How to tell if a belt tensioner is bad

[JHZR2]

Hi,

I need to know how to tell is an automatic belt tensioner is bad. I have a 98 S-10 ZR2 with the 4.3L V6. The other day, it started making a little bit different sound, and I came to the realization that the problem is actually the alternator bearings. The alt worked just fine, but the noise went away when I swapped it.

Now, I still hear some noise from the idler pulley and the belt tensioner. About the same noise level as when I put the stethoscope on the NEW alternator. All three parts are louder than the AC compressor, engaged or not.

That said, the noise is no longer audible int he cab, all is well, as it always was. But, how do I know when a belt tensioner is bad? Mine shakes some, especially when I hit the gas. However, it seems to me that such movement ought to be relatively normal, since the belt will flex somewhat with speed changes.

I think the tensioner also sometimes makes a ticking sound, just one or two ticks, a couple times, when Im accelerating from a stop. Usually its fine, though once in a while if the load increases substantially (like a hill comes up), Ill hear it again.

Similarly, how can I tell if the tensioner or idler pulley is going bad (bearings)? Will they make a grumbling noice? A squealing noise? I assume there is always some noise, especially on the hollow inside metal idler pulley. Do these pulleys go bad just out of the blue, or do you usually hear them in advance? Will they get real hot when theyre on the outs, since the bearings arent spinning efficiently?

Thanks very much for your help,

JMH

 

[Drew99GT]

It depends of what part of the tensioner is failing. They have a guage for spring tension; that'll tell you if you need to change it because it's making a belt squeeling noise from lack of tension. If it's making a loud whining noise, then the bearing on the pulley is probably getting tight. As far as the clicking noise, my Dad's 4.3L does the same thing, LOUDLY sometimes. He had the tensioner replaced, and the new one sounds identicle. It sounds like yours is fine. Oh, the shaking or movement of the tensioner as rpms increase is normal as well. Perhaps you should just slip the belt off the pully on the tensioner and spin it by hand to see how much friction you can feel.

 

[Chevynut67]

How many miles do you have on the truck? I have a '98 Blazer w/54K miles. I recently swapped out the belt tensioner after I noticed that it was getting a little cocked. Didn't want to risk it coming apart. I know someone that this happened to on a '97 Blazer. Check out daycoproducts.com for some info. on belts & tensioners.

 

[JHZR2]

My truck has 48k, and its been replaced before (Ive had the truck since new). Apparently the tensioners on these are a pretty weak item, and are a similar problem on the 350 v8 engines, as its used on that engine as well.

Thanks,

JMH

 

[Chevynut67]

I hope you're not using OEM replacemets. Mine was the original OEM & was made my Gates in Canada.

I replaced it with one from Dayco. It sems to be a beefier unit. I think it even had a lifetime warranty. Got it from AutoZone.

 

[JHZR2]

Yeah, the replacement I have is a dayco... Seems to still work, tension is fine. No lifetime warrantee on them from AZ around here. Got it at 25% off, since I also bought a goodyear gatorback belt.

JMH

 

[srivett]

I look for the belt flapping around, poor alignment, and a rough spinning movement when the belt is off. The CASE 580SuperL had a horrible tensioner, the belt would start flapping and get torn apart every thousand hours.

Steve

 

[wtd]

I have a 98 full size chevy with the 350 and its on its third tensioner. I think the one I just replaced was still good because the new one I put on was making the same knocking sound. I replaced the belt next and the sound is gone. Check your belt. When they get some miles on them, they stretch, and the tensioner doesn't seem to be able to compensate.

Wayne