[njsteve]

I found a cure for the always-squeeling alternator belt on the 80-amp alternator setup. While this may not suit the guys who want an absolute original setup for concours judging, it does solve the problem completely.

I removed that dreaded idler pulley and found a belt that is the exact length to fit without having the idler pulley. A 15485 belt works perfectly. (keep in mind the factory length belt for the 80-amp with A/C is 15515 and without A/C is 15495)

Here are the specs on the 15485 belt I used:

Outside Circumference (in) 49.125
Outside Circumference (mm) 1247
Top Width (in) .375
Top Width (mm) 10

I removed the idler pulley off its bracket and then unbolted the alternator and fit the new 15485 belt over the alternator pulley. I then reinstalled the alternator. That was it.

The 15485 belt has just the right amount of tension - not too tight or too loose. There is no longer any way to adjust it but it seems to work perfectly, riding along the water pump pulley for a far larger contact area than the one inch or so that it would touch the groove with the idler pulley in place. That is the reason for the squeel with the factory setup - at higher RPMs the alternator belt bounced off the top of the pulley instead of riding tightly in the groove.

I have performed repeated test procedures employing my patented/copyrighted SFDTP. (Shaker Flapper Door Testing Protocol: at 50 mph, slamming the pedal to the floor with a resulting high speed third to second gear downshift). No noises other than the angry 455 sound from the open shaker door and the gas gauge moving rapidly to the left.

Here's the after photos and a couple shots of the untouched setup on my 73 SD:

[Pepi]

Nice research Steve, but I thought I read on another thread where someone said they started going through water pumps when they omitted the idler pulley. They may not have done enough research as you did and had a belt that was too tight.

[njsteve]

I went through rockauto and ordered half a dozen belts in varying lengths, so I had a full selection ranging from 15460 to 15585. When added to my assorted old belts around the garage I had a belt for every half-inch increment you could think of. I spent a couple days finagling with them til I found one that worked.

Also keep in mind the belt width too, The narrowest version (3/8 = .375) of the 15485 is what worked. I had several that were wider than 3/8 and it was too tight. The widths I tested ranged from .375 (perfect) to .410, .440, .469 and even wider. That's quite a big jump: 3/8, 13/32, 7/16, and 15/32.

Since rockauto had the old belts on sale, most were only a couple bucks apiece and all came from the same location so I lucked out on the shipping too.

[RicksGTO]

I just did the same with rockauto and they had a lot of the .47" width belts on sale as well so I bought a couple of lengths for each belt. I found the .47" width on both the power steering and alternator belt stopped mine from squealing and they ride up higher in the pulleys which I believe is better for preventing slipping. The Gates numbers for the belts I found worked were A48 for the power steering and A51 for the alternator/idler pulley. I also used the Gates replacement idler pulley we found back when you were doing the white T/A as an alternative to the captured bearing unit from the factory so that may be part of the improvement as well.

[johnta1]

I removed that dreaded idler pulley

This was a bulletin in 1972:
(believe I posted before somewhere)

Adjustable pulley replacement

Part 2

Supposed to be for A-body, not sure why it wouldn't work for the Firebird?

[njsteve]

Do you have the full bulletin?

[DavesGTO]

If the same setup as the GTO, I replaced the bearing in the idler pulley. Same bearing used in the alternator is used in the pulley.


Sent from my iPhone using Tapatalk

[Pepi]

Originally Posted by johnta1

This was a bulletin in 1972:
(believe I posted before somewhere)

Adjustable pulley replacement

Part 2

Supposed to be for A-body, not sure why it wouldn't work for the Firebird?

That is an interesting bulletin. I too would be interested in seeing the whole bulletin.

[johnta1]

That is the full bulletin, actually called a Service Letter I guess?
(the 2nd link I posted is page 2)

71-ST-9 is the number for it. Dated 10/15/1971

[njsteve]

Amazing bulletin. I'd love to get one of those 9790677 brackets. I had no idea they actually had a fix already, for this problem.

Interesting that they don't show the need for a different belt in the bulletin.

They actually list that as a fix for later models too, in the parts book:

9790677 1971/8 CYL WITH 80 AMP DELCOTRON — EXC
IDLER PULLEY, 1972-75/8 CYL PONT ENG W/80 AMP
DELCOTRON

In theory, if you just welded on another inch of metal onto the existing mounting tab and slotted the hole, you'd have an adjustable bracket to match the 9790677. Since the rear bracket is already fully slotted to allow for this revised adjsutment arc. See photos.

['ol Pinion head]

Originally Posted by njsteve

Amazing bulletin. I'd love to get one of those 9790677 brackets. I had no idea they actually had a fix already, for this problem.

Interesting that they don't show the need for a different belt in the bulletin.

