Pulleys for 1966 L79 with power steering

[Joe L.]

Re: Pulleys for 1966 L79 with power steering

Joe was 3875968 used on 327/300hp cars?

Brian-----


No, 300 hp used a standard groove pulley set.

[Brian K.]

Re: Pulleys for 1966 L79 with power steering

Joe, Mark and Jim's research show the 3875968 used on 300hp cars with either AC or AIR or combo any of these with PS (a pretty rare bird like you say). If we knew for sure 3875968 was a deep groove pulley I would think this would answer the question. I doubt a L79 would lack a deep groove in this location and doubt a 300hp regardless of options would have a deep groove pulley. Someone need to find a 3875968!

[Joe R.]

Re: Pulleys for 1966 L79 with power steering

Brian-------


As far as I can determine, the GM #3875968 is a deep groove pulley. However, it's kind of unusual in that it's a stamped steel pulley with integral fan.

By the way, while the GM #3829387, original or reproduction, is very easy to find, the GM #3875968 is extremely difficult to find. The 3875968 is not to be confused with its standard groove "sibling", GM #3843342. The latter is quite easy to find.

I want to correct an earlier mis-statement that I made, and then offer a few more tidbits that hopefully are not mis-statements.

Earlier I said that when the L79 was equipped with *both* PS and A/C, the alternator pulley was standard-groove. According to a table I assembled a few years ago for 1967 Corvettes, it turns out that for this particular L79 configuration, all the other pulleys were standard-groove (same parts as the 300 HP engine), but the alternator pulley was a deep-groove, 3.0" in diameter, #3846180.

For 1966-67, I believe that for the L79 with just PS, the alternator pulley was a deep-groove, 3.6" diameter pulley, #3871242 or #3829387 (both are deep-groove 3.6" diameter, but I believe they have different offsets).

The base L79 appears to have used the 3.6" #3871242. I can't think of any reason that GM would have needed to change the alternator pulley offset when they added just PS to the L79, but for some reason that is what my table shows, and it is what Mark Gorney's tables showed at the time.

What GM *did* change was the diameter of the alternator pulley whenever the engine was used with A/C. They made the alternator pulley diameter smaller, so that the alternator would spin faster to help keep up with the A/C electrical load. My table says that for 1966-67, the L79 with A/C used the deep-groove, 3.0" diameter #3846180.

Regarding the mysterious #3875968, here is something interesting. In the version of Mark Gorney's table that I have on file for 1966, the #3875968 alternator pulley is assigned to just the 300 HP base engine with A/C. This implies that it was smaller in diameter than the 300 HP non-A/C pulley. Then, in my copy of Mark's 1967 table, he shows #3909817 as the alternator pulley used for the 300 HP engine with A/C. Next to that entry Mark has a note that prior to 4/67, this part was #3875968.

So, at the time Mark made the table versions I have on file, it would appear that the 3875968 was a standard-groove pulley used only on the 300 HP engine with A/C. I do not have any info about the diameter of the #3875968, but my notes show the replacement #3909817 as being 2.7" in diameter.

For the OP who has a 1966 L79 with just PS, it appears to me that his alternator pulley should be a deep-groove pulley that is 3.6" in diameter. As noted above, I suspect that the correct part number is either #3871242 or #3829387.

[Steven L.]

Re: Pulleys for 1966 L79 with power steering

Thanks for your help, Joe. That makes sense to me, but it's amazing how little info there is clarifying it in the printed sources that I've seen. Also, regarding my situation with the '66 L79 with p/s, does the p/s belt go around the crank and water pump pulleys, or does it just go around the crank pulley?

[Leif A.]

Re: Pulleys for 1966 L79 with power steering

Read this thread from January of 2016. Pay special attention to post #9 from Joe Lucia.

https://www.forums.ncrs.org/showthre...pulley-C60-N40

[Joe L.]

Re: Pulleys for 1966 L79 with power steering

Thanks for your help, Joe. That makes sense to me, but it's amazing how little info there is clarifying it in the printed sources that I've seen. Also, regarding my situation with the '66 L79 with p/s, does the p/s belt go around the crank and water pump pulleys, or does it just go around the crank pulley?

Steven------


The power steering pump pulley for your application encircles the crank, waterpump, and power steering pump pulleys. Your power steering pump pulley should be a cast iron pulley. If you have a stamped steel p/s pump pulley, that's incorrect.