GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2005 🢒 TopKick C-Series (Crew) C4/C5 🢒 General Information 🢒 Vibration Diagnosis and Correction 🢒 Vibration Analysis - Engine/Accessory Isolation

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. A loose, damaged, misaligned, or defective powertrain insulator and/or bracket may create a transfer path into the passenger compartment.

    2.

  2. A loose, damaged, misaligned, or defective exhaust system insulator and/or bracket may create a transfer path into the passenger compartment.

    3.

  3. Incorrectly seated and/or aligned powertrain components and/or exhaust system components may create a transfer path into the passenger compartment.

    When loosening powertrain mounts in order to re-bed the powertrain observe the following:

    Do not loosen the mount bracket-to-engine bolts/nuts, do not loosen the mount bracket-to-vehicle frame bolts/nuts if mount brackets are used.

    Loosen the mount-to-mount bracket bolts/nuts if mount brackets are used, or loosen the mount-to-slotted holes in vehicle frame bolts/nuts if a direct-mount design is used.

    4.

  4. Non-rotating engine driven accessory components can no longer produce a unique disturbance. If a disturbance is still present, but the characteristics have been altered, it is possible that these component systems are acting as a transfer path for engine firing frequency or a first order engine disturbance.

    If a disturbance is still present, but the characteristics have NOT been altered, it is NOT likely that these component systems are acting as a transfer path for engine firing frequency or a first order engine disturbance.

    5.

  5. If the mark placed on the face of an engine driven accessory seems to stand still while running this test, then that accessory system is either responding to an existing frequency; such as engine firing pulses, or creating a disturbance.

    6.

  6. A loose, damaged, misaligned, or defective engine driven accessory system insulator and/or bracket may create a transfer path into the passenger compartment.

    7.

  7. Removing the engine driven accessory and bracket(s) from the engine allows a thorough inspection to determine if any conditions are present that may create a transfer path into the passenger compartment.

Step

Action

Yes

No

1

Were you sent here from the Vibration Analysis - Engine table?

Go to Step 2

Go to Vibration Analysis - Engine

2

Inspect the powertrain mounts for the following:

  1. Loose and/or missing fasteners
  2. Improper alignment
  3. Cracked, dry-rotted, and/or oil-soaked insulators
  4. Twisted, broken, torn, and/or collapsed insulators
  5. Bent, twisted, and/or deformed brackets

Did any of the powertrain mounts exhibit any of the conditions listed?

Go to Step 3

Go to Step 4

3

Replace powertrain mounts as necessary. Refer to the following procedures:

    •  Engine Front Mount Replacement in Engine Mechanical - 7.8L
    •  Engine Rear Mount Replacement in Engine Mechanical - 7.8L
    • Transmission Mount Replacement in Manual Transmission - Medium Duty
    •  in Manual Transmission - ZFS6-650
    •  in Automatic Transmission - Allison

Did you complete the replacement?

Go to Step 12

--

4

Inspect the exhaust system components for the following:

    • Loose and/or missing fasteners
       - Heat Shields
       - Joints and/or couplings-nuts, bolts, studs, clamps, straps
       - Bracket and/or insulator mounting
    • Inadequate clearance to body and/or chassis components; with the exhaust system both COLD and HOT, in NEUTRAL, FORWARD and REVERSE gears
    • Improper alignment
    • Disconnected and/or missing insulators
    • Cracked, dry-rotted, and/or oil-soaked insulators
    • Stretched, twisted, broken, torn, and/or collapsed insulators
    • Bent, twisted, cracked, and/or deformed brackets

Did any of the exhaust systems components exhibit any of the conditions listed?

Go to Step 5

Go to Step 6

5

Repair, replace, and/or realign exhaust system components as necessary.

Did you complete the repair, replacement, and/or realignment?

Go to Step 12

--

6

Re-bed the powertrain:

  1. Loosen, but do not remove, all powertrain mounts and exhaust system hangers.
  2. Ensure that the exhaust flexible coupling, if equipped, moves freely.
  3. Start the engine.
  4. Settle the powertrain by shifting the transmission from DRIVE to REVERSE.
  5. Place the transmission into NEUTRAL.
  6. Turn OFF the ignition.
  7. Tighten all of the loosened fasteners with the powertrain in a relaxed position. Refer to the following procedures:
    8. •  Engine Front Mount Replacement in Engine Mechanical - 7.8L
    •  Engine Rear Mount Replacement in Engine Mechanical - 7.8L
    • Transmission Mount Replacement in Manual Transmission - Medium Duty
    •  in Manual Transmission - ZFS6-650
    •  in Automatic Transmission - Allison

Was the disturbance significantly reduced or eliminated?

