Flipping the rear leaf springs to sit on top of the axle (instead of under it) yields ~5.5" of cheap lift but requires significant fabrication and geometry fixes.
Spring-Over-Axle (SOA) means the rear leaf springs sit ON TOP of the axle housing rather than UNDER it. Stock XJs are spring-under; the SOA conversion gives roughly 5.5" of additional lift (axle drops by spring pack thickness, ~5.5") for the cost of welding new spring perches and addressing the geometry. The result is a long-travel rear with great articulation.
The conversion requires: cutting off the stock perches, welding new spring perches on top of the axle (positioned for correct pinion angle), longer rear shocks (or relocated mounts), longer rear brake line, addressing pinion angle (typically with degree shims on the new perches), and addressing axle wrap. Axle wrap is the biggest gotcha — the axle now sits above the springs, and under acceleration the axle wants to rotate forward, causing violent wheel hop. Fixes include anti-wrap bars, a traction bar, or moving to a 4-link with coils.
SOA is most common on builds going to 35"+ tires where short-arm and most long-arm kits run out of lift. It's labor-intensive and welding-heavy but the cost of materials is low (~$300 for perches, shims, longer u-bolts, shocks). Often combined with a front coil-over conversion or a Ford 8.8/Dana 44 rear axle swap (the swap and SOA happen together).
NAXJA's SOA writeups warn that without addressing axle wrap and pinion angle, an SOA XJ is unsafe at highway speeds. Done right, it's a beloved budget option for serious trail rigs.
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| Part | Vendor | Est. price |
|---|---|---|
| SOA perch kit | Ruff Stuff / Iron Rock | ~$80 |
| Longer rear shocks (~14" travel) | Bilstein / Fox | ~$200 |
| Anti-wrap bar kit | IRO / Clayton | ~$250 |
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.