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Clunk Noise from Front of Vehicle (Replace Left Front Mount Bracket)

Subject:Clunk Noise From Front of Vehicle (Replace Left Front Mount Bracket, Add Reinforcements to Frame and Bracket)

Models:1999 Chevrolet and GMC K1500 Series Pickup Models (Silverado and Sierra)


Condition

Some customers may comment on a clunk noise coming from the front of the vehicle. Vehicles exposed to extreme off-road conditions or snow plowing are more prone to develop this condition.

Cause

The condition may be caused by a left front axle mount bracket crack at the frame due to an area of high stress.

Correction

A differential carrier support kit has been developed to distribute the load of the axle away from the area of high stress where crack initiation may occur. Replace the left front axle mount bracket. Add reinforcements to the frame and bracket. Use the following service procedure.

  1. Disconnect the negative terminal from the battery.
  2. Raise the vehicle. Place a jack or utility stands at the rear of the vehicle.
  3. Remove both of the front tire and wheel assemblies.
  4. Remove the differential carrier shield.
  5. Reference mark the relationship of the propeller shaft to the front drive axle pinion yoke.
  6. Remove the yoke retainer bolts and the yoke retainers from the front axle pinion yoke.

    7. Notice: When removing the propeller shaft, do not attempt to remove the shaft by pounding on the yoke ears or using a tool between the yoke and the universal joint. If the propeller shaft is removed by using such means, the injection joints may fracture and lead to premature failure of the joint.

  7. Disconnect the propeller shaft from the front axle pinion yoke. Wrap the bearing caps with tape in order to prevent the loss of bearing rollers.
  8. Support the propeller shaft and move out of the way as necessary.
  9. Remove the bolts securing both wheel drive shaft inboard flanges to the output shaft flanges.

    10. Object Number: 339503 Size: SH
  10. Remove the inner axle housing nuts (2) from the bracket (1).
  11. Disconnect the electrical connections and the wiring harness retainers from the front differential carrier.
  12. Disconnect the vent hose.

    13. Object Number: 345350 Size: SH
  13. Remove the differential carrier assembly lower mounting bolt (3) and nut (4).

    14. Object Number: 340481 Size: SH

    Important: Do not reuse the idler arm and pitman arm ball stud nuts.

  14. Remove the idler arm ball stud nut (10) and disconnect the idler arm (1) from the relay rod (9) using the J 24319-B.

    15. Notice: Do not hammer on the pitman arm, pitman arm shaft or puller. Damage to the pitman arm or steering gear may result.

  15. Remove the pitman arm ball stud nut (8) and disconnect the pitman arm (2) from the relay rod (9) using the J 24319-B.
  16. Attach a transmission jack to the carrier assembly.
  17. Remove the differential carrier assembly upper mounting bolt (1) and nut (2).
  18. Remove the differential carrier assembly from the vehicle.

    19. Object Number: 340417 Size: SH
  19. Remove the steering gear frame bolts and reposition the steering gear.
  20. Remove the stands and lower the vehicle.

    21. Object Number: 307275 Size: SH
  21. Remove the bolts retaining the RH and LH upper engine mount to the lower engine mount.
  22. Raise the vehicle. Place a jack or utility stands at the rear of the vehicle.
  23. Raise and support the engine with a suitable jack.
  24. Remove the LH lower engine mount bracket through bolts and bracket.
  25. Block the engine in the raised position using a piece of wood between the oil pan and crossmember.
  26. Remove the support from the engine.
  27. Clean the axle mounting bracket area with a wire brush in order to determine the full extent of the cracks.
  28. Remove the existing differential carrier bracket from the sidemember using a reciprocating saw and cut-off wheel.
  29. Grind off any remaining metal and welds from the sidemember.
  30. Clean off the area using an air gun.

    31. Caution: The underbody coating on the frame will burn if exposed to the extreme of welding. The coating may ignite and/or flash suddenly. Avoid direct contact of the torch to the underbody coating. Always remove the coating so that sufficient area is free of coating for the welding operation to be performed without risk of igniting the coating. Avoid inhalation of fumes from any over-heated or burning underbody coating.

  31. Remove all the underbody coating from the sidemember around the repair area using a solvent. In addition, remove the underbody coating from the top of the sidemember in order to prevent run down and weld contamination.
  32. Repair the cracks in the sidemember.
    33. • Drill a 5 mm (3/16 in) stop hole at the end of all existing cracks.
    • Clean and "V" grind all crack edges.
    • Fill all cracks with weld and grind smooth, making sure all surfaces are level.