Go to Step 12

Go to Step 7

7

Notice: Do not run the engine for longer than 60 seconds with the accessory drive belt, or belts removed, or overheating and/or damage may result.

  1. Remove the engine accessory drive belts.
  2. Block the front wheels.
  3. Apply BOTH the service brakes and the park brake.
  4. With the scan tool still installed, start the engine.
  5. Place the transmission in NEUTRAL or PARK.
  6. Increase the engine RPM to the level recorded during duplication of the disturbance.
  7. Allow the engine to idle, then place the transmission in DRIVE.
  8. Increase the engine RPM to the level recorded during duplication of the disturbance.
  9. Turn OFF the ignition.
  10. Install the engine accessory drive belts.

Was the disturbance significantly reduced or eliminated?

Go to Step 8

Go to Step 9

8

  1. Mark the face of the suspected accessory pulleys, including idler pulleys, if necessary, near the outer edge with a paint mark.
  2. Block the front wheels.
  3. Apply BOTH the service brakes and the park brake.
  4. With the scan tool still installed, start the engine.
  5. Have an assistant place the transmission in NEUTRAL.
  6. Slowly increase the engine RPM to the level recorded during duplication of the disturbance, then maintain that speed.
  7. Visually inspect each of the suspected accessory pulleys for lateral runout.

    8. Check each of the accessory systems, both engaged and under maximum load and disengaged or under minimum load.

  8. Allow the engine to idle and with the brakes still applied, place the transmission in DRIVE.
  9. Slowly increase the engine RPM to the level recorded during duplication of the disturbance, then maintain that speed closely.
  10. Visually inspect each of the suspected accessory pulleys for lateral runout.

    11. Check each of the accessory systems, both engaged and under maximum load and disengaged or under minimum load.

  11. Turn OFF the ignition.

Did you identify an engine driven accessory system as being related to the disturbance?

Go to Step 9

Go to Vibration Diagnostic Aids

9

Inspect the components of the engine driven accessory system for the following:

    • Loose and/or missing fasteners
       - Heat Shields, if equipped
       - Joints and/or couplings-nuts, bolts, studs, clamps, straps
       - Bracket and/or insulator mounting
    • Inadequate clearance to body and/or chassis components; with the accessory system both under a LOAD and NOT loaded
    • Improper alignment
    • Bent or damaged pulleys
    • Disconnected and/or missing insulators
    • Cracked, dry-rotted, and/or oil-soaked component insulators
    • Stretched, twisted, broken, torn, and/or collapsed component insulators
    • Bent, twisted, cracked and/or deformed component brackets

Did any of the components of the engine driven accessory system exhibit any of the conditions listed?

Go to Step 11

Go to Step 10

10

  1. Remove the engine driven accessory and brackets from the engine.
  2. Thoroughly inspect the accessory brackets, bolts/nuts/studs, and the accessory itself for signs of the following:

    3. Bent, twisted, cracked and/or deformed conditions

  3. Replace any of the components found to exhibit any of these conditions.
  4. Reinstall the components to the engine.

Did you find and correct a condition?

Go to Step 12

Go to Step 13

11

Repair, replace, and/or realign the engine driven accessory system components as necessary.

Did you complete the repair, replacement, and/or realignment?

Go to Step 12

--

12

Recheck the vehicle to determine if the disturbance is now significantly reduced or eliminated. Perform the following steps:

  1. Install a scan tool into the customer's vehicle.
  2. Block the front wheels.
  3. Apply BOTH the service brakes and the park brake.
  4. Start the engine.
  5. Place the transmission in NEUTRAL.
  6. Slowly increase the engine RPM to the level at which the disturbance was most noticeable.
  7. Visually inspect each of the suspected accessory pulleys for lateral runout.
  8. Place the transmission in DRIVE.
  9. Slowly increase the engine RPM to the level at which the disturbance was most noticeable.
  10. Visually inspect each of the suspected accessory pulleys for lateral runout.
  11. If the disturbance has been significantly reduced or eliminated, confirm the results by placing the transmission into REVERSE, then repeat steps 9 and 10.

Has the disturbance been significantly reduced or eliminated?

Go to Step 14

Go to Vibration Analysis - Engine Balance

13

Replace the engine driven accessory component causing the disturbance.

Did you complete the replacement?

Go to Step 14

--

14
  1. Install or connect any components that were removed or disconnected during diagnosis.
  2. Perform the Vibration Analysis - Road Testing table. Refer to Vibration Analysis - Road Testing .

Is the disturbance still present?

Go to Step 2

System OK