Drive Belt Falls Off Diagnosis
Diagnostic Aids
If the drive belts repeatedly fall off the accessory drive pulleys, this may be caused by pulley misalignment.
If the drive belts repeatedly fall off the accessory drive pulleys, this may be caused by pulley misalignment.
If the drive belts are the incorrect length, the drive belt tensioners may not maintain the correct tension on the drive belts.
Test Description
The numbers below refer to the steps in the diagnostic table.
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This inspection is to verify the condition of the drive belts. Damage may have occurred to the drive belts when the drive belts fell off the pulley. Inspect the drive belts for cuts, tears, sections of ribs missing, or damaged belt plies.
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Misalignment of the accessory drive pulleys may be caused from incorrect mounting or incorrect installation of an accessory drive component, or the pulley may be bent inward or outward from a previous repair. Test for a misaligned pulley using a straight edge in the pulley grooves across 2 or 3 pulleys. If a misaligned pulley is found, refer to that accessory drive component for the correct removal and installation procedure of that pulley.
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Inspection of the accessory drive pulleys should include inspecting for bends, dents or other damage that May prevent the drive belt from seating correctly in the pulley grooves or on the smooth surface of a pulley when the back side of the drive belts are used to drive the pulley.
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Accessory drive component brackets that are bent or cracked will also cause the drive belts to fall off.
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Inspection of the fasteners can address the possibility that an incorrect bolt, nut, spacer, or washer was installed. Missing, loose, or incorrect fasteners may cause pulley misalignment from the accessory drive brackets moving under load. Over tightening the fasteners may cause misalignment of the accessory component brackets.
Step | Action | Yes | No |
|---|---|---|---|
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Notice: Refer to Belt Dressing Notice in the Preface section. DEFINITION: The drive belts fall off the pulleys or may not ride correctly on the pulleys. | |||
1 | Did you review the Symptoms - Engine Mechanical diagnostic information, and perform the necessary inspections? | Go to Step 2 | Go to Symptoms - Engine Mechanical . |
2 | Inspect the drive belts for wear, damage, debris build-up and missing drive belt ribs. Refer to Drive Belt Replacement - Accessory or Air Conditioning Compressor Belt Replacement . Was a damaged drive belt found? | Go to Step 3 | Go to Step 4 |
3 | Install new drive belts. Refer to Drive Belt Replacement - Accessory or Air Conditioning Compressor Belt Replacement . Do the drive belts continue to fall off? | Go to Step 4 | System OK |
4 | Inspect for misaligned drive pulleys. Did you find and correct the condition? | Go to Step 12 | Go to Step 5 |
5 | Inspect for a bent or dented accessory drive pulley. Did you find and correct the condition? | Go to Step 12 | Go to Step 6 |
6 | Inspect for a bent or a cracked accessory drive bracket. Did you find and correct the condition? | Go to Step 12 | Go to Step 7 |
7 | Inspect for incorrect, loose or missing fasteners. Were there any incorrect, loose and/or missing fasteners? | Go to Step 8 | Go to Step 9 |
8 |
Does the drive belt continue to fall off? | Go to Step 9 | System OK |
9 | Inspect the drive belt tensioner for correct operation. Refer to Drive Belt Tensioner Diagnosis . Does the drive belt tensioner operate correctly? | Go to Step 11 | Go to Step 10 |
10 | Replace the drive belt tensioner. Refer to Drive Belt Tensioner Replacement - Accessory or Drive Belt Tensioner Replacement - Air Conditioning . Does the drive belt continue to fall off? | Go to Step 11 | System OK |
11 | Inspect for a failed drive belt idler and drive belt tensioner pulley bearing. Refer to Drive Belt Tensioner Diagnosis . Did you find and repair the condition? | Go to Step 12 | -- |
12 | Run the engine in order to verify the repair. Does the drive belt still fall off? | -- | System OK |
Drive Belt Excessive Wear Diagnosis
Diagnostic Aids
Above acceptable wear on a drive belt is usually caused by incorrect installation or the wrong drive belts for the application.
Minor misalignment of the drive belt pulleys will not cause above acceptable wear, but will probably cause the drive belts to make a noise or to fall off the pulleys.
Major misalignment of the drive belt pulleys will cause above acceptable wear and may also make the drive belts fall off the pulleys.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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The inspection is to verify that the drive belts are correctly installed over all of the drive belt pulleys. Wear on the drive belts may be caused by misalignment the drive belts by one groove on a pulley.
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The installation of a drive belt that is to wide or to narrow will cause wear on the drive belts. The drive belt ribs should match all of the grooves on the pulleys.
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This inspection is to verify the drive belts is not contacting any parts 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 belts should not come in contact with an engine or a body component when snapping the throttle.
Step | Action | Yes | No |
|---|---|---|---|
|
Notice: Refer to Belt Dressing Notice in the Preface section. DEFINITION: Wear at the outside ribs of the drive belts due to an incorrectly installed drive belts | |||
1 | Did you review the Symptoms - Engine Mechanical diagnostic information and perform the necessary inspections? | Go to Step 2 | Go to Symptoms - Engine Mechanical . |
2 | Inspect the drive belts for the correct installation. Drive Belt Replacement - Accessory or Air Conditioning Compressor Belt Replacement . Did you find this condition? | Go to Step 5 | Go to Step 3 |
3 | Inspect for the correct drive belt. Did you find this condition? | Go to Step 5 | Go to Step 4 |
4 | Inspect for the drive belt rubbing against a bracket, hose, or wiring harness. Did you find and repair the condition? | Go to Step 6 | Go to Diagnostic Aids |
5 | Replace the drive belt. Refer to Drive Belt Replacement - Accessory or Air Conditioning Compressor Belt Replacement . Did you complete the replacement? | Go to Step 6 | -- |
6 | Run the engine in order to verify the repair. Is there still above acceptable drive belt wear? | -- | System OK |
