SOA on an early Bronco is a serious fabrication project — not a bolt-on lift. Done right it yields 8–10" of lift and 37–40" tire clearance with excellent articulation, but it touches springs, driveshafts, steering, and brakes, and it demands welding skills and a real shop. The result is a capable dedicated trail rig, not a comfortable street truck.
Spring over axle moves the leaf springs from below the axle housing to above it, using the full spring arch as lift rather than losing it under the axle. On an early Bronco with roughly 4.5" of spring arch, SOA yields about 8–10" of lift depending on spring selection. That's a lot of height from re-mounting parts you already own — but every system the suspension touches has to be corrected to make it safe and drivable. If 8–10" is more than you need, a bolt-in 4" lift gets you 35s with far less work.
The factory spring perches sit under the axle. SOA relocates them to the top of the housing, which means cutting off the old perches and welding new perch pads to the top of each axle tube. This is precision work — the perch centerline must align with the axle centerline, and the pinion angle is set here, so getting it wrong cascades into driveline vibration. This is the weld that the whole build rides on; if you're not confident in structural welding, this is the step to hand to a fab shop.
SOA changes the front shackle geometry. Some builders run a shackle reversal kit; others extend or re-locate the factory mount. Each approach has handling tradeoffs, and the goal is to keep the spring operating angle and caster sane so the truck tracks straight. Plan the front-end geometry as a package with the steering correction below, not as an afterthought.
SOA dramatically increases driveshaft angles. A custom front driveshaft (Tom Woods, Dynatrac) is mandatory. At the rear, the transfer case output angle changes enough to require a slip yoke eliminator on the Dana 20 plus a CV-style rear driveshaft — the same combination covered in Slip Yoke Eliminator and CV Driveshaft, here treated as non-optional rather than a lift-dependent upgrade. Measure pinion angle at ride height on the ground before ordering shafts.
With the axle dropped well below the frame, the drag link and tie rod now sit at a steep angle, which causes severe bump steer if left uncorrected. A dropped pitman arm or a high-steer kit restores the steering geometry. Pair it with a stout steering box and brace — see Steering Box Upgrade — because the leverage from 37s magnifies any slop in a tired factory box.
All brake lines must be custom-fabricated or extended to reach the dropped axle through its full travel. This is safety-critical — a brake line pulled tight at full droop will tear, so there are no shortcuts here. Factory shock mounts also end up at the wrong height and angle and have to be cut off and re-welded for long-travel shocks. Extended bump stops are required to keep the tire out of the body and the shock off its internal stops at full compression.
The recurring SOA failures are all geometry: pinion angle set wrong at the perch weld (chronic vibration), steering left uncorrected (dangerous bump steer), and brake lines built to static length instead of full-droop length. Mock up the full suspension cycle — stuff and droop each corner — before final-welding anything. And be honest about use: an 8–10" SOA Bronco on 37s is a trail machine that drives differently on the highway, with a higher center of gravity and slower steering. If the truck still needs to be a daily driver, the milder lift is the better call.
Budget $2,500 if you fabricate and weld it yourself with quality components, $6,000+ for a shop-built SOA with premium shocks and high-steer. The hardware isn't the expensive part — the fabrication time and the correction of every connected system is.
| Part | Vendor | Est. price |
|---|---|---|
| Custom spring perch plates (fabricated) | Fabricated | ~$80 |
| Tom Woods custom front driveshaft | Tom Woods | ~$420 |
| SYE (slip yoke eliminator) for Dana 20 | Various | ~$280 |
| Long travel shocks (extended/bypass) | King / Fox | ~$900 |
| Extended brake lines (full set) | Custom | ~$150 |
| Extended bump stops | Various | ~$60 |
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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