I recently replaced my main serpentine belt (99 C-5)and at the same time replace the tensioner pulley and AC belt. I have now "thrown" the belt twice. Once was while under full power and now just under normal driving conditions. Any ideas? The belt looks OK and there seems to be plenty of tension. I am puzzled.

 

One of the pulleys somewhere is just slightly out-of-plane (alignment) and the belt wants to pull itself up on that pulley rim and then throw itself off. You might want to look at each of the pulleys and see if there are any more marks on the edge of a spcific pulley than on other pulleys. I would look where the back of the belt runs on pulleys (I haven't looked at the pulley path).

Good luck

 

When I watch the crankshaft pulley, it almost appears to "wobble". I have seen other cars and they are similar though

 

Look at the Crank Pulley. I bet the rubber is started to seperate between the two pcs. I had tha same happen to me right after my blower install and ECS sent me a good balancer.

Shahram

 

I had the wobble on the crank & it threw the belt. The cure is a new dampner. The rubber sleve is starting to seperate from the inner hub.

 

Unfortunately, this happens too often to SCCA T1 drivers... including myself. If the bearings start to go out on one of the driven components, then the above described misalignment can occur. I would check the alternator and power steering pumps for axial play in the shafts that could cause your problem along with the other things mentioned in the thread.

 

Document ID# 600040
2000 Chevrolet/Geo Corvette


--------------------------------------------------------------------------------

Drive Belt Falls Off Diagnosis
Diagnostic Aids
If the drive belt(s) repeatedly falls off the drive belt pulleys, this may be caused by pulley misalignment.

An extra load that is quickly applied or released by an accessory drive component may cause the drive belt(s) to fall off the pulleys. Verify that the accessory drive components operate properly.

If the drive belt(s) is the incorrect length, the drive belt tensioner may not maintain the proper tension on the drive belt.

Test Description
The number(s) below refer to the step number(s) on the diagnostic table.

This inspection is to verify the condition of the drive belt(s). Damage may have occurred to the drive belt when the drive belt(s) fell off the pulley. The drive belt(s) may have been damaged in which case caused the drive belt to fall off the pulley. Inspect the drive belt(s) for cuts, tears, sections of ribs missing, or damaged belt plys.

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 is 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 installation procedure of that pulley.

Inspect the pulleys for dents, bends or other damage. Damage to the pulleys would prevent the drive belt(s) from seating properly in the pulley grooves. Damage would also prevent proper alignment of the drive belt to pulley, when the smooth surface of the drive belt is required to drive the pulley.

Accessory drive component brackets that are bent or cracked will allow the drive belt(s) to fall off the pulley.

Inspection of the fasteners can eliminate the possibility that a wrong bolt, nut, spacer, or washer was installed. Missing, loose, or incorrect fasteners may cause pulley misalignment from the bracket moving under load. Over tightening of the fasteners may also cause misalignment of the accessory component bracket.

Step
Action
Yes
No


Notice
Do not use belt dressing on the drive belt. Belt dressing causes the breakdown of the composition of the drive belt. Failure to follow this recommendation will damage the drive belt.


DEFINITION: The drive belt falls off the pulleys or may not ride correctly on the pulleys.

1
Did you review the Symptoms - Drive Belt diagnostic information and perform the necessary inspections?
Go to Step 2
Go to Symptoms - Drive Belt

2
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. Refer to Drive Belt Replacement - Accessory or Drive Belt Replacement - Air Conditioning .

Does the drive belt continue to fall off?
Go to Step 4
System OK

4
Inspect for misalignment of the pulleys.

Did you find and repair the condition?
Go to Step 12
Go to Step 5

5
Inspect for a bent or dented pulley.

Did you find and repair the condition?
Go to Step 12
Go to Step 6

6
Inspect for a bent or a cracked bracket.

Did you find and repair the condition?
Go to Step 12
Go to Step 7

7
Inspect for improper, missing or loose fasteners.

Did you find loose or missing fasteners?
Go to Step 8
Go to Step 9

8
Tighten any loose fasteners. Refer to Fastener Tightening Specifications .

Replace improper or missing fasteners.

Does the drive belt continue to fall off?
Go to Step 9
System OK

9
Test the drive belt tensioner for operating correctly. 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 Replacement - Accessory or Drive Belt Replacement - Air Conditioning .

Does the drive belt continue to fall off?
Go to Step 11
System OK

11
Inspect for failed drive belt idler and drive belt tensioner pulley bearings.

Did you find and repair the condition?
Go to Step 12
Go to Diagnostic Aids

12
Run the engine in order to verify the repair.

Does the drive blet still fall off?
System OK

 

I had this happen to me on my mother-in-law's Buick LeSabre. I'd put the belt back on and it would come off within a mile.

Turns out the belt was saturated with engine coolant that was seeping out on cool down. It wasn't noticed at first because the belt soaked it up like a sponge.

Fixed the leak, replaced the belt. Problem gone.

Just another suggestion from left field.

 

Alignment. Make sure the balancer isn't coming off. It happens to LS1's.

 

Check the bolt on the harmonic balancer. It might be loose and throwing the belt. This is very common and a Bi*%h to change (if you do it yourself).

 

That is your problem I would bet. The LS1 balancers have a rubber isolator between the inner and outer parts of the pulley. When the rubber begins to deteriorate, the balancer starts to wobble. When you are going through the different rpm's the wobble get's bad enough to throw the belt off the channel. I would bet you need a new pulley. There was a suggestion to check the bolt. I would do that quickly because if it is loose it could work it's way out and cause damage to the steering rack, front seal, front cover, etc.