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

Test Description

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

  1. If sufficient clearance exists to separate the transmission torque converter from the engine flywheel/flexplate, then further tests can be used to isolate the transmission from the engine.

    2.

  2. An engine flywheel/flexplate that has excessive lateral runout, when combined with the mass of the transmission torque converter, can produce a disturbance.

    3.

  3. An engine flywheel/flexplate that is loose at the engine crankshaft or that is cracked or damaged, when combined with the mass of the transmission torque converter, can produce a disturbance.

    4.

  4. This step is designed to isolate the transmission from the engine to determine if the disturbance is related to the engine ONLY.

    5.

  5. Re-indexing the transmission torque converter to the engine flywheel/flexplate alters the balance relationship between the torque converter and the rear of the engine.

    6.

  6. An engine flywheel that has excessive lateral runout, when combined with the extra mass of the clutch pressure plate and clutch driven plate, can produce a disturbance.

    7.

  7. The clutch pressure plate and the engine flywheel are marked for proper indexing of the heavy-spot of one to the light-spot of the other. Improper indexing of the pressure plate to the flywheel can produce a disturbance.

    8.

  8. An engine flywheel that is loose at the engine crankshaft or that is cracked, damaged and/or missing balance weights; and/or a clutch pressure plate and clutch driven plate that has loose springs, cracks, warpage, damage and/or missing balance weights -- when their mass is combined, can produce a disturbance.

    9.

  9. An engine flywheel that is loose at the engine crankshaft or that is cracked, damaged and/or missing balance weights; and/or a clutch pressure plate and clutch driven plate that has loose springs, cracks, warpage, damage and/or missing balance weights -- when their mass is combined, can produce a disturbance.

    10.

  10. Re-indexing the pressure plate to the engine flywheel alters the balance relationship between the pressure plate/flywheel assembly and the rear of the engine.

    11.

  11. An engine flywheel/flexplate that is damaged, misaligned, and/or imbalanced, can produce a disturbance.

    12.

  12. An engine crankshaft (harmonic) balancer that is damaged, misaligned, and/or imbalanced, can produce a disturbance.

Step

Action

Yes

No

1

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

Go to Step 2

Go to Vibration Analysis - Engine/Accessory Isolation

2

Is the vehicle equipped with a manual transmission?

Go to Step 10

Go to Step 3

3

  1. Secure the vehicle for testing:
    2. • Fully apply the park brake
    • Block the drive wheels
    • Place the transmission in NEUTRAL
  2. Remove the flywheel/flexplate-to-torque converter access cover bolts, if equipped.
  3. Determine if sufficient clearance exists to separate the transmission torque converter away from the engine flywheel/flexplate and safely secure the torque converter from accidentally engaging with the flywheel/flexplate.

Is there sufficient clearance to separate and safely secure the transmission torque converter away from the engine flywheel/flexplate?

Go to Step 4

Go to Step 10

4

  1. With the flywheel/flexplate-to-torque converter access cover still removed, mark the position of the transmission torque converter in relation to the engine flywheel/flexplate.
  2. Disconnect the torque converter and move it away from the flywheel/flexplate.
  3. Secure the transmission torque converter away from the engine flywheel/flexplate.
  4. Start the engine and allow the engine to idle.
  5. Visually inspect the flywheel/flexplate for excessive lateral runout.
  6. Turn OFF the ignition.

Did the flywheel/flexplate exhibit excessive lateral runout?

Go to Step 7

Go to Step 5

5

Inspect the flywheel/flexplate for the following:

  1. Looseness at the engine crankshaft
  2. Cracks and/or damage
  3. Missing balance weights

Did the flywheel/flexplate exhibit any of the conditions listed?

Go to Step 7

Go to Step 6 x

6

  1. Tie the transmission torque converter away from the engine flywheel/flexplate to avoid accidental engagement with the flywheel/flexplate.
  2. Apply BOTH the service brakes and the park brake.
  3. With the scan tool still installed, start the engine.
  4. Place the transmission in NEUTRAL or PARK.
  5. Slowly increase the engine speed (RPM) to the level at which the disturbance is most noticeable.
  6. Record the engine RPM obtained on the scan tool.
  7. Turn OFF the ignition.

Has the disturbance been significantly reduced or eliminated?

Go to Step 8

Go to Step 10

7
  1. If the flywheel/flexplate is loose at the engine crankshaft, tighten the flywheel/flexplate mounting bolts in sequence and to specification.
  2. If the flywheel/flexplate is cracked, damaged, and/or has missing balance weights, replace the damaged flywheel/flexplate.

Refer to Engine Flywheel Replacement in Engine Mechanical - 7.8L.

Did you complete the tightening or replacement?

