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Both of these come out of the same Eaton box, both say Detroit on the label, and people mix them up all the time. They are completely different animals. The Detroit Locker is a full automatic locker: both axle shafts are locked together under power, and one side ratchets free only when you lift off and turn. The Detroit Truetrac is a helical gear limited slip: no clutches, no ratcheting, it just biases torque toward the wheel with grip until one tire is completely unloaded. Pick the wrong one and you will either hate driving the truck to work or wonder why you paid for traction you never get.
The Short Version
| Detroit Locker | Detroit Truetrac | |
|---|---|---|
| Type | Automatic mechanical locker | Helical gear limited slip (torque biasing) |
| Locks 100% | Yes, any time torque is applied | No, biases roughly 2.5 to 3 times the torque to the grippy side |
| Wheel in the air | Still pulls the other wheel | Acts like an open diff unless you drag the brakes |
| Street manners | Clicks, bangs, pushes in turns, can snap on throttle mid-corner | Feels like an open diff. Quiet, smooth |
| Front axle use | Only for dedicated off-road rigs, steering suffers badly | Fine, light steering pull under throttle |
| Fluid | Plain gear oil, no additive | Plain gear oil, no additive |
| Wear parts | Springs and driven clutches, very durable | Essentially none |
How a Detroit Locker Actually Works
Inside the case is a spider assembly with dog teeth, and a driven clutch on each side gear spring-loaded into it. Under power, both driven clutches are engaged and both axles turn at the same speed no matter what the traction is. In a turn, when you are off the throttle or close to it, the outside wheel needs to spin faster. A cam and holdout ring let that outside driven clutch climb up and ratchet over the teeth. That ratchet is the click you hear in parking lots.
The problem is the word "off the throttle." Roll into the gas halfway through a turn on a wet road and the outside clutch slams back into lock. The truck goes straight, or the rear steps out. In a short-wheelbase Jeep or a light rear-end car, that is the single biggest complaint. On a heavy 3/4-ton that tows, you barely notice it. That is why the Locker is common in 14-bolt and Dana 60/70 rears and a love-it-or-hate-it part in half-ton and smaller axles.
Two other quirks: tires wear faster on the rear, especially on dual-purpose rigs that see a lot of pavement. And if you run mismatched tire diameters, side to side, the Locker will make you feel every bit of it.
How a Truetrac Actually Works
The Truetrac uses parallel-axis helical pinion gears in pockets in the case. When one wheel tries to spin faster than the other, the gear separating forces push the pinions against the walls of their pockets and the side gears against the case. That friction resists the speed difference and sends more torque to the slower wheel. The bias ratio is roughly 2.5:1 to 3:1, meaning the wheel with grip can get up to about three times what the slipping wheel is putting down.
That is the catch. If the slipping wheel is putting down zero, three times zero is zero. Lift a tire off the ground on a rock or in a ditch crossing and the Truetrac spins it like an open carrier. The fix every Truetrac owner learns: lightly drag the brakes with your left foot. That gives the light wheel something to push against and the bias kicks in. It works well, but it is a technique, not automatic traction.
On the street it is the best traction upgrade you can put in a daily driver. No chatter, no friction modifier, no clutch packs to wear out, and it does not fight you in turns. Snow, wet boat ramps, gravel drives and towing are exactly where it shines.
Which One for Your Truck
Daily driver that tows or sees snow: Truetrac
Half-ton GM, Ford 8.8 and 9.75, Ram 9.25, Jeep Dana 44 rear on a street-driven Wrangler. If it spends 90 percent of its life on pavement, buy the Truetrac and never think about it again. We carry the Truetrac for Ford 8.8, 33-spline ($803.99), the Truetrac for GM 1500 9.5 and 9.76 inch, 33-spline ($830.99), the Truetrac for Ram 9.25, 31-spline ($729.99), the Truetrac for GM 8.5 10-bolt, 30-spline, 3.73 and up ($746.99) and the Truetrac for JK Dana 44 rear, 32-spline ($1,044.99).
Work truck, plow truck, dedicated trail rig: Locker
On a 2500 or 3500 with a 14-bolt or AAM 11.5, the rear Locker is close to invisible because the truck is so heavy and long. It is also nearly unkillable. For a GM or Ram 10.5 14-bolt, the Detroit Locker for 10.5 inch, 30-spline ($713.99) is one of the best values in our axle section. On a trail rig with lots of articulation, the Locker gives you traction with a wheel in the air without asking you to do anything.
Want both: selectable
If you want open-diff manners on the street and 100 percent lock on the trail, an air or electric selectable is the third answer, at more money and more things to fail. Our open vs limited slip vs locker guide walks through those trade-offs.
Ordering the Right Carrier
Both units are sold by axle, spline count and ratio range, and getting any of those wrong is the number one return reason. Four things to confirm before you order:
- Axle model and ring gear size. Read the axle tag or RPO code. Our guide to finding your axle code and gear ratio covers GM, Ford and Ram.
- Spline count. Count the splines on the axle shaft or look up the build. Many half-ton axles changed spline count mid-generation.
- Carrier break. Many axles use one case for numerically low ratios and a thicker-flange case for 3.73 or 3.92 and up. If you are regearing, order the carrier for the new ratio.
- C-clip or not. C-clip axles need the right cross shaft arrangement in the carrier; most Truetracs and Lockers handle it, but check the listing notes.
Install Notes From the Bench
Either swap is a carrier change, which means new carrier bearings and a fresh backlash and preload check. Reusing tired carrier bearings to save $60 is how a new $800 diff turns into a whining axle. A Ford 8.8 master bearing kit ($162.99) or the equivalent for your axle covers it, and a dial indicator and magnetic base ($95.99) is non-negotiable for checking backlash. Our backlash and pinion depth setup guide has the numbers.
Fill with straight GL-5 gear oil. Neither unit needs friction modifier. If you just pulled a clutch-type posi, flush the old oil out completely so the leftover modifier does not end up in the new carrier.
What It Costs
| Job | Parts | Shop install (rough) |
|---|---|---|
| Truetrac, half-ton rear | About $730-$1,050 plus $150-$250 bearings | About $400-$700 labor |
| Detroit Locker, HD rear | About $700-$1,100 plus bearings | About $450-$800 labor |
| Carrier swap during a regear | Same diff price | Adds little labor, the axle is already apart |
If the noise or slip you are chasing is actually in the driveline ahead of the axle, CoreTransmissionParts.com carries the transmission and transfer case rebuild parts.
Pick Your Detroit
Truetrac for the daily driver, Locker for the work truck and the trail rig. Order by axle, spline count and ratio.
Shop Truetrac → Shop Detroit LockerFAQ
Is a Detroit Truetrac a locker?
No. The Truetrac is a helical gear limited slip that biases torque toward the wheel with more grip. It never fully locks, and with one wheel completely off the ground it behaves like an open differential unless you lightly apply the brakes.
Can you daily drive a Detroit Locker?
Yes, but you will hear clicking in turns and feel the rear push or snap if you get on the throttle mid-corner, especially in short, light vehicles or on wet roads. On heavy 3/4-ton and 1-ton trucks it is barely noticeable.
Does a Truetrac or Detroit Locker need friction modifier?
No. Neither uses clutch packs, so they run on plain GL-5 gear oil. Flush out any old oil that contained limited-slip additive when you install one.
Should I put a Detroit Locker in the front axle?
Only on a dedicated off-road vehicle. A full-time front locker makes steering heavy and the truck plows in turns whenever 4WD is engaged. A Truetrac is a much better front axle choice for a vehicle that also sees street miles.