When I got my '86 GT several years ago, I soon got sick of the alternator belt squealing everytime it rained. Sure, I could tighten the belt, but that was always a temporary repair as two weeks later it would squeal again. I bought Dodgerunner's auto belt tensioner and was very happy with it. Solved the problem completely. The belt never squealed again.

Fast-forward... and a month or so ago I acquired an '88 Formula. I want to sell the 86 GT, so I figured I'd transfer the belt tensioner over to the Formula. I noticed the pulley on the Formula's alternator had an extra rib, but after researching here, I learned that installing the belt towards the inner ribs on the alternator would work fine in regards to belt alignment.

However, I noticed something just didn't seem right when I installed the alternator belt on the Formula. It seemed like the auto tensioner pulley was closer to the crank pulley than what I remembered on the GT. There was very little space between the two pulleys. It was almost like the belt was now too long.

And then a couple weeks later, the belt started squealing! What the heck...!

Anyway, to make a long story short, I discovered that not only was there an extra rib on the Formula's alternator pulley, but also that the diameter of the Formula's pulley was smaller (2 3/8") than the one on the GT (2 5/8").

These pictures will show the difference.




The top pulley is flipped over so that the pulleys are sitting outer end to outer end.



I now have a larger pulley installed (taken off a junk alternator I had sitting around) with the correct number of ribs. The larger alternator pulley will result in less drag on the engine (alternator still charges just fine, even at idle), and the replacement pulley is much lighter as well. (Different type of construction.) It was a win-win situation to replace this pulley.

And the belt doesn't squeal anymore!

Small pulley has less belt contact and makes Alt RPM higher.

Yes, I've said in past that squealing belts are symptom of other problem.
Wrong alt pulley is one.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

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quote Originally posted by Patrick: I noticed something just didn't seem right when I installed the alternator belt on the Formula. It seemed like the auto tensioner pulley was closer to the crank pulley than what I remembered on the GT. There was very little space between the two pulleys. It was almost like the belt was now too long.

Thought I should post this image from Dodgerunner's thread to show how the belt tensioner is installed on a 2.8 and why it would be a problem to have the tensioner pulley arm rotated too close to the crank pulley. (The auto belt tensioner would be at the end of its travel and no longer able to take up the slack of the belt.)

[This message has been edited by Patrick (edited 10-06-2013).]

I've frequently found that aftermarket alternators for a particular application will have a different pulley. I guess it's because the alternator is used on a number of vehicles. My wife's Grand Am went through at least a half-dozen alternators in it's 300K mile lifetime. They should have had 5-rib pulleys, but most came with a 4-rib pulley. Even with the correct number of ribs, the pulleys also varied in diameter. Usually smaller than the original. After I learned about the differences, I just had the parts store swap pulleys before I left the store.

In the pics that you posted, the smaller pulley is one that I usually see installed on 4 cylinder alternators. The larger one is installed on the V6 alternators.
Talking specifically about 88 Fieros.

quote Originally posted by fierofool: Even with the correct number of ribs, the pulleys also varied in diameter. Usually smaller than the original.

quote Originally posted by Raydar: ...the smaller pulley is one that I usually see installed on 4 cylinder alternators. The larger one is installed on the V6 alternators.

Yes, the alternator on the Formula is a rebuilt one (I can tell by the label on it), so I guess that explains why the wrong pulley was on it.

Ya can't assume anything is correct these days!