Knocking after replacing serpentine belt - tensioner jumps - 2008 Sequoia 5.7L

I put on a new belt as part of checking for some other issues I have had. When I start up there is a loud squeal for a second then it goes away but a knock starts up and persists.

I can see the belt tensioner jump with every knock. So something is putting extra pressure on the tensioner and making the noise. You can see the tensioner jumping in the video I linked below.

I took off the belt and hand turned every pulley, everything turns easily except the crank. No wobble detected on anything, no rubbing detected. Anyone have experience with this?

Here is a link to the video, so you can see/hear it for yourself. What do you think I should look at first?

https://youtube.com/shorts/unV_nrpRxNw?si=WwYFOKyePZvtkQxG

 

I removed the belt completely and yanked on all of the pulleys and cannot seem to find anything that looks like it’s loose or out of alignment or grinding. Has anybody seen anything like this before?

 

Ever replace that tensioner?

 

I have not replaced the tensioner is that something that’s commonly needed?

I thought about that, but it’s very stiff. It seems to be holding in place when it’s not turning and it doesn’t seem like the bearing has any problem in it.

 

Typically gets replaced with every belt change. I just had to replace one on my Mom's 2008 Focus. Had never been done and the belt kept slipping off. Car was making all sorts of noise and now it's pretty quiet.

 

Yes, springs weaken in the tensioner requiring replacement- but I’m not 100% that’s your issue. Usually the belt will squeak or chirp when a tensioner is failing - not straight to jumping.

 

You’re absolutely sure it’s routed correctly?

 

it’s cheap enough. I’ll give it a try and I’ll let you know. Thanks for the suggestion!

 

It follows the diagram that I found online and in my Haynes manual. I can’t see any other way that it could potentially be put on and maintain tension.

 

In the Focus' case there wasn't any belt squeak or chirp. A lot of the noise came from that pulley. I also felt that it was pretty tension-y but that was by hand - apparently it wasn't remotely holding the tension it should have when a load is applied on it via power steering, etc.

 

Swapped the tensioner, and took care of the issue. Thanks alot!