[Bentwheelbob]

Originally Posted by njsteve

One other monkey wrench in the belt search is that you need to make sure that both the alternator belt and the power steering belt are the exact same width. If they are different widths you will get the infamous belt shriek that the idler pulley-equipped cars are renowned for. The shriek is caused by the two mismatched belts trying to compete at two slightly different speeds on the same section of the water pump and the crank pulley, at the same time. One of them ends up slipping.

I can assure you that having belts of the same width did not stop the shrieking on the Black Car. Frankly I never understood how using a belt that was bigger than the pulley groove was designed for would be helpful, but I still have a lot to learn. I am hoping using the double Teflon seal in the AC compressor and the larger WP pulley will help resolve the issue.

[njsteve]

Both belts need to ride at the same height of the V groove of the water pump and crank dual groove pulleys or they are competing against each other and not pulling at the same speed.

Kind of like when you pull the venitian blind cords on your window but the cords get out of sync and the window blind raises at a cocked angle.

Either way I have not really found a magic solution yet and would love to see an original belt set for measuring purposes. My Gramma's '75 does not seem to shreik nearly as much as the black car did. Maybe that was the reason for the redesigned idler pulley with the open face????

And now, back to our regularly scheduled thread...someone find the correct belt part number(s) please.

[Bentwheelbob]

Not so fast...

I'm not an engineer, but it seems like the shaft driven by the opposing belts would simply turn at different speeds and cancel out any tendency for the belts to be in competition.

The idler pulley on the Black Car was the open face variety.

[njsteve]

Me neither! LOL

I think the problem is the second pulley (the water pump pulley). If they were just running off the crank pulley to their respective components (alternator and ps pump) there isn't a problem. I think it has to do with the fact that the idler belt set up causes the alternator belt only "ride" in a very small section of the waterpump pulley and thus, skip off it under high loads, making the shriek.

See attached photo of The Shriek ZOne

['ol Pinion head]

Belt sizes from earlier post (3/72 dated master parts book)

Alternator:
71-72 All F /455 HO H.T.-P.S. & A.C....545297...BELT (1/2" x 49 3/4")
71-72 A, B, & G-AC, w 80amp............1378417..BELT (1/2" x 51")
(this is only belt that could be in question)

Power Steering Pump
71 A & F - P.S.-A.C......9789230...BELT...(1/2" x 52" double wrap) (w 80 amp alt)
72 F...........................9789230...BELT...(1/2" x 52" double wrap) (w 80 amp alt)
71-72 All P.S. & A.C. exc X....9790635..BELT..(1/2"x 50 1/2")(w/55amp alt)

Air Conditioning Compressor
70-72 All V/8 A.C. exc 307...478012...BELT..(1/2" x 59 1/4")
(no issues here)

hope this helps.

[Held for Ransom]

Originally Posted by Transamric

For sure what OPH said regarding using Master Parts Catalogs.
I also have been trying to pin down what my '71 A/C 80 amp TA came with. I have a near perfect build sheet with all 3 codes readable, but haven't found anyplace where the codes are translated into part numbers.
The 9/1/1971 MPC shows this:
Alt. 545297
P.S. 9789230
A/C 478012, same as OPH's 3/72 catalog.
BUT, the 1971 Firebird Product Information Manual has this on the 80 amp alt. installation pages:
Alt. 483781
P.S. 483780
A/C 478012
These pages are dated fairly early at April 1970, but should at least be correct for early '71 builds. Perhaps there were running changes in the belts used. Neither of my '71's have any original belts.

1972 Formula LS5/M40 had codes PQ (478012), P6 (483781) and NO (545297).

[Formulabruce]

Steve has it, they squeal at the small point where Both belts are on the same water pump pulley, and as he said , they compete with each other for same speed. Their depth in the pulley can and does change the relative speed by a small amount. The distance down to the idler contributes to radial vibration of the belt as well. ( rocking back and forth as it moves on its path) The fix at the dealer was replace Both belts, and make sure they did not "ride high". WE often measured and got the belts by the old fashioned way, Length, for these applications.
Thanks for re posting the number OPH

['ol Pinion head]

Originally Posted by Held for Ransom

1972 Formula LS5/M40 had codes PQ (478012), P6 (483781) and NO (545297).

But are the Alt and PS belts you mention for 80 amp use?

For a 72 TransAm, there would be 3 different pairs of alt and PD belts, depending on size of two groove pulleys.

[Held for Ransom]

Roger, I wouldn't have posted if it weren't (codes were off of a build sheet).

And, the 483780 pick code was P2.

['ol Pinion head]

Thanks Mike, thanks for posting the codes off the sheet.

The only difference I can see between '71 & '72 when identically equipped with Auto, AC, and 80 amp idler pulley is the oh so slight difference in diameter of the 481040 wp pulley, and the 38xxxx wp pulley used in '72. I sure hope Quanta has the correct width and length alt belt, just used in another GM application.

[hiyabradHO]

Originally Posted by 'ol Pinion head

Thanks Mike, thanks for posting the codes off the sheet.

The only difference I can see between '71 & '72 when identically equipped with Auto, AC, and 80 amp idler pulley is the oh so slight difference in diameter of the 481040 wp pulley, and the 38xxxx wp pulley used in '72. I sure hope Quanta has the correct width and length alt belt, just used in another GM application.

I should mention my car is a 4spd.

[Transamric]

Originally Posted by Held for Ransom

1972 Formula LS5/M40 had codes PQ (478012), P6 (483781) and NO (545297).

HFR, those match my May '71 VN TA's build sheet in Boxes #35, 36 & 37. How did you connect the pick codes with part numbers? I.E., which box number goes with which belt application?

[Held for Ransom]

Originally Posted by Transamric

HFR, those match my May '71 VN TA's build sheet in Boxes #35, 36 & 37. How did you connect the pick codes with part numbers? I.E., which box number goes with which belt application?

I'm psychic, LOL. Actually, I used the '72 Assembly Manual. Here is the sizes of the belts, noting how they stuck L in front of the others...

[njsteve]

Does this help at all? It's the build sheet from Gramma's '75 Firebird with the 80 amp setup. And it has HC, GN, GK as the belt codes in blocks 35, 36, and 37.

[Held for Ransom]

Trying not to muddy the waters, but Steve your '75 had these belts...
A/C 9433770 (HC)
Alt. 9433756 (GN) and
P/S 9433753 (GK)

[Held for Ransom]

And, my '74 belt was replaced as it should have had...
A/C 478012 (WH)
Alt. 483781 (WG) and
P/S 483780 (WC)

[hiyabradHO]

Originally Posted by Held for Ransom

I'm psychic, LOL. Actually, I used the '72 Assembly Manual. Here is the sizes of the belts, noting how they stuck L in front of the others...

My build sheet is pretty thrashed in that area but I was able to make out:

35-PQ
36-P6
37-PZ or P2

My car is a VN 12/70 build.

Can you decipher for me?

[Held for Ransom]

A/C 478012 (PQ)
Alt. 483781 (P6) and
P/S 483780 (P2).

[njsteve]

Originally Posted by Held for Ransom

Trying not to muddy the waters, but Steve your '75 had these belts...
A/C 9433770 (HC)
Alt. 9433756 (GN) and
P/S 9433753 (GK)

So according to the charts, the width/length measurements would be:

9433770 A/C: 7/16" by 59"
9433756 80 amp Alt: 7/16" by 52"
9433753 PS: 7/16" by 51-1/2"

[Held for Ransom]

The '53 is a 50-1/2 belt.