'67 L79 Alternator and Pulley

[Mark S.]

I have a '67 L79 with power steering and no AC. My car has an incorrect alternator which is 1100774 - 55A, dated 6K4 which I am told is from a '66 Buick. I believe the correct alternator for my car is 1100693 (37A) with pulley 3875968AW according to the JG. Can anyone describe what this pulley looks like or provide the diameter? Also, where can I get one?
Thanks in Advance,
Mark

[Joe L.]

Re: '67 L79 Alternator and Pulley

Mark-----

Despite what the JG and, even, the AIM might indicate, your application did not use a GM #3875968 pulley assembly. It would have used this pulley assembly IF it had been equipped with a 62 amp alternator. However, NO 1967 Corvettes were ever originally built with a 62 amp alternator, although other 1967 model year Chevrolets were so-equipped.

The GM #3875968 was a pulley assembly which consisted of a stamped steel pulley of 2-21/32" OD, one 3/8" groove, and an integral fan. It was replaced for SERVICE in April, 1967 by the GM #3909817. This is a very similar assembly, the difference, if I recall correctly, being a slight change in the fan configuration. The pulley section is identical. It was discontinued many years ago and is not reproduced. They do show up for sale on eBay from time-to-time.

The pulley used for your application was of GM #3829387. This is a machined steel pulley of 3-5/8" OD and 1/2" groove. It has no integral fan and, instead, uses a separate fan.

[Mark S.]

Thank You Joe

Thank You Joe. That is exactly the kind of information that I was looking for.
Mark

[Joe L.]

Re: Thank You Joe

By the way, the GM #3829387 was available from GM until quite recently. It's also easily available in reproduction. There might still be some of the GM pieces around. Originals were zinc plated and usually had no irridite (gold) overplate. Later GM may have the irridite overplate. IF DESIRED, this is easily removed by dipping in a VERY weak acid solution for just a few seconds. Then, you have a zinc plated pulley with no irridite overplate. Would I do this? No.

[Joe L.]

Addendum

One other thing so that no one gets the wrong idea, while I don't think that the GM #3875968 and GM #3909817 pulley assemblies were ever used on any L79 application, they were definitely used for SOME base engine applications. The 3875968 was likely used for very early builds of such applications and the 3909817 for later builds.

[Paul L.]

Re: '67 L79 Alternator and Pulley

I have a 1100693 7A25 37A alternator but I cannot find a number on the pulley. Is it on the backside? I measure the diameter at 2 9/16" but my tired eyes may have shrunk it from Joe's 2 21/32." Does the pic indicate a "correct" pulley for a base 327? It was painted black at some point.

[Mark S.]

Re: '67 L79 Alternator and Pulley

Paul,
When was your car assembled? Mine was assembled April 4, 1967. I need to check this but I believe that means an 1100693 alternator built in Jan-Mar 1967 would be correct for mine.

I looked on the pulley of my "Buick" alternator that measures 3" OD x 3/8 groove width and I could not find a part number.

[Paul L.]

Re: '67 L79 Alternator and Pulley

Mark,
I believe that 7A25 is January 25, 1967. The build date for my car is February 10, 1967 so that alternator should be in the appropriate date range for my car.

[Paul L.]

Better Pic of Numbers *NM*

[Mark S.]

Thank You Paul

Thank You Paul...it sounds like a more appropriate date for my alternator, given its April 4, 1967 build date, would be March 1967 or 7CXX.
Mark

[Rick S.]

Re: Thank You Paul

My car is a June 19th car and it has the 1100693 37 amp alternator with a date stamp of 7C28.

[Joe L.]

Re: '67 L79 Alternator and Pulley

Paul-----

This is not the pulley I would expect for your 300 hp application. The pulley that I would expect would be either a GM #3843342, GM #3909815, GM #3875968, or GM #3909817, depending upon when built and other installed options. All of these pullies have integral fans. Functionally, what you have may be equivalent to 1 or more of the above and, I suppose, it's possible they were alternately used. Not to my knowledge, though.

The pulley that you have may be a GM #3871241, GM #3871253, GM #3792460, GM #1949355, GM #1949356, GM #1949357, or one of several other pullies. As far as OD goes, are you measuring the maximum OD (rear on these pullies) or the OD on the front? In any event, GM specs are often based on some sort of "measuring protocol" that I've never fully understood. So, it's not uncommon to find a pulley of known part number differing from the GM published spec.

Check the front (smaller OD) surface of the pulley. There MAY be a single stamped number found there. If it's there it's usually lightly stamped and may be hard to see. Often times, though, there are NO identifying numbers on these pullies. Given the PLETHORA of alternator pullies, many with very slight differences, this was a VERY DUMB thing for GM to do.

[Paul L.]

Re: '67 L79 Alternator and Pulley

Joe,
I measured the outer surface initially. The inner surface is indeed larger. I eye-ball it at 2 5/8" but it is probably 2 21/32" as you mentioned.

I can't see a number. And although the alternator seems correct, I have no idea if the pulley is. I must admit my ignorance at that level of detail. My pics were just for Mark's reference. Nevertheless I very much appreciate your comments.