[dld]

My 70 car has this alt. from reading the threads on 70 alt. this seems to be wrong.

the a
Ames book showes this style for my car .

it does have the correct plug

straighten me out on this ... Please

not necessary to be correct , car has A/C and windows

[racerboy]

I’m no expert, but I don’t think either of the alternators pictured in the Ames book are ‘correct’ for a ‘70. I’m not sure about a car with A/C and power windows, but the standard 37A alternator has an open-face front, a 6-spoke casing, and a diamond-shaped cooling fin in the back. I think the 6-spoke casing and the cooling fin are unique to 1970, but could be wrong.

RamAirNacho has a whole thread on theses which is where I learned most of what I know.

Here’s an example of a beautiful 37A unit restored by a fellow PY member:





Sent from my iPhone using Tapatalk

[Ramairnacho]

That looks like the 11100700 external alternator with a Chevy fan. But I'm still learning

[Ramairnacho]

Originally Posted by racerboy

I’m no expert, but I don’t think either of the alternators pictured in the Ames book are ‘correct’ for a ‘70. I’m not sure about a car with A/C and power windows, but the standard 37A alternator has an open-face front, a 6-spoke casing, and a diamond-shaped cooling fin in the back. I think the 6-spoke casing and the cooling fin are unique to 1970, but could be wrong.

RamAirNacho has a whole thread on theses which is where I learned most of what I know.

Here’s an example of a beautiful 37A unit restored by a fellow PY member:





Sent from my iPhone using Tapatalk

Did you find one yet text me when you can

[Ramairnacho]

I believe these pics will help the 60s cars had different alternator. This Is gto early alternator I think. Im.still learning no an expert or professional Yaker. This is a hobby for me. View pics of alternator. It's dated 8m13. I think that's Dec.13,1968. And is a 11100700 for gto with ac. I have a few alternators but if you want an original they aren't cheap.

[Ramairnacho]

It might be internal regulator im.not an expert. Does it work is the question?

[Formulabruce]

Originally Posted by dld

My 70 car has this alt. from reading the threads on 70 alt. this seems to be wrong.

the a
Ames book showes this style for my car .

it does have the correct plug

straighten me out on this ... Please

not necessary to be correct , car has A/C and windows

This alternator is a 12si unit.It is an Excellent unit used throught the 80-90's. They are considered a cooler running upgrade to a factory 10si which was first used in later '69 Firebirds and 1970 Firebirds.
Also looks like the 37 amp unit of the 1970 Firebirds was used in 6 cyl Firebirds as well. This could be why I have seen some that are 10DN, and not 10Si. ( SI means "Systems Integrated" ) This is internal regulation.

[Formulabruce]

As discussed in other threads and verified by OPH, myself and many others the Fan ( which is correct on this) should be bright Galvanzined when new ( 5 months and it was not so shiney)
The Pulley should be Gold Anodized in appearance.

[Formulabruce]

Yes, I have seen Wrong colored ones at MACN.. gasp.... Its an easy fix though...

[dld]

Great info. as always . Thank you all!

This was on car when I bought the car . no history on the Alternator. probably a reman. there are no numbers on case .

I took it apart to detail it and now it does not work . I was careful but! I did replace the bearings, and it is a internal regulator alt.

Now, I have to find parts to rebuild it or find a unit that will be more correct . car is modified to where nothing is so original but would like to keep it at least appearing correct.

[Ramairnacho]

Originally Posted by Formulabruce

This alternator is a 12si unit.It is an Excellent unit used throught the 80-90's. They are considered a cooler running upgrade to a factory 10si which was first used in later '69 Firebirds and 1970 Firebirds.
Also looks like the 37 amp unit of the 1970 Firebirds was used in 6 cyl Firebirds as well. This could be why I have seen some that are 10DN, and not 10Si. ( SI means "Systems Integrated" ) This is internal regulation.

Formula Bruce
What is the advantage of the 12si unit. I.disnt know that was a newer style alternator. I seen on ebay that style advertised as mid 60's gto alternator on ebay. So I assumed they where mid 60's. So the stamps on these units are incorrect?