Go to Step 23

--

8

  1. Re-index the transmission torque converter to the engine flywheel/flexplate, 120 degrees from its original position.
  2. Reconnect the transmission torque converter to the engine flywheel/flexplate.
  3. Apply BOTH the service brakes and the park brake.
  4. With the scan tool still installed, start the engine.
  5. Ensure the transmission is in NEUTRAL or PARK.
  6. Slowly increase the engine speed (RPM) to the level at which the disturbance is most noticeable.
  7. Record the engine RPM obtained on the scan tool.
  8. If the disturbance is still noticeable, re-index the torque converter again to obtain the least amount of disturbance.

Has the disturbance been significantly reduced or eliminated?

Go to Step 23

Go to Step 9

9

Replace the out-of-balance transmission torque converter.

Did you complete the replacement?

Go to Step 23

--

10

  1. Secure the vehicle for testing:
    2. • Fully apply the park brake
    • Block the drive wheels
    • Place the transmission in NEUTRAL
  2. With the engine running, visually inspect the crankshaft balancer/crankshaft pulley for excessive lateral runout

Does the crankshaft balancer/crankshaft pulley appear to have excessive lateral runout?

Go to Step 21

Go to Step 11

11

Is the vehicle equipped with an automatic transmission?

Go to Step 17

Go to Step 12

12

  1. Remove the flywheel inspection cover.
  2. Start the engine and slowly increase engine speed until the engine runs smoothly.
  3. Visually inspect the engine flywheel clutch surface for excessive lateral runout.

Does the engine flywheel clutch surface exhibit excessive lateral runout?

Go to Step 19

Go to Step 13

13

Inspect the clutch pressure plate to engine flywheel mounting for proper factory indexing. Refer to Clutch Assembly Replacement in Clutch or

Is the clutch pressure plate properly indexed to the engine flywheel?

Go to Step 15

Go to Step 14

14

  1. Remove the clutch pressure plate and clutch driven plate from the engine flywheel. Refer to Clutch Assembly Replacement in Clutch.
  2. Inspect the engine flywheel for the following:
    3. • Looseness at the engine crankshaft
    • Cracks, warpage and/or damage
    • Missing balance weights
  3. Inspect the clutch pressure plate and clutch driven plate for the following:
    4. • Loose and/or damaged clutch driven plate damper springs
    • Loose and/or damaged clutch pressure plate diaphragm springs
    • Cracks, warpage and/or damage
    • Missing balance weights

Do any of the above conditions exist?

Go to Step 18

Go to Step 16

15

  1. Remove the clutch pressure plate and clutch driven plate from the engine flywheel. Refer to Clutch Assembly Replacement in Clutch.
  2. Inspect the engine flywheel for the following:
    3. • Looseness at the engine crankshaft
    • Cracks, warpage and/or damage
    • Missing balance weights
  3. Inspect the clutch pressure plate and clutch driven plate for the following:
    4. • Loose and/or damaged clutch driven plate damper springs
    • Loose and/or damaged clutch pressure plate diaphragm springs
    • Cracks, warpage and/or damage
    • Missing balance weights

Do any of the above conditions exist?

Go to Step 18

Go to Vibration Diagnostic Aids

16

Re-index the pressure plate to the engine flywheel.

Did you complete the re-indexing?

Go to Step 23

--

17

Replace the imbalanced engine flywheel/flexplate. Refer to Engine Flywheel Replacement in Engine Mechanical - 7.8L.

Did you complete the replacement?

Go to Step 23

--

18

Replace the clutch pressure plate and clutch driven plate. Refer to Clutch Assembly Replacement in Clutch.

Did you complete the replacement?

Go to Step 23

--

19

  1. Loosen the flywheel to crankshaft bolts and retighten according to the proper sequence and specification. Refer to Engine Flywheel Replacement in Engine Mechanical - 7.8L.
  2. Start the engine; apply the throttle slightly until the engine runs smooth.
  3. Visually inspect the engine flywheel clutch surface for excessive lateral runout.

Is excessive lateral runout still present?

Go to Step 20

Go to Step 23

20

Replace the engine flywheel. Refer to Engine Flywheel Replacement in Engine Mechanical - 7.8L.

Did you complete the replacement?

Go to Step 23

--

21

    • Torque the crankshaft balancer to the proper specification. Refer to Crankshaft Balancer Replacement in Engine Mechanical - 7.8L.
    • With the engine running, visually inspect the crankshaft balancer/crankshaft pulley for excessive lateral runout

Has the disturbance been significantly reduced or eliminated?

Go to Step 23

Go to Step 22

22

Replace the engine crankshaft (harmonic) balancer. Refer to Crankshaft Balancer Replacement in Engine Mechanical - 7.8L.

Did you complete the replacement?

Go to Step 23

--

23
  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 Vibration Diagnostic Aids

System OK