Lash in alternator pulley normal? Newer 5.3L

[BLUE72CAMARO]

So a buddy of mine has a 15 Sierra that is actually my dads old truck. He has a mystery high pitch not very loud squeal coming from the passenger side of the engine it seems. So last night he brought it out and we threw it on the lift and started looking things over. I pulled the main serpentine belt to check bearings on the idler and other accessories. I never found the source of the sound but I am curious as to why the alternator pulley would have what feels like lash in a gearbox when changing direction of rotation. Its not a ton but probably a degree or two of clunk in the pulley before it turns the shaft the other way but it has no axial end play in it....

Anybody know whats going on with it or why it has this?

 

[gramps]

It’s clutched. Only spins the alternator one direction - lets it freewheel when you mash the go pedal.

 

[BLUE72CAMARO]

Looks like a test of locking up the alternator with a screw driver to test the pulley is in order then as when reversing the alternator back and forth by hand it was clunking both ways but never seemed to slip either direction.

 

[badazz81z28]

Hmm, I have never noticed it any of my LS engine. They all seem to spin smoothly like I would think alternator would.

 

[camarochevy1970]

There is something to the truck alternators, where the ECU can disengage them when the battery it topped off to save on fuel. I would not be surprised if that is what you are feeling.

 

[McCune]

It’s clutched. Only spins the alternator one direction - lets it freewheel when you mash the go pedal.

It is a decoupler and it freewheels when the throttle it lifted not mashed.

 

[McCune]

There is something to the truck alternators, where the ECU can disengage them when the battery it topped off to save on fuel. I would not be surprised if that is what you are feeling.

Nothing you could feel, it is electronically controlled not mechanically.

 

[Knuckle Dragger]

Picture of the pulley would clear up the clutch non clutch discussion. The new Tahoes are clutched.

 

[McCune]

The 2015 Sierra uses a decoupling pulley, it is for smother operation of the belt tensioner ( less noise).

 

[BLUE72CAMARO]

Yep McCune is right on all accounts. I am betting this thing is toast but I will find out tonight.

This is what it looks like