If you wheel an early Bronco on anything past a graded fire road, an open differential is the first thing holding you back. A selectable locker in the rear delivers the biggest single traction gain you can buy. Front locker comes next, and it should be selectable so the truck still steers predictably on the street.
An open differential sends power to the wheel with the least grip. Lift one tire off a rock and that tire spins while the planted one does nothing. Lockers force both wheels on an axle to turn together, so the tire with grip gets power.
There are three honest categories, and the right pick depends on how the truck gets used.
A selectable locker stays fully open until you flip a switch, then locks 100%. On the street it behaves like a stock open diff — no tire chirp in turns, no driveline bind. On the trail you lock it the instant you need it.
This is the pick for a truck that drives to the trail under its own power. The ARB Air Locker is the long-standing choice for early Broncos and needs an air source — either the ARB compressor or an existing onboard air system. Plan for the compressor cost in your budget, plus running an air line and a switch.
Tradeoff: more parts, more install time, and a small failure surface (air lines, seals). The payoff is street manners no other locker matches.
Automatic lockers are locked by default and "unlock" by ratcheting one wheel ahead of the other in turns. The full-case Detroit Locker is durable and a long-time favorite for the Ford 9-inch rear. Drop-in units like the Lock-Right and Aussie Locker reuse your existing carrier, which keeps cost and install time down.
The catch is street behavior. Automatic lockers bang, click, and can push the rear end wide in tight low-speed turns, especially in the wet. In a light early Bronco that behavior is noticeable. Many owners run an automatic in the rear and accept the manners; fewer want one in the front, because it affects steering.
A limited-slip (clutch-type like a Trac-Lok, or gear-type like a Truetrac) biases torque toward the wheel with grip without fully locking. It is the mildest option — good for a mostly-street truck that sees occasional dirt, weak for hard articulation where a tire leaves the ground entirely. Truetrac gear units are maintenance-free; clutch units wear and eventually need a rebuild.
Most early Bronco builds land here: automatic or selectable locker in the Ford 9-inch rear first, then a selectable ARB in the Dana 44 front when budget allows. Lock the rear and you solve the majority of traction problems. Add the front and the truck climbs almost anything its tires can reach.
You probably don't need a front locker if you mostly run graded trails and fire roads — a rear locker alone covers that. Save the front money for tires and recovery gear instead.
Installing a carrier — locker or otherwise — disturbs the ring-and-pinion setup. Drop-in lockers that reuse the factory carrier preserve your existing backlash and pinion depth, which is why they install faster. Full-case lockers (ARB, Detroit) replace the carrier entirely, so the gears must be re-shimmed and the backlash and pattern verified with a dial indicator.
If you have not set up a differential before, this is the step to hand to a shop. A locker installed with the wrong backlash will howl, run hot, and fail early. Budget $250–$400 for shop setup labor if you supply the parts.
Always confirm spline count and carrier break before ordering — Dana 44 fronts and Ford 9-inch rears come in more than one spline configuration depending on the prior build history of the truck.
| Part | Vendor | Est. price |
|---|---|---|
| ARB Air Locker (Dana 44 front, 30-spline) | ARB | ~$1100 |
| Detroit Locker (Ford 9-inch rear, 31-spline) | Eaton | ~$650 |
| Lock-Right / Aussie Locker (drop-in) | Powertrax | ~$350 |
| ARB compressor kit | ARB | ~$320 |
Written and maintained by an AZ wheeler and driveway wrencher. Always cross-reference your factory service manual — modifications affect vehicle safety and warranty. Work at your own risk.