They actually list that as a fix for later models too, in the parts book:

9790677 1971/8 CYL WITH 80 AMP DELCOTRON — EXC
IDLER PULLEY, 1972-75/8 CYL PONT ENG W/80 AMP
DELCOTRON

In theory, if you just welded on another inch of metal onto the existing mounting tab and slotted the hole, you'd have an adjustable bracket to match the 9790677. Since the rear bracket is already fully slotted to allow for this revised adjsutment arc. See photos.

Steve, The problem with the later style alt bracket is it swivels the 80 amp alt up too high and rubs up against the hood, thats with the stock length A-B series belt. Now if you were to section the adj slot & weld it back on, maybe it would work, I haven't gone to the effort to try several different length belts. If you need an adj style front bracket, have a few.

['ol Pinion head]

Steve, do you remember who was going through the early style idler pulleys? I'll go back in your '72 T/A restoration thread if needed.

[njsteve]

Wasn't it Pepi who was rebuilding the sealed ones?

Do you have the actual 80 amp bracket mentioned in the bulletin or one of the fixed position ones like on my car, that I could modify?

[Pepi]

Yes, I rebuild the early style pulleys. I have done a few for other members here and just sent one off to another member Saturday.
If anyone is looking for getting any done,just give me a shout.

['ol Pinion head]

Originally Posted by njsteve

Wasn't it Pepi who was rebuilding the sealed ones?

Do you have the actual 80 amp bracket mentioned in the bulletin or one of the fixed position ones like on my car, that I could modify?

Yes, Steve, have a few 80 amp front brackets with the adj slot, dropping you a PM.

Pepi, dropping you a PM too, guess I'm hard headed & would like my '72 to use its idler pulley.

[njsteve]

I replied back. I'll take it. This way I can take some side by side comparison photos and post them here.
Now I can take the rest of the idler pulley mounting hardware off...and finally see my timing marks!

[Pepi]

'ol Pinion head,
I replied back to your PM.

Thanks,
Karl

[Mark66]

So I'm reading the "Service Idler Pulley" Service Letter and I notice that it had been mailed by Pontiac to a Mr. Robert Cantoreggi. Hmmm., an unusual name that name rings a very faint bell......

So I dig through my pile of Pontiac paper and find a "Pontiac Service Information 1966" big (2 inches thick) red binder that seems to be an "official" complete compilation of Pontiac written communications sent to all (?) Pontiac dealers in 1966. It includes New Flash bulletins, Service Management bulletins, Service Confidential bulletins, special reports, Pontiac Craftsman Service News, P&A Extra letters, W&P Confidential letters - even the rarely seen "Pontiac Motor Division Listing of Product Bulletins - Passenger Car Recall Campaigns 1960 through 1966 Passenger Car Models to Date. And almost all of them sent to Mr. Robert Cantoreggi in Westfield, Mass.

Now, I do not know who Robert Cantoreggi was (a Pontiac Service Manager?) but I salute his organized pack-rat mentality as it has allowed this binder to survive to this day - how I do not know and have long since forgotten how i got the binder. But just think of the number of times it could have been thrown out, sent to a land fill, burned, lost, etc. And then to find that the "Service Idler Pulley" Service Letter was also sent to him......... well, I am going to have a beer or two in his name tonight. Wish there were more like him in this world. Maybe we would then have has a copy of a 1966 Big Pontiac assembly manual. Robert - this Bud's for you!!!

[johnta1]

That's cool!

The way I understand it, he was probably the service manager at the Pontiac dealership.
(they were for the year I believe, each year got a new binder)

Pontiac sent these to every dealer for them to insert into that binder.
Plus some dealerships received more than one copy. Not sure who all got them. I think some mechanics got a copy?


Mine usually came from a dealer that went out of business, they auctioned off all the stuff or sold it to someone else.

When our dealer went out of business, i bought almost all the service manuals, didn't see any of the binders though.
They may have sold them to the new owners?

Anyway, most of my bulletin manuals are from different dealers, so they probably have different names.

[njsteve]

Ol Pinion Head was nice enough to send me one of the adjustable brackets. I have attached some comparison photos of the two brackets on top of each other. All the holes line up exactly and it appears that the lowest adjustment location is the exact same as the single bolt hole for the bracket from the idler pulley equipped setup.

I also see why they only used it on the A-bodies. The very tip of the bracket touches the underside hood bracing in front of the shaker opening in the hood on an F-body. I put some blue tape on the tip of the bracket and dabbed it with some teflon sealer. I then closed and latched the hood. It closed completely but it left a small dab of the teflon sealer on the underside of the hood where it touches.

So tomorrow, I am going to cut an inch or so off the top of the bracket and weld it back together. I have no idea why they made the bracket with four inches of adjustment when it only needs to be at the very bottom position with a 15495 or 15490 length belt. It could have been usable across all vehicle platforms if they had made it just a tiny bit shorter.