[Formulabruce]

The 12si alternator was built to allow higher amps, without a big case alternator, like the 80 amp unit used in the 70's which was/ is a fixed position alternator that requires a idler assembly. This alternator, like the 10si discussed here, uses " Back to front" cooling. This cools the regulator heat sync first. The front fan used a partial plastic redesign of the fan for more efficiency. While you would not expect it, Alternators cool best from airflow which come in the back, and exits where the engine cooling fan is blowing back against it. The 12si was Never used on any 60' s or 70's GM cars and as I recall was a later 80's design.

[Formulabruce]

Originally Posted by dld

Great info. as always . Thank you all!

This was on car when I bought the car . no history on the Alternator. probably a reman. there are no numbers on case .

I took it apart to detail it and now it does not work . I was careful but! I did replace the bearings, and it is a internal regulator alt.

Now, I have to find parts to rebuild it or find a unit that will be more correct . car is modified to where nothing is so original but would like to keep it at least appearing correct.

You have a couple options for " Looking the part"
1. Look on ebay for a 71 corvette alternator. They used an open face. I have bought a few that were low amp and used on big block cars with no AC. IF IT IS A "DN" ( external regulated) alternator Thats fine, you only need the front, and you can clean it and install on your 12Si rear case once you fix it.
>>>> TOP TIP》》 the open face Alternators used a DIFFERENT front bearing holder on the inside than a more common full support front case. 《《《.
So.. if you guys buy a front case, get it with the bearing and most importantly the bearing holder.
2. Buy a reman blank or not correct, but correct looking alternator. I have built a few open face that work fine and look the part sitting right there in front of the 400 so it looks right. I know guys who use these and boxed the original.
Pic below is just a moc-up for checking brackets and pulleys on a 1970. Alternator is not restored yet, so colors are not right. Its a Corvette 37 amp case that will be rebuilt to 110 amp. It will look the part, and work, but not 100% correct and fan is incorrect for the 1970 firebird.

[Formulabruce]

Lastly, once you bead blasted a case ( NOT SAND, BEADS) wear clean gloves to keep your skin oil off the bare casting.
Once rebuilt, with gloves, use RPM on the case at over 65 degrees. Can even use a second coat. This will keep your alternator looking really nice for years. RPM is " Rust Prevention Magic " it is sold by ECS automotive, and its a little paste. It is on 99% of cars at MACN. there are videos on their site here scroll down once you click link. https://ecs-automotive-concepts.mysh...f76a492c&_ss=r

[dld]

Big help . I have a better understanding on what's happing now .

I have that RPM presentive . I use something similar on my 65GTO bare parts I get from RESTO-GAURD . the drive shaft in the 65 is bare steel and it stays nice

['ol Pinion head]

Originally Posted by Ramairnacho

That looks like the 11100700 external alternator with a Chevy fan. But I'm still learning

1100700's & 1100700's are 10 DN's, external regulated alts, last usage of a 10 DN was on a '70 Pontiac (exc 70 V8 Birds). Olds Cutlasses & low horse 442's kept running 10DNs at least through '72 model.

Though smooth in appearance, the above 12SI alt is slightly larger case/internal regulated alternator. These were introduced on Pontiacs in '79. When I specially ordered my '80 SE Turbo, I ordered it with the grid type defroster & halogen lights. Within a week my Dad @ work received a memo back from Pontiac Zone 20, as I was required to order the HD alt with those additional options. This was the 70 amp 12 SI alt. PS & alt brackets are also different for this style alternator.

[Ramairnacho]

Thanks then I'm reading alternator incorrectly? It looks like the 12si but has 1100700 stamped on it.

[Kenth]

There is no 1100700 12Si alternator.
The 1100700 is a 10DN alternator.

So how can a 1100700 alternator look like a 12Si alternator?

[Ramairnacho]

Oh the back plate isn't a complete circle. I'm learning all this stuff from other members.

[Formulabruce]

Originally Posted by Ramairnacho

Thanks then I'm reading alternator incorrectly? It looks like the 12si but has 1100700 stamped on it.

This doesn't look like a 12 Si at all. Big tell tale for starters is the plastic fan set up.