule out first.
Jeep fronts changed between high-pinion, low-pinion and reverse-rotation versions over those years, and that matters for the ring and pinion you pair with it. Send us your year, VIN and axle tag if you want a check before it ships. More front axle parts are in our hard parts collection.
If you later want a front that locks solid on demand for rock crawling, the ELocker4 for 3.73-and-up Dana 30s uses the same carrier size.
| Brand | Eaton |
| Part number | 912A585 |
| Fits | Eaton Detroit Truetrac Differential 27 Spline 1.16in Axle Shaft Dia 3.73 & Up Ratio Front Dana 30 |
| Type | Differentials |
| Condition | New |
| Ships | Same business day (in stock), from the USA |
| Warranty | 1-year |
No. It is the 3.73-and-up carrier. Ratios of 3.54 and lower need the 3.54-and-down Truetrac, Eaton 912A584, unless you regear at the same time.
Yes, Eaton lists it for the 2007-2018 Wrangler JK front Dana 30 with 3.73 and up gears. Rubicon JKs use a Dana 44 front and need a different unit.
Eaton states this Truetrac applies to non-axle-disconnect housings only. If your front axle has a disconnect, contact us with your year and VIN before ordering.
No. The Truetrac uses helical gears, not clutches, so a quality 75W-90 GL-5 gear oil is all it needs.
On a part-time 4WD system in 2WD the front axle is not driven, so the Truetrac has no effect. In 4WD it behaves like an open diff until a tire slips, with some pull through the wheel under heavy throttle.
Carrier bearings and races, new ring gear bolts, inner axle seals and a cover gasket. If you are regearing, a ring and pinion with a master install kit covers nearly everything.
