Drive Belt Diagnosis
1. Observe the operation of the drive belt:
• If the belt has wear or faulty operation, go to step 2.
• If the belt makes excessive noise, go to step 3.
2. Check the drive belt system for faulty operation in the following steps:
A. Observe if the drive belt stays aligned with the pulleys during engine operation (see Figure 5-11):
• If the drive belt stays aligned with the pulleys, go to step B.
• If the drive belt becomes misaligned, check for the following conditions and make necessary repairs:
– Misaligned crankshaft or accessory pulleys
– Mispositioned or loose accessory support brackets
– Belt damage
– Faulty tensioner
– Worn idler or tensioner pulley bearings
B. Observe if the drive belt system causes excessive vibration during engine operation:
• If excessive vibration does not exist, go to step C.
• If excessive vibration exists, check for the following conditions and make necessary repairs:
– Bent or cracked pulleys
– Cracked, mispositioned or loose accessory support brackets
– Damaged cooling fan blades
– Worn or damaged water pump or cooling fan clutch
C. Check the drive belt for pilling (a random accumulation of rubber dust in the pulley grooves):
• If pilling fills the pulley grooves to a depth of less than 1/3, consider the amount of wear as normal and go to step D.
• If pilling fills the pulley grooves to a depth of more than 1/3, check the operation of the drive belt tensioner.
D. Check the drive belt for excessive wear on either outside rib:
• If no excessive wear exists, check the drive belt system for noisy operation.
• If excessive wear exists, replace the drive belt and check the match of the belt ribs to the pulley grooves.
3. Check the drive belt system for noisy operation in the following steps:
A. Listen for chirping (a high-pitched noise usually heard once per revolution of the belt or pulley):
• If no chirping noise exists, go to step B.
• If a chirping noise exists, check for the following conditions and make necessary repairs:
– Misaligned crankshaft or accessory pulleys
– Bent or cracked pulleys
– Mispositioned or loose accessory support brackets
– Belt damage
B. Listen for squealing (a loud screeching noise that is usually caused by a slipping belt, especially when the accessory load on the belt changes):
• If no squealing noise exists, go to step C.
• If a squealing noise exists, check for the following conditions and make necessary repairs:
– Seizing bearings in accessory components
– Low drive belt tension
– Excessive belt length (stretch)
C. Listen for whining (a high-pitched noise that is continuous):
• If no whining noise exists, go to step D.
• If a whining noise exists, check for the following conditions and make necessary repairs:
– Worn bearings in accessory components
– Bearing wear in the tensioner pulley or idler pulley
D. Listen for a faint, cycling, rumbling noise:
• If no noise is present, the drive belt system is working correctly.
• If the noise is present, clean pilling accumulation from pulley grooves and replace the drive belt.
