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Accessory drive belt diagnosis

VISUAL DIAGNOSIS

When diagnosing serpentine accessory drive belts, small cracks that run across the ribbed surface of the belt from rib to rib (Fig. 16), are considered normal.

These are not a reason to replace the belt. However, cracks running along a rib (not across) are not normal.

Any belt with cracks running along a rib must be replaced (Fig. 16). Also replace the belt if it has excessive wear, frayed cords or severe glazing.

Refer to the Accessory Drive Belt Diagnosis charts for further belt diagnosis.

Fig. 16 Belt Wear Patterns
Fig. 16 Belt Wear Patterns

1 - NORMAL CRACKS BELT OK
2 - NOT NORMAL CRACKS REPLACE BELT

NOISE DIAGNOSIS

Noises generated by the accessory drive belt are most noticeable at idle. Before replacing a belt to resolve a noise condition, inspect all of the accessory drive pulleys for alignment, glazing, or excessive end play.

ACCESSORY DRIVE BELT DIAGNOSIS CHART

CONDITION

POSSIBLE CAUSES

CORRECTION
RIB CHUNKING (One or more ribs has separated from belt body)
  1. Foreign objects imbedded in pulley grooves.
  2. Installation damage
  1.  Remove foreign objects from pulley grooves. Replace belt.
  2. Replace belt
RIB OR BELT WEAR
  1. Pulley misaligned
  2.  Abrasive environment
  3.  Rusted pulley(s)
  4. Sharp or jagged pulley groove tips
  5. Belt rubber deteriorated
  1. Align pulley(s)
  2. Clean pulley(s). Replace belt if necessary
  3. Clean rust from pulley(s)
  4.  Replace pulley. Inspect belt.
  5. Replace belt
BELT SLIPS
  1. Belt slipping because of insufficient tension
  2.  Belt or pulley exposed to substance that has reduced friction (belt dressing, oil, ethylene glycol)
  3. Driven component bearing failure (seizure)
  4.  Belt glazed or hardened from heat and excessive slippage
  1.  Adjust tension (2.5L)
  2.  Replace belt and clean pulleys
  3.  Replace faulty component or bearing
  4.  Replace belt.
LONGITUDAL BELT CRACKING
  1. Belt has mistracked from pulley groove
  2. Pulley groove tip has worn away rubber to tensile member
  1.  Replace belt
  2.  Replace belt
9GROOVE JUMPING" (Belt does not maintain correct position on pulley)
  1. Belt tension either too low or too high
  2.  Pulley(s) not within design tolerance
  3.  Foreign object(s) in grooves
  4.  Pulley misalignment 4. Align component
  5.  Belt cordline is broken
  1.  Adjust belt tension (2.5L)
  2.  Replace pulley(s)
  3. Remove foreign objects from grooves
  4.  Replace belt
BELT BROKEN (Note: Identify and correct problem before new belt is installed)
  1. Excessive tension
  2. Tensile member damaged during belt installation
  3. Severe misalignment
  4.  Bracket, pulley, or bearing failure
  1.  Replace belt and adjust tension to specification
  2.  Replace belt
  3.  Align pulley(s)
  4. Replace defective component and belt
NOISE (Objectionable squeal, squeak, or rumble is heard or felt while drive belt is in operation)
  1. Belt slippage
  2.  Bearing noise
  3.  Belt misalignment
  4.  Belt to pulley mismatch 4. Install correct belt
  5.  Driven component induced vibration
  6.  System resonant frequency induced vibration
  1. Adjust belt tension (2.5L)
  2. Locate and repair
  3.  Align belt/pulley(s)
  4. Locate defective driven component and repair
  5.  Vary belt tension within specifications.
TENSION SHEETING FABRIC FAILURE (Woven fabric on outside, circumference of belt has cracked or separated from body of belt)
  1. Tension sheeting contacting stationary object
  2.  Excessive heat causing woven fabric to age
  3.  Tension sheeting splice has fractured
  1.  Correct rubbing condition
  2.  Replace belt
  3.  Replace belt
CORD EDGE FAILURE (Tensile member exposed at edges of belt or separated from belt body)
  1. Excessive tension
  2.  Belt contacting stationary object
  3.  Pulley(s) out of tolerance
  4.  Insufficient adhesion between tensile member and rubber matrix
  1.  Adjust belt tension (2.5L)
  2.  Replace belt
  3.  Replace pulley
  4.  Replace belt and adjust tension to specifications
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