Radius Arm

Removal and replacement of the front radius arm (also called lower control arm or I-beam radius arm) on the twin I-beam front suspension of a 1972 Ford F-100.

Warnings

Tools required

Parts

• Radius arm (lower control arm) × 1 — Use OEM specification or quality aftermarket
• Radius arm bushing kit (front and rear) × 1 — Use OEM specification
• Radius arm to axle bolt × 1 — Use OEM specification
• Radius arm to frame bolt × 1 — Use OEM specification
• Lock washers for radius arm bolts × 2 — Use OEM specification
• Cotter pin (for lower ball joint) × 1 — Use OEM specification

Preparation

1. Park vehicle on level, solid ground and engage parking brake
2. Place wheel chocks behind rear wheels
3. Loosen front wheel lug nuts while vehicle is on ground (do not remove)
4. Apply penetrating oil to radius arm bolts, lower ball joint nut, shock absorber bolts, and spring seat components
5. Raise front of vehicle with floor jack at frame crossmember
6. Support vehicle securely on jack stands placed under frame rails behind front suspension
7. Remove front wheel completely

Procedure

1. 1

   Support the front axle I-beam
   Position floor jack under the front axle I-beam near the radius arm attachment point. Raise jack just enough to contact the axle beam and take slight load off the suspension, but do not lift the vehicle. This supports the weight of the axle and prevents it from dropping when components are disconnected. Verified detail (On the Twin I-Beam suspension the radius arm is not a lower control arm. This label may cause the customer to order the wrong part.): Radius arm (I-beam radius arm / axle-to-frame locating arm)
2. 2

   Compress the coil spring
   Install coil spring compressor through the center of the coil spring following manufacturer instructions. Compress the spring gradually, alternating sides of the compressor tool evenly, until there is approximately 1-2 inches of free play and the spring is no longer under tension against the upper and lower spring seats. Count the number of turns on each side of the compressor to ensure even compression.
3. 3

   Disconnect the shock absorber
   Remove the lower shock absorber mounting bolt and nut from the radius arm bracket. The shock absorber can swing up and out of the way or be removed completely from the upper mount if access is limited. Support the shock to prevent it from hanging on the hydraulic line if equipped.
4. 4

   Disconnect the lower ball joint from spindle
   Remove the cotter pin from the lower ball joint castle nut. Remove the castle nut from the ball joint stud. Use a ball joint separator tool (pickle fork or puller-type) to separate the ball joint stud from the steering knuckle/spindle. Strike the separator tool firmly with a hammer if using pickle fork type. The spindle will remain supported by the upper ball joint.
5. 5

   Remove radius arm to axle bolt
   Locate the through-bolt that connects the front of the radius arm to the front axle I-beam. This is a large diameter bolt that passes horizontally through the axle beam and the front bushing of the radius arm. Remove the nut and lock washer from one end, then drive the bolt out using a drift punch or brass hammer. The bolt may be heavily corroded and require significant force or additional penetrating oil.
6. 6

   Remove radius arm to frame bolt
   Locate the rear mounting bolt where the radius arm attaches to the frame bracket. This bolt passes through the rear bushing of the radius arm and the frame-mounted bracket. Remove the nut and lock washer, then remove the bolt. You may need to pry the radius arm slightly to relieve pressure on the bolt.
7. 7

   Remove the radius arm assembly
   With both mounting bolts removed, lower the floor jack slightly to allow clearance. Maneuver the radius arm down and out from between the axle I-beam and frame bracket. The coil spring will remain in place on its upper and lower seats.
8. 8

   Inspect and prepare new radius arm
   Inspect the new radius arm for correct fitment and proper bushing installation. If bushings are not pre-installed, press in new bushings at front and rear mounting points using appropriate bushing driver or hydraulic press. Ensure bushings are seated flush and oriented correctly. Clean all mounting hardware with wire brush and inspect threads.
9. 9

   Install new radius arm to frame bracket
   Position the new radius arm with the rear mounting eye aligned with the frame bracket. Insert the frame mounting bolt through the bracket and radius arm rear bushing. Install lock washer and nut, but do not fully tighten at this time. Leave fastener snug enough to hold position but with ability to pivot.
10. 10

    Install radius arm to front axle
    Raise the floor jack to position the front axle I-beam at proper height to align with the front bushing of the radius arm. Align the holes in the axle beam with the radius arm front bushing. Insert the through-bolt from the appropriate side and install lock washer and nut on the opposite end. Again, snug but do not fully tighten.
11. 11

    Reconnect lower ball joint to spindle
    Use the floor jack to raise or lower the axle beam as needed to align the lower ball joint stud with the hole in the steering knuckle/spindle. Insert the ball joint stud into the spindle and install the castle nut. Tighten the castle nut to specification and install a new cotter pin through the castle nut slots and ball joint stud. Bend cotter pin ends to secure.
12. 12

    Release spring compressor
    If the coil spring was left compressed in place, gradually release tension on the spring compressor tool, alternating sides evenly. Ensure the spring seats properly in both upper and lower spring seat pockets as tension is released. Remove the spring compressor tool once spring is fully seated and under normal load.
13. 13

    Reconnect shock absorber
    Position the lower end of the shock absorber to the mounting bracket on the radius arm. Insert the lower shock mounting bolt and install the nut. Tighten the shock absorber mounting bolt to 52.0 lb-ft (70.0 Nm) the shock in place.
14. 14

    Final tightening of radius arm bolts
    With the vehicle weight now on the suspension (supported by jack under axle), torque the radius arm mounting bolts to final specification. Both the front axle bolt and rear frame bolt should be torqued with the suspension at normal ride height to prevent bushing bind. Lower the floor jack slightly if needed to achieve normal suspension position before final torque.
15. 15

    Reinstall wheel and lower vehicle
    Reinstall the front wheel and thread lug nuts by hand. Lower the vehicle until the tire just contacts the ground. Torque lug nuts to specification in a star pattern. Fully lower vehicle and remove jack stands. Torque lug nuts again in star pattern with vehicle on ground.

Reassembly

1. All suspension fasteners must be torqued to specification with vehicle at normal ride height to prevent premature bushing failure
2. Always replace cotter pins with new pins - never reuse old cotter pins on suspension components
3. Verify coil spring is properly seated in upper and lower spring pockets after reassembly
4. Check that shock absorber is securely mounted and not binding through full suspension travel

Verification

• Test drive vehicle at low speed in safe area and listen for any unusual noises from front suspension
• Perform visual inspection underneath vehicle for any loose fasteners or components
• Check wheel alignment - radius arm replacement will affect camber and caster settings, professional alignment is recommended
• Verify steering returns to center properly and there is no pulling to either side
• Inspect all fasteners after 50-100 miles of driving and re-torque if necessary

More procedures for this vehicle