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What does a failed belt tensioner sound like?

Mike GMC

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Mike GMC Enthusiast

Mike GMC

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I'm trying to diagnose a tapping noise.  I strongly believe it is in the belt drive somewhere.  When I remove the belt, the noise goes away.  The noise also goes away when it's warm outside and once the engine warms up some.  The sound seems like a metal to metal tapping noise.  It's loud and is not rythmic but more random.  I thought I had it nailed down to the belt tensioner, but the replacement seems to be making the same noise.  Any ideas?

Mike GMC Enthusiast

Mike GMC

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Been trying that.  The only thing that seems to make the noise is the tensioner housing.

davester Senior Enthusiast

davester

Posted
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Is the belt tensioner within it's proper range (there should be an arrow on one part and a pair of marks on the other to indicate that it's in the right spot to provide the correct tension)?

 

Maybe examine the belt, there may be something on it?

kickass audio Enthusiast

kickass audio

Posted
Posted

Grab all of the pulleys on the drive belt system (engine off of course and not warm so you don't risk the fans coming on and catching your arms) and try to wiggle the pulleys up and down as well as side to side. Are they not moving around or wobbling? If so that's good. Next try to spin the pulley by hand and see how it feels in your hands, does it move smoothly or does it have times where it binds up or jumps in rotation? That would indicate a bad bearing. Does the noise get better or worse when your AC clutch kicks in and out? One final thought, check your tensioner to make sure that it doesn't have a loose pulley as well as where the single bolt goes through the tensioner to the block that it doesn't wobble around. The area that houses the spring has a rubber damper in it that stops rattling when the tensioner is working to take up slack in the belt but that shouldn't have failed for your age of the truck.

 

I know for me my drive belt loves to squeak after we get a cold night that warms up in the morning or if it rains the night before I start it up. It will continue squeaking until I get in and hit the throttle to drive and it dries the belt off. I have never experienced a tapping noise from a belt before.

diyer2 Senior Enthusiast

diyer2

Posted
Posted
36 minutes ago, davester said:

maybe use a mechanics stethoscope (carefully) to narrow down where the sound is coming from.

This is a must have for a DIYER.

Just recently helped a friend who had a squeak and couldn't locate it.

With my mechanics stethoscope found it in short order.

Idler pulley bearing was bad.

 

:)

Mike GMC Enthusiast

Mike GMC

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Ok, with the belt off, none of the pulleys seem like to have any issues.  At least none yet I can see or feel.  The stethoscope only seems to pick up the tapping sound when I put it on the tensioner housing.  The tension seems to be about tight according to the markings, it about in the middle.  Again, no noise with the belt off and engine on.  Turning the a\c on or off makes no difference.  It's definitely a tapping noise and not a squeak or squeel of any kind.  I'm at a bit of a lose.  I've replaced the tensioner based on where the stethoscope picked up the noise, but no change.  The weirdest part is the temperature dependence.  Why would it only happen when cold? 

Mike GMC Enthusiast

Mike GMC

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This engine does not have AFM.  Stethoscope does not pick up the noise anywhere on the valve covers, heads, timing cover, valley cover or block.  I picked up another tensioner and a new belt just to try.  I found out there are 2 belt lengths depending on which alternator you have.  The current belt is the shorter one, so I picked up the longer one just to try.  It's only about 3/4" difference in length.  I'll post back if either item fixes it.

Mike GMC Enthusiast

Mike GMC

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So far so good.  The new tensioner and the slightly longer belt seems to be working.  No noise so far, but it's not that cold today, mid 40's.  I'll fire it up tomorrow morning and see what happens.

Mike GMC Enthusiast

Mike GMC

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30 degrees this morning and no more noises.  Fingers crossed it doesn't come back.

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