Belt Tension - Second Generation Pontiac Firebird (1970 - 1981) - Firebird Nation

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Belt Tension


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#1 aw9d

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Posted 07 February 2020 - 09:52 AM

I'm sure it's been answered but I just can't find it while searching. How tense do the belts need to be? I have three issues I'm fighting right now and I keep messing with belt tension but nothing seems to fix them. 

 

Issue 1: Belt squeal around 3k rpm and up (sometimes starts around 2500 rpm depending on how much throttle you are giving it). Belt dressing helps but it's temporary as the next day it will squeal again. I've sanded down the pulleys with 180 grit sand paper. I didn't go nuts on it so maybe more would help? Or more gritty sand paper? 

 

Issue 2: Whine. Sounds like I have super charger whine almost and is non-stop but gets louder under acceleration. I'm guessing this has to do with belt tension or possible issue #3 below? 

 

Issue 3: Alternator pulley isn't lining up correctly. I got an AC-Del-co alternator, which was what was on the car. But the pulley doesn't line up with the new alternator. The pulley looked different and I'm wondering if my father-in-law had some alternative pulley that I should of kept but didn't.  I've added some washers to the brackets but still it's off a bit. I even added a waster to the fan on the alternator to space it out a bit as well but I'm still off. Should I look into a different pulley for the alternator? I am unsure to what has changed as it did line up before the engine was pulled/rebuilt with the old alternator which as the same part number as the one I have now. 

 

The pic looks like it's too far out towards the radiator but if you look at the pulley on the water pump it's riding the inside edge closer to the motor. The two pulleys don't line up, about 1/8th inch off. I'll try to get better pics later today. 

 

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#2 JOE68

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Posted 07 February 2020 - 04:22 PM

you should be able to flex the belt about a half inch with your finger.     the front belt is riding low in the pulley....prob worn ...try a new one



#3 myk74

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Posted 07 February 2020 - 04:37 PM

I don't think that washer/spacer is supposed to be there



#4 sea dog

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Posted 08 February 2020 - 04:45 AM

Having a belt out of line is a sure way to get belt squeal, quick belt wear, and a belt that gets ate up & breaks.

 

Rebuilding companies hire unqualified workers to do the job. Find an exploded parts diagram for your 71 bird. Then remove pulley nut and see if any washers, spacers, etc have been added or left off the pulley / fan assembly of alt.

 

Even though GM alts of the period are stand size units, see if new alt is the same amp rating as what came on car. An old Motor's, or Clinton big book will have alr specs.

 

If your new alt is 70 amps or more, the alt you received is in a different class than original. And it may be a different depth than original alt. This would alter pulley line up.



#5 aw9d

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Posted 10 February 2020 - 11:36 AM

Thanks for the replies. Sorry for the late reply, I had to take down a few Mesquite trees this weekend and it kicked my ass. 

 

As for the washers, they shouldn't be there. I'm trying what I can to get it the alternator to line up correctly. Without the washers the alignment is really off. With the washers I'm close, but not perfect. 

 

The belts are brand new and I've been messing with tension a bit more. I'm going to order a tension gauge and see if that helps. 

 

Rebuilding was done by my mechanic who has done a few of my motors in the past. I did help with a lot of the rebuild process and nothing was really changed out. I'll go back and double check this weekend to make sure everything is matching an exploded diagram. All other belts are lining up perfectly, just this alternator one is off a bit. 

 

The alternator is a 63amps and it was the same model number that I took off. That doesn't mean they didn't change the casing or something over time. I was looking at older pics and noticed at one point there was a double groove pulley on the alternator vs the single one that is on there now. I'm going to order one and see if the outside groove lines up better vs the one that came with the Ac-Delco alternator or find a different pulley that works. 

 

Something like this once i figured out the correct dimensions. 

 

https://www.amazon.c...tive,205&sr=1-9


Edited by aw9d, 10 February 2020 - 11:45 AM.


#6 aw9d

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Posted 13 February 2020 - 07:27 AM

Got the belts tighter and so far no squealing. I still have the whine though so I'm going to remove all the belts expect the alternator belt and see if it goes away. If not then I'd think the alternator has to be the culprit and I'll have that replaced with the AC-Delco that has the dual groove pulley. 



#7 JOE68

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Posted 13 February 2020 - 05:02 PM

power steering pumps can whine when they are low on fluid or going bad



#8 aw9d

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Posted 14 February 2020 - 09:16 AM

power steering pumps can whine when they are low on fluid or going bad

 

I actually have a feeling it is the PS pump because it's one of the only parts I haven't changed out yet under the hood.

 

Double pulley is ordered, Napa was cool enough to swap out the alternator and when it shows up we are just going to remove the pulley and swap them in the parking lot. 






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