Eaton Detroit Truetrac Differential 35 Spline 1.50in Axle Shaft Diameter 4.10 & Down Ratio...

The Eaton Detroit Truetrac 915A387 is a gear-driven limited-slip for the front Dana 60 with 35-spline, 1.50 in. inner axle shafts and ring and pinion ratios of 4.10 and numerically lower. It is the carrier people search for when a Ford Super Duty, an older Dodge W-series or a GM K30 in four-wheel drive keeps losing a front tire to the open differential, and they want more front pull without the heavy steering and tire scrub a full locker brings. Because it behaves like an open differential until a tire slips, it is one of the easiest front traction upgrades to live with on a truck that also plows, tows or sees the highway with the hubs locked.

What the Truetrac does in a front Dana 60

The Truetrac uses helical pinion gears that sit in pockets in the case and mesh with two helical side gears. Under normal drive the gears rotate freely, so the front end steers and turns like it has an open carrier. When one front tire starts to spin, gear separating forces push the pinions into their pockets and the side gears against the case, creating the friction that biases torque toward the tire with grip. There are no clutch plates to wear, so the unit does not lose its bias over time the way a worn clutch-type limited-slip does. In a front axle that is a big deal: you get extra bite in mud and snow, but the steering stays light because the axle is not locked solid.

Symptoms that lead people to this carrier

• In 4WD the truck stalls on a slick climb with one front tire spinning and the other doing nothing.
• The plow truck digs a hole with one front tire in heavy wet snow.
• A front full locker made the steering too heavy or caused hopping in tight turns, and the owner wants something milder.
• Broken spider gears or a cracked cross shaft found while servicing hubs, U-joints or carrier bearings, three of the front Dana 60's common wear points.

How to confirm what your axle needs

Count the splines on an inner axle shaft and read the ratio from the axle tag; this carrier needs both to be right. Our carrier break guide explains why ratio decides the case, and the Truetrac buyers guide by axle and spline sorts the part numbers. For hub, ball joint and bearing problems to fix while the axle is apart, see Dana 60 front axle problems.

Fitment

Eaton's application list for 915A387 is front-axle only: 1977-1987 GM one-ton trucks, vans and cab-and-chassis with the Dana 60 HD, 1975-1991 GM three-quarter-ton trucks, 1971-1993 Chrysler and Dodge half-ton models, 1976-2000 Dodge and Ram three-quarter and one-ton trucks, and 1974-2020 and 1979-2020 Ford one-ton and three-quarter-ton trucks and vans with the front Dana 60, all with 4.10-and-down gearing. The Dana 60 carrier break sits between 4.10 and 4.56, so a 4.56 or deeper gear set needs the Truetrac Dana 60 35-spline 4.56-up. Many front Dana 60s use 30-spline inner shafts, so count before you order, and send us your year, axle tag and VIN if you want us to check. If you want both front tires locked, the Detroit Locker Dana 60 35-spline 4.10-down covers the same carrier break.

Install notes

Pull the hubs and inner axle shafts first, then mark the bearing caps. Spreading the housing with a Dana 60 housing spreader makes removing and setting the carrier much easier without overstretching the case. Transfer the ring gear with clean threads and new or thread-locked bolts, press on new carrier bearings, and recheck backlash and pattern since a new case can change shim needs; the Dana 60 master install kit includes bearings, shims and seals. Eaton's Truetrac lubrication guidance calls for a quality petroleum GL-5 gear oil and no friction modifier. Inspect inner axle seals and U-joints before the shafts go back in.

Is 915A387 for the front or rear Dana 60?

Eaton lists every application for 915A387 as a front axle. Rear Dana 60 Truetrac units use different part numbers.

Can I run 4.56 or 4.88 gears with it?

No. It is the 4.10-and-down case. Deeper gears are thicker and need the 4.56-and-up Dana 60 Truetrac.

Will a front Truetrac make my truck hard to steer?

Much less than a locker. It acts like an open differential until a tire slips, so steering effort in 4WD stays close to stock.

Does it need friction modifier or synthetic oil?

No friction modifier. Eaton recommends a quality petroleum-mineral GL-5 gear oil for the Truetrac.

My Dana 60 has 30-spline shafts. Will this fit?

No. This carrier is for 35-spline, 1.50 in. shafts. A 30-spline axle needs a 30-spline carrier or 35-spline inner shafts.

What should I replace while the axle is apart?

Carrier bearings, inner axle seals and any loose U-joints. On older trucks check ball joints or kingpins and wheel bearings too.