4.0 V6 Harmonic Balancer questions | Ford Explorer Forums - Serious Explorations

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4.0 V6 Harmonic Balancer questions

Cobra Jet

Well-Known Member
April 11, 2006
Reaction score
City, State
Southern, NJ
Year, Model & Trim Level
2004 XLS
First, yes, I have completed a "search" of the subject and have read every single thread as well (all of which are very informative) pertaining to "harmonic balancer" for the 4.0 engine...

I just have one question that I have not seen posted in any of those threads w/ regards to a failing 4.0 harmonic balancer:

Will the balancer only squeal or squeak when it is under load (meaning, when the serpentine belt is ON)?

The reason I ask is, I have already PREVIOUSLY replaced (due to wear):

belt tensioner assembly
idler pulley

Now I am getting the famous "squeal" at idle & while driving - but, when I remove the serpentine from the front accessories and start the engine w/ no belt - I don't get any squeal at all.

The other accessory drive pulleys (water pump, A/C, P/S & Alt) do not make any bearing or other noises when spun manually w/ the belt off (nor do I hear any noises coming from them when the truck is running).

I also see a slight "bobbing" of the belt tensioner when the truck is running @ idle (and belt is on).

I've replaced my harmonic balancer or so the stealership said so. The squeek has returned now at 175K. My harmonic balancer is now squeeking again. It seems to squeek mostly during acceleration and then rythmically.


I replaced my balancer today after this awful squeal under the hood and was tracked down to this.The belt slipped off the pulley and was running on the blacer itself. ( don't ask me how) Very common problem from what I gather here. I replaced this after replacing my belt, tensioner. I do know from alot of help here that there should be no play in any pulley. Help you any?

The balancer is a solid object that should make no noise ever.The only thing which touches it besides the belt is the front seal, that should be a rubber on oiled shaft quiet joint. There is a plastic dust shield next to the seal surface to lessen dirt reaching the seal area, but it should not touch anything.

I'd look elsewhere for the noise. Try the cam sensor, which is just like a distributor in that it has bearing which do wear out and squeal. It's down the center of the engine, on the top, front or rear of the block. That is more likely to make noise, and that would be any time the engine runs. Good luck,