Leaf Spring Selection, Ride Height, Travel, and Bump Control

Design variables that matter

• Spring length — longer springs give better ride quality but need more frame real estate.
• Spring width — determines U-bolt kit and axle spring perch spacing.
• Rate & arch — matched to sprung weight and target ride height. Wrong rate = axle wrap or sagging.
• Shackle geometry — length and angle set wheel-rate progression through travel.
• Fixed-eye orientation — controls whether the axle moves forward or rearward under compression.

Axle wrap & anti-wrap

Leaf springs resist axle rotation, but under hard braking or throttle they can wrap S-shaped, pulling the pinion out of alignment. Options include stiffer springs, add-a-leafs, traction bars, or a wrap-restricting link — each with tradeoffs for articulation and ride quality.

Full-bump / full-droop mock-up procedure

1. Support the frame at target ride height on level ground.
2. Cycle the axle to full bump (spring flat / shock fully compressed). Check clearances everywhere: fenderwell, oil pan, exhaust, brake hose, ABS wire, tire to firewall.
3. Cycle to full droop (axle hanging on shocks, driveshaft, or straps — decide which is the limit). Recheck brake hose tension and driveshaft engagement.
4. Record travel numbers in the Measurement Workbook.

Shocks & bump control

• Shock extended and compressed lengths must match travel — a shock is not a droop limiter.
• Bump stops protect the shock, the spring eye, and the sheet metal — never delete them.
• Droop limiters (straps) protect the front driveshaft, brake hoses, and front spring eye.

Caster / pinion compromise

Solid axles couple caster angle to pinion angle. Correct caster for steering return and stability rotates the pinion; corrected steering pinion angle may fight your driveshaft. Design this compromise on paper before ordering shims or degree wedges.