Replace the rear leaf spring U-bolt kit on a 2015-2020 Ford F-150 5.0L V8, securing the axle to the leaf springs with new U-bolts, nuts, and plates.

Warnings

Tools required

Parts

• Leaf spring U-bolt kit (includes U-bolts, nuts, washers, and backing plate) × 1 — Use OEM Ford specification or quality aftermarket kit
• Anti-seize compound × 1 — Generic high-temperature anti-seize

Preparation

1. Park vehicle on level, solid ground and engage parking brake
2. Place wheel chocks in front of both front wheels
3. Loosen rear wheel lug nuts while vehicle is on ground, but do not remove
4. Raise rear of vehicle using floor jack at rear differential or frame rail jacking points
5. Support vehicle with jack stands under frame rails on both sides, ensuring stands are secure and level
6. Remove rear wheels completely
7. Spray penetrating oil on all U-bolt nuts and allow to soak for 10-15 minutes

Procedure

1. 1

   Support the rear axle
   Position a floor jack under the rear differential housing. Raise the jack until it just contacts the differential and takes a slight amount of weight, but does not lift the vehicle off the jack stands. The axle must be supported independently throughout this procedure to prevent it from dropping when U-bolts are removed.
2. 2

   Remove U-bolt nuts
   Using a 19mm or 21mm socket (verify size on your specific kit), remove the nuts from all four U-bolt legs on the side being serviced. Remove nuts in a crisscross pattern to release tension evenly. If nuts are seized, apply additional penetrating oil and use a breaker bar for extra leverage.
3. 3

   Remove old U-bolts and backing plate
   Once all nuts are removed, pull the U-bolts out from the spring seat. Remove the backing plate (also called spring plate or axle pad) from between the axle and leaf spring. Inspect the plate for damage or deformation. Note the orientation of the plate for reinstallation.
4. 4

   Clean mating surfaces
   Use a wire brush to clean the top of the leaf spring pad, bottom of the axle tube, and the spring seat area. Remove all rust, dirt, and old thread compound. Clean the U-bolt threads on the axle spring seat. Ensure surfaces are clean and flat for proper seating of new components.
5. 5

   Inspect leaf spring and components
   With the U-bolt removed, visually inspect the leaf spring for cracks, broken leaves, or separation. Check spring bushings at the front eye and rear shackle for wear or deterioration. Inspect the spring center bolt to ensure it is tight. Address any issues before proceeding with U-bolt installation.
6. 6

   Position new backing plate
   Place the new backing plate from the U-bolt kit between the axle tube and leaf spring in the correct orientation. The plate should sit centered on the spring pad. Ensure the axle is properly seated in the spring pad with the center bolt located in the axle seat dimple.
7. 7

   Install new U-bolts
   Insert the new U-bolts down through the spring seat holes and around the axle tube. Guide the U-bolt legs through the holes in the leaf spring. Apply a light coat of anti-seize compound to the U-bolt threads. Install new washers and nuts on all four U-bolt legs, threading them on by hand.
8. 8

   Tighten U-bolt nuts in sequence
   Using a torque wrench, tighten the U-bolt nuts in a crisscross pattern (front passenger, rear driver, front driver, rear passenger). First pass: torque to 30 lb-ft. Second pass: torque to 60 lb-ft. Third pass: torque to 90 lb-ft. Final pass: torque to manufacturer specification (typically 110-120 lb-ft for F-150, verify with your specific U-bolt kit instructions). This gradual tightening ensures even clamping force and proper plate seating.
9. 9

   Verify axle alignment and clearances
   With U-bolts torqued, verify the axle is centered on the leaf spring and properly seated. Check that there is adequate clearance between the U-bolts and brake lines, shock absorbers, and exhaust components. Adjust jack height slightly if needed to verify suspension articulation clearances.
10. 10

    Repeat for opposite side
    If replacing U-bolts on both sides, repeat steps 2 through 9 for the opposite rear leaf spring. Maintain axle support with the floor jack while working on the second side. Always replace U-bolts in pairs (both sides) for balanced clamping force.
11. 11

    Reinstall wheels
    Reinstall the rear wheels, threading lug nuts on by hand initially. Lower the vehicle slowly from the jack stands using the floor jack, keeping jack stands in place until weight is on wheels. Remove jack stands, then lower vehicle completely to the ground.
    Torque spec

    Wheel Lug Nuts169 Nm (125 lb-ft)
12. 12

    Final torque verification
    With vehicle weight on the suspension, perform a final torque check on all U-bolt nuts using the crisscross pattern. This is critical as suspension loading may slightly affect torque values. Verify all nuts meet specification. Torque wheel lug nuts to 125 lb-ft in a star pattern.
    Torque spec

    Wheel Lug Nuts169 Nm (125 lb-ft)

Reassembly

1. After 50-100 miles of driving, re-torque U-bolt nuts to specification as initial settling may occur
2. Check U-bolt torque again after 500 miles to ensure proper retention
3. Always replace U-bolts in pairs (both sides) for consistent clamping force and suspension performance

Verification

• Test drive vehicle at low speed and verify no unusual noises, vibrations, or handling changes
• Visually inspect U-bolt installation to confirm nuts are tight and no gaps exist between backing plate and spring
• Check for adequate clearance between U-bolts and surrounding components during suspension travel
• Verify axle appears centered on leaf springs when viewed from behind vehicle
• Schedule re-torque check after 50-100 miles of normal driving

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