The Ford 9-inch is the rear axle most serious early Bronco builds end up running. It is stronger than the factory rear, has a removable third member that makes gear and locker changes far less painful, and the aftermarket support is endless. If you are regearing and adding a locker anyway, swapping to a 9-inch first is often the better spend.
The early Bronco shipped with a Ford 9-inch rear from the factory in many configurations, but axle width, gear ratio, and spline count vary, and decades of swaps mean you cannot assume what is under any given truck. A purpose-built 9-inch — whether a salvage Explorer housing narrowed and re-perched, or a new aftermarket housing from Currie or Dynatrac — gives you a known starting point.
The defining feature is the dropout third member. The entire ring-and-pinion, carrier, and locker live in a removable center section that bolts to the front of the housing. You can set up a spare third member on the bench, then swap gear ratios or add a locker in an afternoon without disturbing the axle shafts or brakes. No other common axle makes drivetrain changes this approachable.
Strength scales with build. A 28-spline 9-inch is adequate for stock-ish tires; 31-spline handles 35s and moderate wheeling; 35-spline alloy shafts in a nodular case carry 37s and abuse. Match the spline count to your tire size and how hard you wheel.
This is a fabrication-adjacent job, not a bolt-in. The work breaks down as:
1. **Width and perch location.** The new housing must match your wheel mounting width and your leaf spring spacing. A salvage housing usually needs to be narrowed and always needs new spring perches welded at the correct location and pinion angle.
2. **Pinion angle.** With the perches tacked, measure the driveline angle before final welding. Get this wrong and you will fight vibration or a worn U-joint for the life of the build.
3. **Brakes.** Plan a disc conversion at the same time. Doing brakes while the axle is out is far less work than revisiting it later, and a heavier, more capable rear deserves better stopping.
4. **Gears and traction.** Set the third member up with your target ratio and a locker before it goes in. See the gear ratio and locker guides for ratio selection by tire size.
Pinion angle and perch placement are where these builds go wrong. Measure twice, tack, verify on the ground at ride height, then weld. A driveline angle gauge is worth the small cost.
If you are buying a salvage Explorer 8.8 instead of a true 9-inch, understand the tradeoff: the 8.8 is cheaper and adequate for many builds, but it lacks the dropout serviceability that makes the 9-inch worth the premium. For a build that will see multiple gear or locker changes over its life, the 9-inch pays you back.
Budget $900 for a salvage-based build you assemble yourself, $3,500 for a new-housing build with premium internals and shop setup. This is a long-horizon upgrade — done once, it carries the truck through every future tire and gearing change.
| Part | Vendor | Est. price |
|---|---|---|
| Ford 9-inch housing (Explorer or aftermarket) | Salvage / Currie | ~$400 |
| New axle shafts (35-spline, alloy) | Yukon / Moser | ~$450 |
| Spring perches (weld-on) | Ruffstuff | ~$40 |
| Disc brake conversion kit | Various | ~$350 |
| Detroit Locker or Truetrac carrier | Eaton | ~$600 |
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.