Rare Pulleys

[Joe L.]

For those that may never have seen them, I'm attaching photos of 2 rare pulleys [none for sale]. These pulleys were used for 1965 L-79 with C-60 and N-40. These are the power steering pump pulley, GM #3868892, and the power steering pump driver pulley, GM #3827843, which was "sandwiched" on the front of the GM #3850838 balancer pulley. In the first photo of the GM #3868892, I show it next to a GM #3770509 power steering pump pulley which is one of the three common Corvette small block power steering pump pulleys. While the 3770509 is very common, the 3868892 is decidedly uncommon.

[Keith B.]

Re: Rare Pulleys

Since when could you get PS in 65 with a solid lifter SB with a five quart pan

[Joe L.]

Re: Rare Pulleys

Since when could you get PS in 65 with a solid lifter SB with a five quart pan

Keith------


I "mis-spoke". I should have said "L-79". I corrected it.

[Richard M.]

Re: Rare Pulleys

Joe, Thanks for that info on the pulleys. I've never seen photos of those.

And BTW, one or two typos in nearly thirty seven thousand helpful and informative posts is unacceptable. You need to do better than that!

Rich

[Gary B.]

Re: Rare Pulleys

Joe,

Just curious. Do any of the NOS pulleys you own have the GM-speced "Parkolac 30" material as a surface treatment?

Gary

[Joe L.]

Re: Rare Pulleys

Joe,

Just curious. Do any of the NOS pulleys you own have the GM-speced "Parkolac 30" material as a surface treatment?

Gary

Gary-----


Yes, as I recall, at least a few of them do.

[Joe R.]

Re: Rare Pulleys

For those that may never have seen them, I'm attaching photos of 2 rare pulleys [none for sale]. These pulleys were used for 1965 L-79 with C-60 and N-40. These are the power steering pump pulley, GM #3868892, and the power steering pump driver pulley, GM #3827843, which was "sandwiched" on the front of the GM #3850838 balancer pulley. In the first photo of the GM #3868892, I show it next to a GM #3770509 power steering pump pulley which is one of the three common Corvette small block power steering pump pulleys. While the 3770509 is very common, the 3868892 is decidedly uncommon.

Hi Joe L:

Thanks for posting photos of these very rare pulleys. For several years I have been trying to find samples of these to examine. I'm hoping that you can answer some follow-up questions I have about these pulleys and the dual-groove crank pulley that was used with them.

A few years ago I did a little "research project" to try and figure out why the 1967 L79 with A/C and PS used the standard-groove pulley set from the base engine with A/C and PS (same water pump and crank pulleys), rather than the deep-groove pulley set from all other L79 configurations with A/C.

My conclusion was that with both A/C and PS, the triple-groove stack-up on the crankshaft would be too tall to properly align with a deep-groove pulley on the PS pump. Since the high performance deep-groove pulleys are 1/8" thicker than the standard-groove pulleys, using a triple stack-up of deep-groove pulleys on the crank would push the PS pump pulley 3/8" farther forward than the base engine configuration. This creates a very tight clearance problem between the PS pump pulley and the frame that might not work for normal production tolerances.

During this research project I heard that certain 1965 high performance small blocks with A/C and PS used a deep-groove pulley set in combination with the two rare pulleys that you show in your post. I've always wanted to see samples of these to figure out how they were configured to deal with the clearance problem, and why GM did not continue to use these same pulleys in 1966-67.

Based on the photo you show of a 3868892 PS pump pulley next to the more common standard-groove 3770509 PS pump pulley, it is clear that the 3868892 places the grove somewhat more forward than the 3770509. This suggests that the corresponding 3827843 crank pulley was stacked on top of a dual deep groove pulley such as the 3858533 used on other L79 configurations. The 3850838 dual-groove crank pulley that you mention in your post is a standard-groove pulley that was used on the base engine with A/C and PS.

Also based on the same photo in your post, the 3868892 appears to be a standard-groove PS pump pulley like the standard-groove 3770509 pump pulley next to it.

