Old 06-22-2022, 02:46 PM
kingbuzzo kingbuzzo is offline
Join Date: Mar 2022
Posts: 73
Default 74 T/A FB Alternator options and rear bracket?

Hi Fellas:

I'm looking to dump the chrome dome alternator that came with my newly acquired T/A however it only has a bracket on the front.

Was there a rear bracket for the stock unit and if so what does it look like?
Seems to me it will move under load without a rear bracket.

I went to the parts store and they had a massive 80a alternator listed for my car however it doesn't fit the bracket I have.

What options do I have other than the smaller stock 40a that they do stock and appears to fit the stock bracket?


Old 06-22-2022, 03:09 PM
68bird400HO's Avatar
68bird400HO 68bird400HO is offline
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Join Date: Aug 2004
Location: Surrounded By Reality
Posts: 2,003

Does the car have AC and/or rear defrost? If it has one of those but not the other then just go with a stock 55a unit. If it has both, then your car should have come with the 80a setup.

1968 Firebird 400HO convertible
1971 Trans Am 4-speed, white/blue
Old 06-22-2022, 03:43 PM
unruhjonny's Avatar
unruhjonny unruhjonny is offline
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Join Date: May 2004
Location: Calgary, AB, Canada
Posts: 5,632

if my memory serves me you should absolutely have two brackets.
I believe the set up was essentially the same from 73-75(??)...
IIRC the rear bracket used a studded front thermostat housing bolt as a mounting point - and one or two studded intake manifold bolts on the drivers side head.

Here's a couple image links I just found for you:

1974 SD455 image

1975 Trans Am

1970 Formula 400
Carousel Red paint on Black standard interior
A no-engine, no-transmission, no-wheel option car.
Quite likely one of few '70 Muncie three speed Formula 400's left.

1991 Grand Am: 14.4 @ 93.7mph (DA corrected) (retired DD, stock appearing)
2009 Cobalt SS: 13.9 @ 103mph (current DD; makes something north of 300hp & 350ft/lbs)
1 Corinthians 2:12-14 / Ephesians 2: 8-9 / Luke 23: 39-43 / 2 Timothy 3:1-5;12
Old 06-22-2022, 04:21 PM
kingbuzzo kingbuzzo is offline
Join Date: Mar 2022
Posts: 73

She has air but no defrost. Are you saying if it was equipped with A/C & defrost it would have a different physical size unit and associated bracketry?


Old 06-22-2022, 04:23 PM
kingbuzzo kingbuzzo is offline
Join Date: Mar 2022
Posts: 73

Oh I can see it now - thanks!

Pretty sure that is what I need.

Do you have one in stock and/or want to trade for my extra front bracket lol...

Would a 50a stock-ish type unit suffice if I'm adding a loud annoying radio? My old t/a would suck the battery dry when I was at the lights with headlights and radio blaring - trying to avoid that scenario.

Old 06-22-2022, 04:57 PM
455dan's Avatar
455dan 455dan is offline
Join Date: Oct 2020
Location: North
Posts: 78

I replaced my 63 amp with this 10si unit for $100

claimed 110 amp output and can be wired 1 wire self excite or factory 3 wire.

No problems with it other than I did have to re clock the back piece and when I did the brushes popped loose so ended up checking it out and re assembling. No rear bracket on this one and it does not move. but a rear bracket can't hurt.

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1984 RX7 Jim Hand style 455 /200 4R Project car
67 White/Gold GTO 4 speed sold, 1968 GTO 4 speed sold, 1969 GTO auto sold, 68 Firebird 400 4 speed (455) sold, 65 GTO Night Watch Blue 4 speed sold, 64 GTO Nocturne Blue 4 speed sold, 71 GTO Gold auto sold. 1975 Formula 400 auto sold.
Hopefully to be restored, H-"O" Racing 73 Trans Am SD 4 speed,
Sons 70 Formula 400 auto, and wife's 1974 AMX 360 auto, 1975 Jeep Honcho 4x4, 1965 Buick Special post

Last edited by 455dan; 06-22-2022 at 05:12 PM.
Old 06-22-2022, 06:24 PM
Formulabruce's Avatar
Formulabruce Formulabruce is offline
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Location: North East of AMES PERFORMANCE, in the "SHIRE"
Posts: 8,803

80 amp option was a FIXED position unit and Only came
With 2 configurations. AC + GRID rear defrost, OR AC and Power Windows. This has an Idler pulley set up. Way lots more than needed with today's tech.
Rear bracket. The 80 amp rear bracket IS DIFFERENT.
I have seen a few base birds ( 350 v8) from 70- 77 that when New, did Not have a rear bracket on the 37 amp alternators.
The Front Alternator bracket changed in 75 and the adjuster screw goes in from the front side of the alternator. This probably did move the support out further, but its close to in line with the pulley where the stress is.
You can easily run a rebuilt or new 10si, or 12si , 100 amp unit on these cars and rear bracket is common to 71 to 77, regardless of the front bracket being different.

"The Future Belongs to those who are STILL Willing to get their Hands Dirty" .. my Grandfather

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