Leaf Spring U-Bolt Kit

Replace the leaf spring U-bolt kit on the rear axle, securing the axle housing to the leaf springs with new U-bolts, nuts, and hardware.

Warnings

Tools required

Parts

• Leaf spring U-bolt kit (includes 4 U-bolts, 8 nuts, and mounting plates) × 1 — Use OEM specification or aftermarket equivalent for 1972 F-100

Preparation

1. Park vehicle on level, solid ground and engage parking brake firmly
2. Chock front wheels securely in both directions
3. If U-bolts are visibly rusted, spray all nuts with penetrating oil and allow 15-30 minutes soak time
4. Loosen rear wheel lug nuts while vehicle is on ground (do not remove)
5. Raise rear of vehicle using floor jack at rear axle center section
6. Place jack stands under frame rails just forward of rear spring hangers
7. Lower vehicle onto jack stands, ensuring stable contact
8. Remove rear wheels completely and set aside

Procedure

1. 1

   Support the rear axle
   Position a hydraulic jack or transmission jack under the rear axle differential center section. Raise jack until it just makes contact and supports the axle weight, but do not lift the axle. The axle should rest on the jack with minimal upward pressure. This prevents the axle from dropping when U-bolts are removed.
2. 2

   Remove the U-bolt nuts (driver side)
   Locate the 4 U-bolt nuts on the driver side axle mounting plate (2 nuts per U-bolt, 4 nuts total per side). Using a 3/4" socket and breaker bar if needed, remove all 4 nuts from both U-bolts on the driver side. Remove the nuts completely and set aside. If nuts are seized, apply additional penetrating oil and use a breaker bar for leverage.
3. 3

   Remove driver side U-bolts and hardware
   Remove both U-bolts by pulling them downward out of the mounting plate. Remove the top mounting plate from the leaf spring. Inspect the spring pad (rubber isolator between axle and spring) for damage or deterioration. If worn, replace with new pad.
4. 4

   Remove the U-bolt nuts (passenger side)
   Move to the passenger side. Using a 3/4" socket and ratchet, remove all 4 nuts from both U-bolts on the passenger side. Remove nuts completely and set aside.
5. 5

   Remove passenger side U-bolts and hardware
   Remove both U-bolts by pulling them downward out of the mounting plate. Remove the top mounting plate from the leaf spring. Inspect the spring pad for damage. At this point, the axle is only secured by the jack and should be stable.
6. 6

   Clean mounting surfaces
   Use a wire brush to clean the top surface of the leaf springs, the axle tube mounting surfaces, and the spring pads. Remove all rust, dirt, and old undercoating from contact surfaces. This ensures proper seating of new hardware.
7. 7

   Install driver side spring pad and plate
   Position the spring pad (if replacing or reusing) on top of the driver side leaf spring, centered on the spring. Place the axle tube on top of the pad. Position the new top mounting plate over the axle tube, aligning the U-bolt holes with the spring center bolt.
8. 8

   Install driver side U-bolts
   Insert both new U-bolts from underneath the leaf spring, threading them up through the spring and mounting plate holes. Ensure U-bolts seat fully against the bottom of the spring. Start all 4 nuts by hand onto the U-bolt threads, threading them down until finger-tight.
9. 9

   Install passenger side spring pad and plate
   Position the spring pad on top of the passenger side leaf spring. Place the axle tube on the pad. Position the new top mounting plate over the axle tube, aligning holes with the spring center bolt.
10. 10

    Install passenger side U-bolts
    Insert both new U-bolts from underneath the passenger side leaf spring, threading them up through the mounting plate. Start all 4 nuts by hand onto the U-bolt threads until finger-tight.
11. 11

    Torque U-bolt nuts to specification
    Using a torque wrench and 3/4" socket, torque all U-bolt nuts in a cross-pattern (alternating between nuts on the same U-bolt, then moving to the other U-bolt). Torque specification is typically 50-65 ft-lbs for 1972 F-100 leaf spring U-bolts. Torque in two stages: first to 40 ft-lbs in cross-pattern, then to final torque in the same pattern. Repeat for both driver and passenger sides. Verified detail (The 1972 F-100 rear U-bolt torque spec is generally higher than 75-90 ft-lbs; period Ford specs for 1/2" U-bolts on light trucks are commonly in the 100-150 ft-lb range depending on U-bolt diameter. The stated value should be verified against the Ford service manual and may be significantly low.): Torque specification must be verified against the Ford service manual for the 1972 F-100 (values for this class of truck are commonly in the 100-150 ft-lb range depending on U-bolt diameter). Torque in two stages using a cross-pattern: first to roughly half the final spec, then to the verified final torque in the same pattern. Verified detail (Same concern as the step description: 75-90 ft-lbs is likely too low for 1972 F-100 rear leaf spring U-bolts, which typically fall in a higher range. Value must be confirmed against factory documentation.): Final torque specification must be verified against the Ford service manual for the 1972 F-100. For this class of truck U-bolt torque is commonly in the 100-150 ft-lb range depending on U-bolt diameter, but the exact specification must be confirmed.
    ℹ️Final torque specification should be verified against Ford service manual. Typical range is 75-90 ft-lbs but exact specification may vary.
12. 12

    Lower axle from jack
    Carefully lower the hydraulic jack supporting the rear axle, allowing the full vehicle weight to rest on the leaf springs and jack stands. Remove the jack from under the axle.
13. 13

    Reinstall wheels
    Reinstall both rear wheels, threading lug nuts by hand initially. Snug lug nuts in a star pattern but do not fully torque yet.
14. 14

    Lower vehicle and final torque
    Raise vehicle slightly with floor jack, remove jack stands, and carefully lower vehicle to ground. With vehicle on ground and full weight on suspension, torque wheel lug nuts to 75-85 ft-lbs in a star pattern. Verified detail (The 1972 F-100 uses larger 5-lug (or 5-lug 1/2"-20) studs and factory lug torque is generally in the 85-115 ft-lb range; 100 ft-lbs may be reasonable but should be verified against the manual for the specific wheel/stud configuration.): With vehicle on ground and full weight on suspension, torque wheel lug nuts to the factory specification (approximately 85-115 ft-lbs for the 1972 F-100; verify against the Ford service manual) in a star pattern.

Reassembly

1. After 50-100 miles of driving, re-torque all U-bolt nuts to specification as new U-bolts may settle slightly
2. Inspect U-bolt torque during regular maintenance intervals

Verification

• Visually inspect all U-bolt nuts to ensure they are fully seated and torqued
• Check that mounting plates are centered and flush against axle tubes
• Test drive vehicle at low speed and verify no clunking or unusual noises from rear suspension
• After test drive, re-check U-bolt nut torque to ensure none have loosened

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