    Object Number: 758248 Size: MF
    (a)155 mm (6.10 in)
    (b)35 mm (1.38 in)
    (c)30 mm (1.18 in)
    (d)40 mm (1.57 in)
    (e)141 mm (5.55 in)
    (f)28 mm (1.10 in)
  33. Measure and mark the locations of the reinforcement plates (2). Use the engine lower mount bracket (1) as your reference point.

    34. Object Number: 758249 Size: MF

    Important: Cover the rubber half shaft boot in order to protect the boot from weld spatter.

  34. Weld the reinforcement plates into position. Mig weld the entire edges.
  35. Install the differential carrier assembly into the vehicle. Secure at the following mounting points:
    36. • Inner axle housing nuts to the bracket
    • Lower mounting bolt and nut
  36. Install the new front differential bracket using the bolt and nut. Locate the bracket position to sidemember and tack weld in place.
  37. Remove the differential carrier assembly from the vehicle.

    38. Object Number: 758250 Size: MF
  38. Weld the bracket to the reinforcement plates. Mig weld the entire inner edge of the rear leg and the entire outer edge of the front leg.

    39. Object Number: 758251 Size: MF
  39. Install the brace centered on the bottom of the bracket and butted-up to the sidemember. Mig weld the entire edge.
  40. Install the LH lower engine mount bracket and the through bolts.

    41. Tighten
    Tighten the bolts to 92 N·m (68 lb ft).

  41. Support the engine with a suitable jack and raise to remove the block.
  42. Lower the engine and remove the support.
  43. Remove the stands and lower the vehicle.
  44. Install the bolts retaining the RH and LH upper engine mount to the lower engine mount.

    45. Tighten
    Tighten the bolts to 50 N·m (37 lb ft).


    Object Number: 758252 Size: MF
  45. From under the hood, mig weld the entire inner side edges of the bracket to the bottom brace.
  46. Apply a spray-on black, rubberized undercoating to the repaired area. Overlap the original coating in order to provide an effective corrosion protection.
  47. Raise the vehicle. Place jack or utility stands at the rear of the vehicle.
  48. Apply a spray-on black, rubberized undercoating to the repaired area. Overlap the original coating in order to provide an effective corrosion protection.
  49. Install the steering gear and the gear to frame bolts.

    50. Tighten
    Tighten the bolts to 150 N·m (110 lb ft).

  50. Install the differential carrier assembly to the vehicle.
  51. Install the differential carrier assembly upper mounting bolt and nut.

    52. Tighten
    Tighten the bolt to 100 N·m (75 lb ft).

  52. Install the differential carrier assembly lower mounting bolt and nut.

    53. Tighten
    Tighten the bolt to 100 N·m (75 lb ft).

  53. Install the inner axle housing nuts to the bracket.

    54. Tighten
    Tighten the nuts to 95 N·m (70 lb ft).

  54. Connect the vent hose.
  55. Connect the electrical connections and the wiring harness retainers to the carrier.
  56. Install the bolts that secure both wheel drive shaft inboard flanges to the output shaft flanges.

    57. Tighten
    Tighten the bolts to 78 N·m (58 lb ft).

  57. Install the propeller shaft to the pinion yoke. Align the reference marks made during removal.
  58. Install the yoke retainers and the retainer bolts to the pinion yoke.

    59. Tighten
    Tighten the yoke retainer bolts to 25 N·m (19 lb ft).

  59. Connect the relay rod to the pitman arm ball stud and install the new nut.

    60. Tighten
    Tighten the nut to 62 N·m (46 lb ft).

  60. Connect the relay rod to the idler arm ball stud and install the new nut.

    61. Tighten
    Tighten the nut to 62 N·m (46 lb ft).

  61. Install the differential carrier shield.
  62. Install both of the front tire and wheel assemblies.
  63. Remove the supports and lower the vehicle.
  64. Connect the negative terminal to the battery.

Parts Information

Part Number

Description

Qty

15056098

Support Kit - Diff. Carrier

1

11516074

Nut

2

Parts are currently available from GMSPO.

Warranty Information

For vehicles repaired under warranty, use:

Labor Operation

Description

Labor Time

F2122

Carrier Assy., Front Differential - R&R

Use published labor operation time

Add

To Replace Left Front Axle Mount Bracket and Add Reinforcements

2.4 hrs

Add

To Repair Frame Cracks

0.6 hr