Upper Control Arm - Front

This procedure removes and replaces the front upper control arm on a 2019 Mercedes-Benz G-Class with 4.0L Turbo V8 engine, requiring disconnection of the ball joint and control arm mounting bolts.

Warnings

Tools required

Parts

• Front upper control arm × 1 — Use OEM specification
• Control arm mounting bolts (if damaged) × 2 — Use OEM specification
• Ball joint castle nut (if damaged) × 1 — Use OEM specification

Preparation

1. Park vehicle on level ground and engage parking brake
2. Place wheel chocks behind rear wheels
3. Loosen front wheel lug nuts while vehicle is on the ground (do not remove)
4. Raise front of vehicle with floor jack at designated jacking points
5. Secure vehicle on jack stands rated for vehicle weight
6. Remove front wheel completely
7. Spray penetrating oil on control arm bolts and ball joint nut; allow to soak for 10-15 minutes

Procedure

1. 1

   Support the knuckle assembly
   Position a floor jack under the lower control arm or knuckle assembly with a block of wood to distribute load. Raise jack until it just contacts and slightly supports the assembly. This prevents the suspension from dropping when the upper control arm is disconnected.
2. 2

   Remove ball joint castle nut
   Locate the upper ball joint stud where it connects to the steering knuckle. There is no cotter pin on this design. Using the appropriate socket, remove the self-locking ball joint nut securing the upper ball joint to the knuckle. Discard the nut; the ball joint self-locking nut is a single-use fastener and must be replaced with a new one. Note: Ball joint self-locking nut (replace)
3. 3

   Separate the ball joint from knuckle
   Insert a ball joint separator or pickle fork between the upper control arm ball joint and the steering knuckle. Strike the tool with a hammer or use a press-type separator to break the taper connection. The ball joint stud will pop free from the knuckle. If using a pickle fork, note that this may damage the ball joint boot if reusing the control arm.
   ⚠Ball joint may separate suddenly. Ensure the knuckle is supported by the floor jack to prevent dropping.
4. 4

   Remove front control arm mounting bolt
   Locate the front mounting bolt that secures the upper control arm to the chassis or subframe. This bolt typically passes through a bushing at the front of the control arm. Using the appropriate socket (verify head type — typically an external hex head bolt on this chassis), remove the front mounting bolt completely and set aside. Note the orientation and any washers or spacers.
5. 5

   Remove rear control arm mounting bolt
   Locate the rear mounting bolt that secures the upper control arm to the chassis or subframe. Using the appropriate socket (verify head type — typically an external hex head bolt on this chassis), remove the rear mounting bolt completely. Note the orientation and any washers or spacers.
6. 6

   Remove upper control arm
   With both mounting bolts removed and the ball joint separated, carefully maneuver the upper control arm out of the mounting position. You may need to rotate or angle the arm to clear the knuckle and chassis. Inspect the removed arm for wear, damage, or torn bushings to confirm replacement is necessary.
7. 7

   Clean mounting surfaces
   Use a wire brush to clean the mounting bolt holes in the chassis and subframe. Remove any rust, dirt, or debris from the ball joint taper seat in the steering knuckle. Inspect the knuckle taper for damage or excessive wear. Clean threads on mounting bolts if reusing.
8. 8

   Install new upper control arm
   Position the new upper control arm into the mounting location. Align the control arm bushings with the chassis mounting points. Insert the ball joint stud into the steering knuckle taper seat. You may need to use the floor jack to raise or lower the knuckle slightly to align the ball joint stud properly.
9. 9

   Install mounting bolts finger-tight
   Insert the front and rear control arm mounting bolts through the bushings and into the chassis. Thread both bolts in by hand until finger-tight. Do not fully torque at this stage. Ensure any washers or spacers are in their original positions.
10. 10

    Install and torque ball joint nut
    Thread a NEW self-locking nut onto the ball joint stud by hand, ensuring it threads smoothly. Using a torque wrench and appropriate socket, torque the ball joint nut to specification. Hold the ball joint stud with a hex key or Torx bit if it spins during tightening.
    Torque spec

    Upper Ball Joint Nut101 Nm (75 lb-ft)
11. 11

    Torque control arm mounting bolts
    With the suspension at approximately ride height (floor jack supporting knuckle), torque the front and rear control arm mounting bolts to specification. These bolts must be torqued with the suspension loaded to prevent bushing bind. Verify the factory-specified tightening sequence.
    Torque spec

    Control Arm Bolts148 Nm (109 lb-ft)
12. 12

    Remove support jack and reinstall wheel
    Carefully lower and remove the floor jack from under the knuckle assembly. Position the wheel onto the hub and thread all lug nuts by hand. Using the appropriate socket (typically 17mm on this vehicle), thread the wheel bolts in a star pattern until snug but do not fully torque yet.
13. 13

    Lower vehicle and torque lug nuts
    Raise vehicle slightly to remove jack stands, then carefully lower vehicle to the ground. With full vehicle weight on the wheels, torque all lug nuts in a star pattern to specification using a torque wrench.
    Torque spec

    Wheel Lug Nuts142.4 Nm (105 lb-ft)

Reassembly

1. Ensure all fasteners are torqued to specification with suspension at ride height
2. Verify ball joint castle nut cotter pin is properly installed if equipped
3. Check that no tools or parts were left in the wheel well
4. If both sides were replaced, verify all fasteners on both sides are properly torqued

Verification

• Test drive vehicle at low speed in a safe area and listen for any unusual noises from the front suspension
• Check for proper steering response and ensure no pulling to either side
• Perform a visual inspection of the control arm installation to confirm no interference or contact with other components
• Schedule a professional wheel alignment — replacing upper control arms will alter camber and caster settings
• After 50-100 miles of driving, re-check torque on all fasteners to ensure nothing has loosened

Related trouble codes on this vehicle

Codes that commonly send this job to the bay — tap one for symptoms, causes, and diagnostic steps.

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