Subframe

Remove and replace the front subframe assembly on a 2007-2013 Mercedes-Benz S65 AMG, including disconnection of all control arms, steering components, and mounting hardware.

Warnings

Tools required

Parts

• Front subframe assembly × 1 — Use OEM specification
• Subframe mounting bolts × 6 — Use OEM specification
• Self-locking nuts for control arms × 4 — Use OEM specification
• Ball joint boots (if damaged) × 2 — Use OEM specification
• Subframe bushings × 6 — Use OEM specification

Fluids

• Pentosin CHF 11S — 1 qt

Preparation

1. Park vehicle on level surface and engage parking brake
2. Disconnect negative battery terminal and wait 10 minutes for airbag system to discharge
3. Raise vehicle and support on jack stands at manufacturer-specified lift points
4. Remove both front wheels
5. Spray all subframe bolts, control arm bolts, and ball joint nuts with penetrating oil and allow to soak for 15 minutes
6. Mark steering wheel center position with tape
7. Take reference measurements from subframe mounting points to body for reinstallation alignment
8. Place transmission jack or subframe support fixture under center of subframe but do not lift

Procedure

1. 1

   Disconnect sway bar links
   Locate the sway bar end links connecting the sway bar to the lower control arms on both sides. Use an Allen key to hold the ball stud shaft while loosening the upper nut with a wrench. Remove both sway bar links completely and set aside for reuse.
   Torque spec

   Sway Bar Link Nuts55 Nm (41 lb-ft)
2. 2

   Separate ball joints from knuckles
   Remove the ball joint castle nuts from both front lower control arms where they connect to the steering knuckles. Use a ball joint separator tool to press the ball joint taper out of the knuckle. Do not use excessive force with a hammer as this can damage the ball joint threads or knuckle.
   ⚠Ball joint separator creates significant force. Ensure tool is properly seated before applying pressure.
   Torque spec

   Ball Joint Nut119 Nm (88 lb-ft)
3. 3

   Disconnect steering rack from subframe
   Locate the steering rack mounting bolts that secure the rack to the subframe. Remove these bolts and carefully support the steering rack with wire or a bungee cord, securing it to the body to prevent strain on the steering column intermediate shaft. Do not disconnect the intermediate shaft unless replacing the rack.
   ⚠Do not allow steering rack to hang by power steering lines or intermediate shaft.
4. 4

   Disconnect power steering lines
   Place a drain pan under the power steering rack. Disconnect the pressure and return lines from the steering rack using a flare nut wrench to prevent rounding. Cap or plug all openings immediately to prevent contamination. Allow fluid to drain completely.
   ⚠Power steering fluid will drain when lines are disconnected. Collect fluid properly and dispose according to local regulations.
5. 5

   Remove strut lower mounting bolts
   Locate the strut-to-knuckle pinch bolts on both sides. These are large bolts that pass through the strut and steering knuckle. Remove these bolts completely. The knuckle will now be free to swing but should remain connected to the upper control arm.
   ⚠Support the knuckle assembly to prevent sudden movement when strut bolt is removed.
   Torque spec

   Strut Bolts156 Nm (115 lb-ft)
6. 6

   Disconnect control arms from subframe
   Locate all control arm mounting points to the subframe - both lower control arms will have front and rear mounting points. Remove the bolts securing the control arms to the subframe only, leaving the control arms attached to the knuckles. Note the orientation and position of any eccentric bolts or washers used for alignment adjustment.
   ℹ️Mark eccentric bolt positions with paint or take photographs before removal to preserve alignment settings.
   Torque spec

   Control Arm Bolts165 Nm (122 lb-ft)
7. 7

   Disconnect additional subframe-mounted components
   Identify and disconnect any additional components mounted to the subframe including engine mount brackets, transmission mount connections, ABS sensor wiring clips, brake line brackets, and auxiliary cooler lines if equipped. Label all electrical connectors and note routing for reassembly.
   ℹ️Take photographs of all component locations and wire routing before disconnection.
8. 8

   Support and lower subframe
   Ensure the transmission jack or subframe support fixture is properly positioned under the center of the subframe with adequate surface contact. Raise the support slightly to take the weight off the mounting bolts. Remove all subframe mounting bolts - typically 6 total mounting points (2 front, 2 middle, 2 rear). Slowly and carefully lower the subframe, maintaining level orientation. Guide it clear of all components and lines.
   ⚠️Subframe must be lowered slowly and evenly. Have an assistant guide the subframe and watch for any snagged components, wires, or lines.
   ⚠Verify all components are disconnected before lowering. Forced lowering can damage brake lines, wiring, or other components.
   Torque spec

