Radius Arm

This procedure covers removal and replacement of the front radius arm (also called upper control arm) on a 4WD Dodge Ram 2500 with the 5.9L Cummins diesel engine.

Warnings

Tools required

Parts

• Radius arm (upper control arm) × 1 — Use OEM specification or quality aftermarket
• Cotter pin (ball joint) × 1 — Standard 1/8 inch
• Anti-seize compound × 1 — Use OEM specification

Preparation

1. Park vehicle on level surface and engage parking brake
2. Place wheel chocks behind rear wheels
3. Spray all radius arm bolts, ball joint nut, and mounting hardware with penetrating oil and allow to soak for 15-20 minutes
4. Loosen front wheel lug nuts while vehicle is on ground (do not remove)
5. Raise front of vehicle with floor jack at frame rail
6. Support vehicle securely on jack stands placed under frame rails behind front suspension
7. Remove wheel and tire assembly completely

Procedure

1. 1

   Remove ball joint cotter pin
   Locate the radius arm connection point at the axle housing. The radius arm bolts to a bracket on the front axle and to the frame; it does not attach to the steering knuckle. No ball joint or cotter pin is involved at the radius arm connection. If the cotter pin is corroded, use a punch and hammer to drive it through.
2. 2

   Loosen ball joint nut
   There is no ball joint castle nut on the radius arm connection; this step does not apply to radius arm replacement on a solid-axle Ram 2500. Leave the nut threaded on approximately 2-3 turns to protect the ball joint stud threads during separation.
3. 3

   Separate ball joint from knuckle
   Insert a ball joint separator or pickle fork between the steering knuckle and the radius arm ball joint. Strike the separator with a hammer to break the taper fit. Once the joint is loose, remove the castle nut completely. Support the radius arm with your hand or a jack as you remove the nut to prevent it from falling.
   ⚠Using a pickle fork will damage the ball joint boot. Only use if replacing the radius arm or ball joint.
4. 4

   Remove front radius arm mounting bolt
   Locate the front mounting point where the radius arm attaches to the frame rail. The bolt passes horizontally through the frame bracket. Using the correct socket and wrench sizes as specified in the factory service manual (verify fastener size before starting; radius arm bolts on this platform are large-diameter), remove the front mounting bolt completely. Note the orientation of any washers or bushings. Note the orientation of any washers or bushings.
5. 5

   Remove rear radius arm mounting bolts
   The rear of the radius arm is secured to the frame-mounted bracket. Verify the number and size of fasteners against the factory service manual before removal, then remove the rear mounting hardware. Support the radius arm as you remove the final bolt to prevent it from falling. Support the radius arm as you remove the final bolt to prevent it from falling.
6. 6

   Remove radius arm from vehicle
   Carefully lower and remove the radius arm assembly from the vehicle. Inspect the ball joint taper seat in the knuckle for damage or corrosion. Clean the ball joint mounting area on the knuckle with a wire brush.
7. 7

   Prepare new radius arm
   Compare the new radius arm to the old unit to verify correct replacement part. Inspect all bushings and ball joint for proper installation and condition. Apply a thin coat of anti-seize to the ball joint stud threads and the mounting bolt threads.
8. 8

   Install radius arm to frame
   Position the new radius arm into the frame mounting brackets. Install the rear mounting bolts finger-tight first to hold the arm in position, then install the front mounting bolt finger-tight. Do not fully torque these bolts yet.
9. 9

   Connect ball joint to knuckle
   Reconnect the radius arm to the axle bracket, aligning the mounting holes (a pry bar may help align them). Install the mounting hardware and tighten per factory specification. There is no ball joint or castle nut at the radius arm connection.
   Torque spec

   Ball Joint Nut88 Nm (65 lb-ft)
10. 10

    Install new cotter pin
    Align the castle nut slots with the hole in the ball joint stud. If necessary, tighten the nut slightly (never loosen) to align the slots. This step does not apply; the radius arm connection uses bolted fasteners, not a cotter-pinned ball joint stud.
11. 11

    Preliminary tighten mounting bolts
    Snug all radius arm mounting bolts (front and rear) but do not torque to final specification yet. The control arm bolts must be torqued with the vehicle weight on the suspension to prevent bushing bind.
12. 12

    Reinstall wheel and lower vehicle
    Install the wheel and tire assembly. Thread lug nuts by hand to prevent cross-threading, then snug them in a star pattern with a socket. Lower the vehicle until the suspension is at normal ride height but the jack is still supporting some weight.
13. 13

    Torque control arm mounting bolts
    With the vehicle weight on the suspension (still supported by jack but tires touching ground), torque the front and both rear radius arm mounting bolts to specification. This ensures the bushings are not pre-loaded in a twisted position. Schedule a front end alignment within 50 miles of completing this repair, as radius arm replacement affects caster (and pinion angle) on this solid-axle truck; camber is fixed by the axle.
    Torque spec

    Control Arm Bolts165 Nm (122 lb-ft)
14. 14

    Final wheel installation
    Fully lower the vehicle to the ground and remove the jack. Torque the wheel lug nuts to specification in a star pattern using a torque wrench.
    Torque spec

    Wheel Lug Nuts183 Nm (135 lb-ft)

Reassembly

1. Ensure all fasteners are torqued to specification
2. Verify cotter pin is properly installed and bent to prevent backing out
3. Check that no tools or parts were left in the wheel well
4. Repeat procedure for opposite side if replacing both radius arms

Verification

• Test drive vehicle at low speed in a safe area and verify no unusual noises from front suspension
• Check for proper steering response and no pulling to one side
• Verify no clunking or looseness when driving over bumps
• Schedule a front end alignment within 50 miles of completing this repair, as radius arm replacement affects camber and caster settings
• Re-torque all fasteners after 100 miles of driving

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