Shop All Transmission Parts →
The Eaton Detroit Truetrac is the limited slip most people should buy and the one that gets ordered wrong most often. It is a helical gear differential: instead of a clutch pack fighting the spider gears, it uses sets of parallel helical pinions sitting in pockets in the case. When one tire starts to spin, the pinions thrust against the pocket walls and the friction that builds up sends more torque to the tire that still has grip. There are no clutches, no springs to fatigue, and no friction modifier to forget at the next fluid change.
That design is why it is popular on daily-driven trucks, tow rigs and street cars. It is quiet, it does not chatter in parking lots, and it is invisible to ABS and traction control. But the carrier is machined for one specific ring gear bolt pattern, one carrier bearing size, one spline count and, on many axles, one range of gear ratios. Get any of those wrong and the part goes back in the box.
Is a Truetrac the Right Diff for You?
| Use | Truetrac? | Why |
|---|---|---|
| Daily driver, snow, wet boat ramps | Yes | Smooth, automatic, no driver input, no clunks. |
| Towing and work trucks | Yes | Nothing to wear out under steady load, works with standard gear oil. |
| Street and strip | Yes | Puts both tires down without the bark and hop of a full locker. |
| Rock crawling, frequent three-wheeling | Usually no | With one tire fully in the air there is almost no resistance to multiply. A selectable locker fits that job better. |
The one-tire-in-the-air limitation is real, but there is a simple trick: drag the brake lightly with your left foot. That adds resistance at the spinning wheel and the helical gears multiply it back across to the wheel with traction. Off-roaders who mostly do trails, sand and mud live with it fine. If your truck spends weekends stuck on ledges, read our Detroit Locker vs Truetrac comparison and our open vs limited slip vs locker breakdown first.
The Four Things You Need Before You Order
1. The axle, by name, not by vehicle
"2016 F-150" is not enough. That truck could have an 8.8 or a 9.75 rear depending on engine and axle option. Pull the axle tag or read the door sticker axle code, then count the cover bolts and measure the ring gear if you have to. Our guide on finding your axle code and gear ratio walks through it.
2. Spline count
The case has to match your axle shafts. Ford 8.8 rears came in 28 and 31 spline, and the later trucks went to 34. GM 9.5 and 9.76 rears are 33 spline. Ram 9.25 is 31. Dana 44s run 30 or 32 depending on generation. If you are swapping in aftermarket shafts at the same time, order to the new shaft spline, not the old one.
3. Gear ratio and the carrier break
Many axles have a carrier break: numerically higher ratios use a smaller pinion and a ring gear that sits farther out, so the carrier flange is a different height. That is why several Truetrac listings say "3.73 and up" or "3.54 and down." Order for the ratio that will be in the axle after the job, especially if you are regearing at the same time. Our carrier break explainer covers which axles have one and where it falls.
4. Axle shaft diameter and C-clip vs full-float
Some cases are offered for different shaft diameters at the same spline count, and C-clip axles need a case with the right cross-shaft and clip window. Full-float rears like the 10.25 and 10.5 use a different case entirely.
Common Applications We Stock
| Axle / Vehicle | Spline | Notes |
|---|---|---|
| 2015-2023 F-150 rear | 34 | 3.31 and numerically higher ratios. |
| 2009-2023 F-150 4x4 front 8.8 | 31 | All ratios. A front Truetrac is a big upgrade for snow plowing and boat ramps. |
| GM 1500 9.5 / 9.76 rear | 33 | 3.42 and 3.73 trucks. Popular replacement for a worn G80. |
| Ram pickup 9.25 rear | 31 | Half-ton Ram rear axle. |
| Dana 44 M210 / M220 | 32 | Late-model Jeep front and rear axles. |
| 2020-2025 GM 2500HD 6.6 diesel | 31 | Diesel rear only; check the listing notes against your build. |
| Ford 10.25 / 10.5 full-float | 35 | Super Duty and older one-ton rears. |
Typical Truetrac pricing runs roughly $640 to $900 for half-ton and Jeep applications, and $1,000 to $1,300 for heavy-duty and full-float cases. If you do not see your axle in the table, browse our hard parts section or send us the axle tag info before you order.
What the Install Actually Takes
A Truetrac replaces the whole carrier. Your ring gear moves over to the new case, and the backlash and carrier bearing preload have to be set again. If you are not changing the ring and pinion, pinion depth stays where it is, which keeps this a lot simpler than a full regear.
- New carrier bearings and races. Pressing used bearings off a carrier usually damages them. Plan on a new set.
- New ring gear bolts. They are torque-to-spec fasteners and cheap insurance. Use thread locker on clean threads.
- Check backlash and the contact pattern. Do not assume the old shims will give the same result on a new case. Our backlash and pattern guide covers the process.
- Plain gear oil. No friction modifier is required. A conventional or synthetic 75W-90 or 75W-140 as your axle calls for is fine.
Shop labor for a carrier swap with no gear change is typically 3 to 5 hours. Combined with a regear the extra time is small, because the axle is already apart and the bearings are already being replaced, which is why most people install the Truetrac and new gears together.
Find Your Truetrac
Truetrac cases for Ford, GM, Ram, Dana and full-float axles, plus the bearing kits and gear sets to install them right. Ships fast from the USA.
Shop Hard Parts →FAQ
Does a Detroit Truetrac need friction modifier?
No. It has no clutch packs, so standard gear oil is all it needs. Adding friction modifier will not hurt it, but it does nothing.
Will a Truetrac work with ABS and traction control?
Yes. It biases torque smoothly and never locks the axle solid, so ABS, stability control and traction control work as designed.
Can I reuse my ring gear on a Truetrac?
Yes, as long as the case matches your ratio range and carrier break. Use new ring gear bolts and recheck backlash.
How long does a Truetrac last?
There are no wear clutches, so in normal service it usually outlasts the ring and pinion. Failures are rare and tend to come from abuse or low oil.