1970 LT-1 Alternator Pulley

[Bob H.]

I am trying to determine what the correct pulley is for my car. I know it should be a deep V zinc plated pulley. Answers on the internet are all over the place. I was looking at several that are either 3829387 or reproduction of it. It lists all high performance applications except the 70 LT-1. Others say a 180. Then I see many repros that don't have a key slot which I am not sure is correct. Does anyone know the correct size, etc? My alternator is the correct 884

[Joe L.]

Re: 1970 LT-1 Alternator Pulley

I am trying to determine what the correct pulley is for my car. I know it should be a deep V zinc plated pulley. Answers on the internet are all over the place. I was looking at several that are either 3829387 or reproduction of it. It lists all high performance applications except the 70 LT-1. Others say a 180. Then I see many repros that don't have a key slot which I am not sure is correct. Does anyone know the correct size, etc? My alternator is the correct 884

Bob-------


The original pulley for your application was GM #1970831 which is a Delco-Remy part number. This was a machined steel, clear zinc plated pulley of 3-3/16" OD with no keyway slot. It had no stamped part number. It was discontinued from SERVICE in November, 1984 and replaced by GM #3844100. The latter was a pre-existing Chevrolet part number originally released about 1964. It's virtually identical to the 1970831 except that its diameter was 3-7/32". I do not recall if the 3844100 had a keyway, or not. Either way, it's a moot point because a keyway is not necessary for ANY Corvette application and the presence or absence of a keyway cannot be discerned when the pulley is installed.

By the way, it's even possible that the 3844100 was used alternately with the 1970831 in PRODUCTION but I have no proof of that.

The reproductions of either of the above pulleys are very good and very close to the original configuration. The one difference is a very minor difference in the configuration and width of the belt guides. Functionally, they should work perfectly, though. Whether judges can discern the difference, I know not.

[Dennis D.]

Re: 1970 LT-1 Alternator Pulley

My 70 LT-1 884 alt. Pulled for repair.

Screenshot_20231112_180916_Gallery.jpg
Screenshot_20231112_183854_Gallery.jpg

[Joe L.]

Re: 1970 LT-1 Alternator Pulley

My 70 LT-1 884 alt. Pulled for repair.

[ATTACH=CONFIG]119428[/ATTACH]
[ATTACH=CONFIG]119429[/ATTACH]

Dennis------


Are you sure this pulley is original to the car?

[Leonard M.]

Re: 1970 LT-1 Alternator Pulley

First 2 pictures are from my CTU Jan. car. That alternator had the look of being untouched until I put my hands on it, to clean it, as seen by the adjuster bracket. Second 2 pictures are of my current CTK car that was restored, but I feel the pully is correct. Both measured 3 3/16" with no key slot or stamped numbers.
I recall Gary Bosselman did research on the pullies that were used back then.
1100884front.jpg1100884date.jpgDSCN7987.jpgDSCN7991.jpg

[Dennis D.]

Re: 1970 LT-1 Alternator Pulley

No, I'm not. Sent it out for what I thought was a bad bearing. Turns out the bore in the front cover was out of round. Have no idea how that could happen. Maybe wrong pulley?
Ken Bruno did an amazing repair.

[James G.]

Re: 1970 LT-1 Alternator Pulley

Here is the original on my LT1.
IMG_9426.jpgIMG_9462.jpg

[Joe L.]

Re: 1970 LT-1 Alternator Pulley

No, I'm not. Sent it out for what I thought was a bad bearing. Turns out the bore in the front cover was out of round. Have no idea how that could happen. Maybe wrong pulley?
Ken Bruno did an amazing repair.

Dennis------


What is the exact OD of this pulley?

[Dennis D.]

Re: 1970 LT-1 Alternator Pulley

I'll have to measure it. It's not back on the car yet. Mine looks way to thick on the rear portion.
Great , looks like I'll be searching for another part made of unobtainium

[Bob H.]

Re: 1970 LT-1 Alternator Pulley

I have ordered one that is supposed to be made exactly to the 831 specs. Thanks for the input. I'm going to compare my fan to yours as long as you believe it is original. Just trying to correct as much as possible pointed out during judging. Most are simple fixes

[Dennis D.]

Re: 1970 LT-1 Alternator Pulley

I have ordered one that is supposed to be made exactly to the 831 specs. Thanks for the input. I'm going to compare my fan to yours as long as you believe it is original. Just trying to correct as much as possible pointed out during judging. Most are simple fixes

Where are you getting the pulley Bib?

[Dennis D.]

Re: 1970 LT-1 Alternator Pulley

Joe.....
Pulley diameter=3.040.

[Joe L.]

Re: 1970 LT-1 Alternator Pulley

Joe.....
Pulley diameter=3.040.

Dennis------


It's not a GM #1970831 or GM #3844100. So, what could it be? I really do not know. Might be a GM#3883978 or GM #3906329. I think even more likely, based on configuration, is that it's some sort of aftermarket pulley.

[Dennis D.]

Re: 1970 LT-1 Alternator Pulley

Thanks Joe. Even more concerned with the thickness. Especially the thicker rear offset.

[Joe L.]

Re: 1970 LT-1 Alternator Pulley

Thanks Joe. Even more concerned with the thickness. Especially the thicker rear offset.

Dennis------


I think it should be functionally fine. As long as the pulleys reasonably align (which I'm pretty sure they do) there should be no functional problem. As far as a small difference in OD from original, that should present absolutely no functional problem, at all.