Eaton Detroit Truetrac Differential 35 Spline 1.50in Axle Shaft Dia 4.56 & Up Ratio Rear...

One-ton Dana 60 rears, the full-float axles under Dodge W350s, older Ford and GM one-tons and plenty of built crawler and tow axles, usually carry 35-spline, 1.50 inch shafts. Once those trucks are regeared to 4.56, 4.88 or 5.13 for big tires or a heavy camper, the original carrier no longer fits the gears. The Eaton Detroit Truetrac 915A386 is the helical limited slip for that exact combination: a Dana 60 rear with 35-spline shafts and 4.56-and-up gears.

What the Truetrac does in a deep-geared Dana 60

A Truetrac has no clutches. Sets of helical pinions ride in pockets in the case and mesh with helical side gears. Driving straight or turning on good pavement, it behaves like an open differential and stays silent. When one tire begins to spin, the gear separating forces press the pinions into their pockets, the friction rises, and torque moves to the tire with more grip until the spin slows or stops. Eaton lists automatic engagement, forward and reverse operation, and no maintenance. With deep gears and large tires, the axle sees more torque at the wheel, and a unit with nothing to burn up or slip is a good match for towing and loaded trail use.

Symptoms that point to this unit

• One-tire spin after a regear to 4.56 or deeper, on ice, mud or a loose trailhead
• A worn Powr-Lok or Trac-Lok that slips and chatters, now too weak for bigger tires
• A cracked or worn open case or spider gears found during a gear swap
• Rear axle rebuild where you want traction without the clicking of an automatic locker

How to confirm before ordering

Check three things. First, that the axle is a Dana 60 and not a Dana 70 or GM 14-bolt; the tag and a 10-bolt cover help. Second, the spline count: pull a shaft and count 35. Third, the ratio. Dana 60 gears from 4.56 down use a different carrier than 4.10-and-lower gears, so the gears you will run decide the case. If you are keeping a thick 4.88 set made for the smaller carrier, this is not the unit. Our Dana 60 ring and pinion buyer's guide and the carrier break explainer walk through it.

Fitment

From the listing and Revolution's spec block: Dana 60 rear, 35-spline axles with a 1.50 inch shaft diameter, 4.56-and-up carrier break. There is no vehicle-by-year list because Dana 60 rears were used across many makes, so match the axle tag, spline count and ratio, or send us year and VIN. If your gears are 4.10 or lower, order the 35-spline 4.10-down Truetrac. Want a selectable unit instead? See the ELocker4 Dana 60 35-spline 4.56-up. All axle parts are in our hard parts collection.

Install notes

• Set up the new gears and this carrier together. Replace pinion and carrier bearings with a kit such as the Revolution Dana 60 master install kit.
• Carrier preload comes from shims and housing stretch. A Dana 60 housing spreader keeps the bearing races from being hammered in or out.
• Use new ring gear bolts with thread locker and verify backlash and a centered pattern; deep ratios are less forgiving of pinion depth errors. Our backlash and pinion depth guide covers the marks.
• If shafts are twisted from big tires, a Yukon 1541H alloy 35-spline rear axle is the matching upgrade. Measure length first.
• Fill with GL-5 gear oil and leave out friction modifier; Eaton states it reduces Truetrac performance. Follow the ring and pinion break-in procedure before towing.

Can I use 915A386 with my factory 4.10 gears?

No. It is the 4.56-and-up carrier. A Dana 60 with 4.10 or lower gears, or a thick deep-ratio set built for the smaller carrier, needs the 4.10-and-down Truetrac.

Does it fit a Dana 70 or GM 14-bolt?

No. It is machined for the Dana 60 ring gear and bearings only. Dana 70 and 14-bolt axles use their own Truetrac part numbers.

Is a Truetrac good with a tire in the air?

With one tire completely unloaded there is little resistance to multiply. A light brake drag with your left foot helps. For frequent three-wheeling, a selectable locker fits better.

What oil does it need?

A quality GL-5 gear oil, mineral or synthetic per the axle maker. Eaton says not to add friction modifier.

Should I regear and install the Truetrac at the same time?

Yes, if you are going to 4.56 or deeper. The carrier has to change with the ratio anyway, so set the gears up on the new case with new bearings in one job.