Lock the rear first — it returns more climbing capability per dollar than anything else you can bolt to an early Bronco. Add a selectable front afterward for steep, off-camber ledges where an open front stalls the climb. Do the locker at the same time as a regear so you pay the precision setup labor once, and check your axle shaft spline count before you order anything, because a locker behind tired 28-spline shafts finds their limit fast. The companion locker options guide compares the types; this card is the build decision and the install.
There is a persistent piece of misinformation in the early Bronco world worth clearing up before you spend money, because it changes what parts you order:
Every early Bronco, 1966 through 1977, came from the factory with a Ford 9-inch rear axle. There is no factory Dana rear in these trucks. The Dana in an early Bronco is the front axle: a closed-knuckle Dana 30 from 1966 to 1971, and a closed-knuckle Dana 44 from mid-1971 through 1977. Both front axles use kingpins rather than ball joints, which is why front-end service on these trucks looks nothing like a modern solid-axle truck — see the closed-knuckle service guide.
Three practical consequences follow from that:
This is the single most useful thing to understand about locking an early Bronco, and it is specific to the Ford 9-inch.
The 9-inch uses a removable carrier — the ring gear, pinion, carrier bearings, and differential all live in a cast third member that unbolts from the front of the housing as a unit. The Dana front axle does not work this way; it is an integral-carrier design where all the setup happens inside the housing, on your back, under the truck.
That difference gives you an option nobody talks about often enough: buy or build a second third member. Instead of tearing down the axle in your truck, you acquire a spare 9-inch center section, have it set up on a bench with the locker and the gears you want, and then swap it in. The physical swap is a few hours — drain, unbolt the driveshaft, pull the axle shafts, unbolt ten nuts, slide the old one out, new gasket, slide the new one in.
What that buys you:
Do not extend that logic to the front. The Dana 30 or 44 front has to be set up in the housing, in the truck or on a stand.
Rear — automatic (Eaton Detroit Locker, Yukon Grizzly). Mechanical, no air line, no switch, and it locks whenever it is loaded. On a light, short-wheelbase truck it is very effective and quite noticeable: it ratchets and clicks in tight pavement turns and can push the rear around in the wet. On a Bronco that mostly wheels, this is a defensible and cheaper choice at roughly $450 to $700.
Rear — selectable air locker (ARB). Fully open until you flip the switch, so the truck drives and steers normally on the road and locks only when you want it. Costs more once you add the compressor: about $1,000 to $1,400 all-in for the locker, compressor, and plumbing. The right answer if the Bronco sees meaningful street miles.
Rear — limited slip (Auburn, Truetrac). The mild option for a street-biased truck. Adds traction without changing manners. Not enough for hard rock, but a real improvement over open at $400 to $600.
Front — selectable, and effectively only selectable. An automatic locker in the front of an early Bronco fights the steering, and on the many trucks still running a manual box or a modestly assisted conversion it makes low-speed maneuvering genuinely difficult. Run an ARB up front, and leave it open until you need it.
Wild Horses and the other early Bronco specialists stock ARB, Yukon, Eaton, and Auburn units for both the 9-inch rear and the Dana fronts, so availability is not the constraint — the constraint is getting the spline count and the carrier series right.
This is precision work. The steps below are the shape of the job, not a substitute for the gear manufacturer's setup specifications.
A locker does not make weak shafts stronger — it makes them break. An open differential lets a spinning tire relieve load. A locker refuses to, and sends that torque into whichever shaft has grip. If you are running 28-spline small-bearing shafts, a locker plus 35s plus a V8 is the combination that snaps them. Budget 31-spline chromoly shafts with a large-bearing conversion, roughly $550 to $800 a pair, at the same time. On a semi-float 9-inch, a shaft that lets go outboard of the bearing can allow the wheel to leave the truck, so treat this as a safety item rather than a durability nicety.
Regear at the same time or accept paying twice. The carrier is out either way. Setup labor is the expensive part of both jobs, and combining them costs an extra $320 in gears and $130 in a master kit rather than another $500 to $800 in labor. See the regear guide.
Match ratios front to rear exactly. The Dana 20 transfer case splits drive evenly. A ratio mismatch binds the driveline and destroys parts.
Know when to hand it off. Ring and pinion setup is the most tolerance-critical work on the truck, and a pattern that looks close but is wrong produces a howl at 45 mph and a failed gear set at 8,000 miles. If you have not set up a third member before, the bench-swap route on the rear lets you buy the expertise without buying the tools.
A realistic rear-only build — automatic locker, gears, master kit, and shop setup — lands around $1,400 to $1,900. Adding a selectable front later brings the pair to roughly $2,800 to $3,600. Sequence it as rear locker and gears first, shafts with or immediately after, selectable front last. That order puts the capability on the truck in the sequence you will actually notice it.
| Part | Vendor | Est. price |
|---|---|---|
| Rear locker, Ford 9-inch (spline count must match your shafts) | ARB Air Locker / Eaton Detroit Locker / Yukon Grizzly / Auburn | ~$700 |
| Front locker, Dana 30 or Dana 44 (selectable recommended) | ARB Air Locker / Yukon Zip | ~$800 |
| Carrier bearing and master setup kit (per axle) | Yukon / Wild Horses 4x4 / Timken | ~$130 |
| Air compressor and locker plumbing kit (selectable only) | ARB CKSA12 / ARB CKMA12 | ~$320 |
| Spare Ford 9-inch third member, prebuilt with locker and gears | Currie / Wild Horses 4x4 / local axle shop | ~$1900 |
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.
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