   Mounting Bolts37 Nm (27 lb-ft)
9. 9

   Inspect and prepare new subframe
   With the old subframe removed, inspect all mounting points on the vehicle body for damage, corrosion, or elongated bolt holes. Clean all mounting surfaces with a wire brush. If installing a new subframe, transfer any reusable components such as brackets, heat shields, or mounting hardware. Install new subframe bushings if included with the replacement subframe. Clean all bolt threads and apply anti-seize to non-critical fasteners.
   ℹ️Do not apply thread locker or anti-seize to bolts requiring torque-to-yield or specified torque values unless explicitly called for by manufacturer.
10. 10

    Install subframe assembly
    Position the new or serviced subframe on the support fixture and carefully raise it into position under the vehicle. Align all mounting points with body mounting locations using reference marks made during removal. Install all 6 mounting bolts finger-tight initially. Use alignment pins or measuring tools to ensure subframe is centered and square to the body before tightening. Torque all mounting bolts to specification in a cross-pattern sequence starting from the center and working outward.
    ⚠Subframe alignment is critical for proper suspension geometry and handling. Verify measurements match specifications before final tightening.
    Torque spec

    Mounting Bolts37 Nm (27 lb-ft)
11. 11

    Reconnect control arms and suspension components
    Reconnect all control arms to their subframe mounting points. Install new self-locking nuts where applicable. Align any eccentric bolts to their marked positions. Do NOT torque these bolts yet - they must be torqued with vehicle weight on the wheels. Reconnect the strut lower mounting bolts on both sides and torque to specification. Reconnect ball joints to steering knuckles and torque castle nuts to specification, installing new cotter pins.
    Torque spec

    Strut Bolts156 Nm (115 lb-ft)

    Ball Joint Nut119 Nm (88 lb-ft)
12. 12

    Reinstall steering rack and components
    Position the steering rack back onto the subframe mounting points and install mounting bolts. Reconnect power steering pressure and return lines using new O-rings or sealing washers. Torque all steering rack mounting hardware to specification. Reattach all brackets, wiring clips, and ABS sensor wiring to the subframe.
    ℹ️Ensure power steering lines are not kinked or twisted during installation.
13. 13

    Reconnect sway bar links
    Install both sway bar end links connecting the sway bar to the lower control arms. Hold the ball stud with an Allen key and torque the nuts to specification. Verify the sway bar moves freely and is not binding.
    Torque spec

    Sway Bar Link Nuts55 Nm (41 lb-ft)
14. 14

    Install wheels and perform initial torque
    Install both front wheels and torque lug nuts to specification in a star pattern. Lower the vehicle until the suspension is at normal ride height but keep jack stands in place as a safety backup. With vehicle weight on the wheels, torque all control arm mounting bolts to specification. This is critical as these bolts must be torqued under load to prevent bushing bind.
    ⚠Control arm bolts MUST be torqued with vehicle weight on suspension. Torquing while suspended will cause premature bushing failure.
    Torque spec

    Wheel Lug Nuts183 Nm (135 lb-ft)

    Control Arm Bolts165 Nm (122 lb-ft)
15. 15

    Complete final assembly and fluid service
    Raise vehicle and remove jack stands, then lower completely to ground. Reconnect negative battery terminal. Fill power steering reservoir with Pentosin CHF 11S to proper level. Start engine and turn steering wheel lock-to-lock several times slowly to bleed air from power steering system. Check for leaks at all power steering connections. Top off power steering fluid as needed. Verify all components are properly secured.
    ⚠Do not turn steering wheel rapidly during bleeding process as this can aerate fluid and damage pump.

Reassembly

1. Verify all fasteners are torqued to specification, particularly control arm bolts which must be torqued with vehicle weight on wheels
2. Reconnect battery and clear any fault codes related to the repair using a Mercedes-Benz compatible scan tool
3. Test power steering operation at idle and verify no leaks are present
4. Road test at low speeds in a safe area to verify no abnormal noises or handling issues before proceeding to alignment

Verification

• Schedule and complete a four-wheel alignment immediately - vehicle is not safe for normal driving without proper alignment
• Verify steering wheel is centered when driving straight and steering returns to center properly
• Check for any unusual noises from suspension during low-speed driving over bumps
• Re-check all mounting bolt torques after 50-100 miles of driving
• Inspect all power steering connections for leaks after driving and verify fluid level is correct
• Verify no warning lights are present on instrument cluster related to suspension or steering systems

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