Replacement of the leaf spring U-bolt kit on the rear suspension, securing the axle housing to the leaf springs with new U-bolts, plates, and hardware.

Warnings

Tools required

Parts

• Leaf spring U-bolt kit (includes U-bolts, nuts, and axle plate) × 1 — Use OEM specification or heavy-duty aftermarket equivalent
• Anti-seize compound × 1 — High-temperature rated

Preparation

1. Park vehicle on level, solid surface and engage parking brake
2. Chock front wheels securely on both sides
3. Loosen rear wheel lug nuts while vehicle is on ground (do not remove)
4. Raise rear of vehicle with floor jack at approved lift points
5. Support frame rails with jack stands rated for vehicle weight, ensuring axle can move independently
6. Remove rear wheels completely
7. Apply penetrating oil to existing U-bolt nuts if corrosion is present, allow 10-15 minutes to penetrate

Procedure

1. 1

   Support the rear axle assembly
   Position a floor jack or transmission jack under the rear axle differential housing to support the axle weight. Raise jack until it just contacts the axle but does not lift it. The axle must remain supported throughout U-bolt removal to prevent it from dropping away from the leaf springs.
2. 2

   Remove existing U-bolt nuts
   Using a socket and breaker bar, remove the four nuts securing the U-bolts (two U-bolts per side, four nuts total per axle end). Work on one side of the vehicle at a time. Remove nuts in a criss-cross pattern to evenly release tension. Keep track of any washers or hardware for reference.
   ⚠As you loosen the final nuts, the axle may shift slightly. Ensure the jack is supporting the axle securely.
3. 3

   Remove old U-bolts and axle plate
   Once nuts are removed, pull the U-bolts downward out of the axle plate and spring perch. Remove the lower axle plate from beneath the leaf spring. Inspect the spring perch on top of the axle for damage or excessive wear. If working on both sides, complete one side fully before moving to the opposite side.
4. 4

   Clean mounting surfaces
   Use a wire brush to clean the spring perch on top of the axle housing and the mating surface on the bottom of the leaf spring. Remove all rust, dirt, and old thread compound. Clean the U-bolt hole threads in the axle plate if reusing the plate, or prepare new plate from kit.
5. 5

   Inspect leaf springs and perch alignment
   Visually inspect leaf springs for cracks, broken leaves, or separation between leaves. Check that the spring center bolt is tight and the spring is properly seated in the axle perch. Ensure the axle is centered on the leaf spring before proceeding. Adjust axle position on jack if needed.
   ⚠If leaf springs show any cracks or damage, they must be replaced before continuing. Do not attempt to repair damaged springs.
6. 6

   Position new axle plate and U-bolts
   Place the new lower axle plate beneath the leaf spring, aligning it with the spring center. Insert the new U-bolts from above, threading them down through the spring perch, around the axle housing, through the leaf spring, and through the holes in the lower plate. Apply a light coat of anti-seize compound to the U-bolt threads.
7. 7

   Install U-bolt nuts hand-tight
   Thread all four nuts onto the U-bolt ends by hand. Tighten nuts evenly in a criss-cross pattern (alternating diagonal corners) until all nuts are snug but not torqued. Ensure the axle plate is seated flat against the bottom of the leaf spring and the U-bolts are perpendicular to the plate.
8. 8

   Torque U-bolt nuts to specification
   Using a calibrated torque wrench, tighten the U-bolt nuts in multiple stages using a criss-cross pattern. First pass: torque to 50% of final specification. Second pass: torque to 75% of final specification. Final pass: torque all nuts to the manufacturer's specified torque for leaf spring U-bolts. For 2021-2024 F-150, this is typically 148-203 Nm (109-150 lb-ft) depending on axle configuration - consult the U-bolt kit instructions or service manual for exact specification. Make at least two complete sequences at final torque to ensure even clamping.
   ⚠Uneven torquing can cause axle misalignment and premature wear. Always use criss-cross tightening pattern.
9. 9

   Repeat for opposite side
   If only one side was completed, repeat steps 2 through 8 for the opposite side of the vehicle. Ensure both sides are torqued to the same specification for balanced clamping force.
10. 10

    Remove axle support and reinstall wheels
    Carefully lower and remove the jack from under the rear axle. Reinstall the rear wheels, threading lug nuts by hand first. Lower the vehicle until wheels contact the ground but vehicle weight is not fully on wheels. Torque lug nuts to specification in a star pattern.
    Torque spec

    Wheel Lug Nuts156 Nm (115 lb-ft)
11. 11

    Lower vehicle and perform final checks
    Fully lower the vehicle to the ground and remove jack stands. With vehicle weight on suspension, re-check U-bolt nut torque on both sides to verify proper clamping force under load. Rock the vehicle side-to-side to settle the suspension.

Reassembly

1. After initial test drive (50-100 miles), re-torque U-bolt nuts to specification as they may settle slightly
2. Check for any unusual noises or handling changes that could indicate improper installation
3. Dispose of old U-bolts properly - do not reuse stretched fasteners

Verification

• Verify all U-bolt nuts are torqued to specification using torque wrench
• Visually confirm axle plates are seated flat against leaf springs with no gaps
• Check that U-bolts are perpendicular to mounting plates, not cocked at an angle
• Test drive vehicle at low speed and verify no clunking, banging, or unusual rear suspension noises
• Inspect for proper rear axle alignment - vehicle should track straight with no pulling
• Re-check torque after 50-100 miles of driving as part of break-in procedure

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