Belt Squeal Mystery - Need Help

5.0L Miata

Member
May 3, 2005
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Hey Everyone,

I have a 95GT with bolt-on's that I've been having accessory belt issues with for the past two seasons. Last summer the car was making a ticking noise which turned out to be a bad belt tensioner. I replaced it this winter with an aftermarket unit from Summit Racing.

This spring my first trip with the car it threw the belt off which I thought was really odd. It destroyed the belt in the process, so I purchased a new Goodyear Gatorback belt. I also noticed that the belt was riding on the front of the new tensioner pulley which I thought was maybe why the belt came off.

So I used a 1/4 spacer behind the tension to push it out so the belt rode on the middle of the pulley. The belt no longer flew off but now I had horrible belt squeal at startup and a slight chirping at idle. I figured maybe my spacer meant that the tension was not 100% straight and thus causing the squeal, so I went back to no spacer and the squeal is still here.

So three things come to mind now. One; my new belt could be glazed from the squealing and needs to be replaced again. Two; the aftermarket tensioner is crap and I should replace it with a Ford unit, or Three; I noticed a lot of rubber build-up around the alternator and perhaps my alternator is the cause? It is charging find and spins freely, but there is a lot of build up around it. Pictures attached to maybe help.

Thoughts?
 
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jozsefsz

5 Year Member
Aug 11, 2013
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Shimming the tensioner pulley should not cause any problems, I've had to do so before as well as not all aftermarket parts are created equal. I'd be surprised if that was rubber dust on the alternator, usually metal dust collects there due to magnetism.

If you're getting squealing, either the tensioner is inadequate, the belt is too long, or one of your accessories is binding. Remove the belt and spin each one by hand. The idler pulley, air pump, A/C, power steering, water pump, or alternator could be binding. They should all move absolutely freely, make no noise, have no spots where they 'stick', and have little if any free-play in any direction.
 

5.0L Miata

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Thanks for your response, I appreciate it. I had zero squealing issues last year before I replaced the tensioner. Ever since I installed it I have belt squeal and a thrown belt. My first instinct is to throw the $70 I just spent away and buy a $110 Ford tensioner (or an aftermarket piece that someone can recommend). Here is the Ford one on CJ Pony Parts: Ford Mustang Belt Tensioner W/ Pulley 5.0L 1994-1995

I am running a 90.2" belt. I have all stock accessories (including A/C) but no smog pump. I have spun all the accessories and they seem good. The only one that maybe suspect is the idler. It spins but maybe only two rotations by hand before it stops again. I'm wondering if it should spin more free than that?

Any other suggestions let me know.
 

jozsefsz

5 Year Member
Aug 11, 2013
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Usually when an idler is brand new it will spin a little tight, if it's well-worn it usually free-wheels pretty well. It may be worth a shot before you spend the money on a tensioner since they're pretty cheap. But it's hard to argue with the history you have -- if it was fine before, it's quite possible the tensioner isn't up to snuff. It's also important to check that the tensioner isn't bottoming out because the belt's loose. I also have a smog delete, and some brand belts seem quite a bit bigger than others. It should have some marks on it to tell you if you're within an acceptable range (the one you linked has two hash-marks on the top, between which the other one should sit when the belt is installed)..
 

toyman

SN Certified Technician
Jul 19, 2007
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I would remove the spacer to see if the squealing stops. If it does, you have the problem solved. The tensioner has a belt wear indicator on it. If the marker is in the good zone the belt length is okay. Also, using a soap bar, apply the soap to the belt to see if the squealing stops.
 

5.0L Miata

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May 3, 2005
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Thanks again for the responses. I have removed the spacer from the tensioner but the squeal continues. I am now getting a constant chirp as well that increases with the speed of the engine. I may try a new smaller belt to see if that helps. The aftermarket tensioner does not have a mark to indicate if it is in the right range, but I do see it on the original OE piece I still have.
 

jozsefsz

5 Year Member
Aug 11, 2013
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Awesome glad to hear it, that ticking you heard is actually the tensioner reaching its limit and bottoming out. No harm from it for a short time, and the proper length belt will keep that from happening again.