Alternator Decoupler Pulley

[deleted user]

Human hands caused that. If not some significant outside influence. Never seen one "jump" by itself.

regards
mech

[Eggman]

Never seen one "jump" by itself.

Many other designs have spring-loaded tensioner pulleys, unlike the Mirage belt tensioning design.

[deleted user]

Just another bearing to fail. Keep it simple, then the unnecessary parts are not there to fail.

regards
mech

[Eggman]

There are two potential scenarios at play here, according the the course of this discussion.
1. Either the belt jumped during the downshift, or
2. It was mispositioned by a mechanic.

I am not talking about the potential mechanics error, but the belt tension scenario. Do you suppose a spring-loaded tensioner pulley might possibly prevent a belt from jumping?

I do.

Just a thought. I wasn't there to watch it happen - it's all speculation.

[Eggman]

Also, the original post mentions that the symptoms (sound) started at downshift. I would think this marks the start of the problem, and thus clears the mechanic from fault.

[Daox]

I'm with Old Mech on this. I've had numerous cars without automatic tensioners and have never had any issues with them. I actually have had less issues with them than ones with auto tensioners.

[cyclopathic]

Could it be a fried tensioner? The noise on downshift could be explained by higher RPMs.

[Eggman]

Could it be a fried tensioner? The noise on downshift could be explained by higher RPMs.

What tensioner are you referring to?

[Eggman]

I'm with Old Mech on this. I've had numerous cars without automatic tensioners and have never had any issues with them. I actually have had less issues with them than ones with auto tensioners.

I totally understand what you are saying, and I also agree with Old Mech's sentiments that it is an unnecessary complication to be avoided. In another sense, I also agree with Old Mech when he says:

Human hands caused that.

and

Improper installation or retension. The belt really should need neither at that mileage.

But what if a automatic tensioner would help avoid something like this happening? It jumped at the downshift, indicating a tension problem.

Just speculating. Worth the cost of admission.

[deleted user]

Not one time in 30 years including everyone I knew in the industry did a belt spontaneously jump a groove.

regards
mech