Diagnostic Aids
If the drive belt repeatedly falls off the drive belt pulleys, this is a result of pulley misalignment.
An extra load that is quickly applied or released by an accessory drive component may cause the drive belt to fall off the pulley. Verify the accessory drive components operate properly.
If the drive belt is the incorrect length, the drive belt tensioner may not apply the proper tension on the drive belt.
Excessive wear on a drive belt is usually caused by an incorrect installation or the incorrect drive belt for the application.
Minor misalignment of the drive belt pulleys will not cause excessive wear, but will probably cause the drive belt to make a noise or to fall off.
Excessive misalignment of the drive belt pulleys will cause excessive wear but may also make the drive belt fall off.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This inspection is to verify the condition of the drive belt. Damage may have occurred to the drive belt when the drive belt fell off. The drive belt may be damaged, which caused the drive belt to fall off. Inspect the belt for cuts, tears, sections of ribs missing, or damaged belt plys.
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Misalignment of the pulleys may be caused from improper mounting of the accessory drive component, incorrect installation of the accessory drive component pulley, or the pulley being bent inward or outward from a previous repair. Test for a misaligned pulley using a straight edge in the pulley grooves across two or three pulleys. If a misaligned pulley is found refer to that accessory drive component for the proper repair procedure of that pulley.
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Inspecting the pulleys for being bent should include inspecting for a dent or other damage to the pulleys that would prevent the drive belt from not seating properly in all of the pulley grooves or on the smooth surface of a pulley when the back side of the belt is used to drive the pulley.
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Accessory drive component brackets that are bent or cracked may allow the drive belt to fall off.
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Inspecting of the fasteners can eliminate the possibility that a incorrect bolt, nut , spacer, or washer was installed. Missing, loose, or an incorrect fastener may cause pulley misalignment from the bracket moving under load. Over tightening of the fasteners may cause misalignment of the accessory component bracket.
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The inspection is to verify the drive belt is correctly installed on all of the drive belt pulleys. Wear on the drive belt may be caused by mis-positioning the drive belt by one groove on a pulley.
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The installation of a drive belt that is two wide or two narrow will cause wear on the drive belt. The drive belt ribs should match all of the grooves on all of the pulleys.
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This inspection is to verify the drive belt is not contacting any component of the engine or body while the engine is operating. There should be sufficient clearance when the drive belt accessory drive components load varies. The drive belt should not come in contact with an engine or a body component when snapping the throttle.
Step | Action | Yes | No | ||||
|---|---|---|---|---|---|---|---|
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Caution: Refer to Belt Dressing Caution in the Preface section. Definition
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1 | Did you review the symptoms-engine mechanical operation and perform the necessary inspections? | Go to Step 2 | Go to Symptoms - Engine Mechanical. | ||||
If diagnosing excessive wear, proceed to step 13. If diagnosing a drive belt that falls off, inspect for a damaged drive belt. Did you find the condition? | Go to Step 3 | Go to Step 4 | |||||
3 | Install a new drive belt. Does the drive belt continue to fall off? | Go to Step 4 | System OK | ||||
Inspect for pulley misalignment. Did you find and repair the condition? | Go to Step 12 | Go to Step 5 | |||||
Inspect for a bent or dented pulley. Did you find and repair the condition? | Go to Step 12 | Go to Step 6 | |||||
Inspect for a bent or a cracked accessory bracket. Did you find and repair the condition? | Go to Step 12 | Go to Step 7 | |||||
Inspect for improper, loose or missing fasteners. Did you find loose or missing fasteners? | Go to Step 8 | Go to Step 9 | |||||
8 |
Caution: Refer to Fastener Caution in the Preface section. Does the drive belt continue to fall off? | Go to Step 9 | System OK | ||||
9 | Inspect the drive belt tensioner for proper operation. Refer to Drive Belt Tensioner Diagnosis. Does the drive belt tensioner operate properly? | Go to Step 11 | Go to Step 10 | ||||
10 | Replace the drive belt tensioner. Does the drive belt continue to fall off? | Go to Step 11 | System OK | ||||
11 | Inspect for failed drive belt idler and/or drive belt tensioner pulley bearings. Did you find and repair the condition? | Go to Step 12 | Go to Diagnostic Aids | ||||
12 | Operate the system in order to verify the repair. Did you correct the condition? | System OK | Go to Step 2 | ||||
Inspect the drive belt for the proper installation. Did you find this condition? | Go to Step 16 | Go to Step 14 | |||||
Inspect for the proper drive belt. Did you find this condition? | Go to Step 16 | Go to Step 15 | |||||
Inspect the drive belt for contact against a bracket, hose, or wiring harness. Did you find and repair the condition? | Go to Step 17 | Go to Diagnostic Aids | |||||
16 | Replace the drive belt(s). Did you complete the replacement? | Go to Step 17 | -- | ||||
17 | Operate the system in order to verify the repair. Did you correct the condition? | System OK | -- | ||||