As I see it, there are three possible crankshaft pulley stack-ups that GM could have used on the 1965 L79 with A/C and PS:

1) A dual standard-groove crankshaft pulley combined with a standard-groove PS add-on pulley
2) A dual deep-groove crankshaft pulley combined with a standard-groove PS add-on pulley
3) A dual deep-groove crankshaft pulley combined with a deep-groove PS add-on pulley

Based on what I see in your photos, I think that that GM used option #2. If so, the corresponding dual crankshaft pulley would not have been the 3850838, which is a standard-groove pulley. My guess is that you would find that the 3827843 add-on crank pulley nestles snugly inside a dual deep-groove pulley such as the 3858533, while it would stick out about 1/4" from the standard-groove 3850838. I see no reason that GM would do this, but it's not impossible that they did. It's just that there would be no apparent benefit to using this instead of the PS pulleys from the base engine with A/C and PS.

So, after all the above explanation, here are my questions:

1) Can you check your files to see whether the pair of pulleys you show in your post might have been used in combination with a dual deep-groove crank pulley such as the 3858533?

2) If you have ready access to a 3858533 pulley, can you check to see if the 3827843 add-on crank pulley nestles snugly inside the 3858533 pulley?

3) Lastly, can you compare the groove width of the deep-groove 3858533 to the groove widths of the two pulleys in your posting?


My current theory is that to provide a bit more frame clearance for the PS pump pulley on the 1965 L79, GM combined standard-groove PS pulleys with a deep-groove dual crank pulley. This would preserve the high performance deep-groove pulleys for the water pump and the dual crank pulley, and would only push the PS pump pulley 1/4" forward compared to the base engine pulley set for A/C and PS. Using a full deep-groove pulley set on the L79 would push the PS pump pulley 3/8" forward compared to the base engine pulley set.

If GM did this for 1965, it is possible that they found that normal production tolerances still created occasional problems with frame clearance for the PS pump pulley. If so, this might be the reason that they switched to using the base engine pulley set for 1966-67 L79s that had both A/C and PS.

I'm hoping that you can help solve this mystery about the 1965 configuration, since it appears that I will never get my hands on samples of the very rare 3868892 and 3827843 pulleys to study in person.


Thanks,

Joe Randolph

[Joe L.]

Re: Rare Pulleys

Hi Joe L:

Thanks for posting photos of these very rare pulleys. For several years I have been trying to find samples of these to examine. I'm hoping that you can answer some follow-up questions I have about these pulleys and the dual-groove crank pulley that was used with them.

A few years ago I did a little "research project" to try and figure out why the 1967 L79 with A/C and PS used the standard-groove pulley set from the base engine with A/C and PS (same water pump and crank pulleys), rather than the deep-groove pulley set from all other L79 configurations with A/C.

My conclusion was that with both A/C and PS, the triple-groove stack-up on the crankshaft would be too tall to properly align with a deep-groove pulley on the PS pump. Since the high performance deep-groove pulleys are 1/8" thicker than the standard-groove pulleys, using a triple stack-up of deep-groove pulleys on the crank would push the PS pump pulley 3/8" farther forward than the base engine configuration. This creates a very tight clearance problem between the PS pump pulley and the frame that might not work for normal production tolerances.

During this research project I heard that certain 1965 high performance small blocks with A/C and PS used a deep-groove pulley set in combination with the two rare pulleys that you show in your post. I've always wanted to see samples of these to figure out how they were configured to deal with the clearance problem, and why GM did not continue to use these same pulleys in 1966-67.

Based on the photo you show of a 3868892 PS pump pulley next to the more common standard-groove 3770509 PS pump pulley, it is clear that the 3868892 places the grove somewhat more forward than the 3770509. This suggests that the corresponding 3827843 crank pulley was stacked on top of a dual deep groove pulley such as the 3858533 used on other L79 configurations. The 3850838 dual-groove crank pulley that you mention in your post is a standard-groove pulley that was used on the base engine with A/C and PS.

Also based on the same photo in your post, the 3868892 appears to be a standard-groove PS pump pulley like the standard-groove 3770509 pump pulley next to it.

As I see it, there are three possible crankshaft pulley stack-ups that GM could have used on the 1965 L79 with A/C and PS:

1) A dual standard-groove crankshaft pulley combined with a standard-groove PS add-on pulley
2) A dual deep-groove crankshaft pulley combined with a standard-groove PS add-on pulley
3) A dual deep-groove crankshaft pulley combined with a deep-groove PS add-on pulley

Based on what I see in your photos, I think that that GM used option #2. If so, the corresponding dual crankshaft pulley would not have been the 3850838, which is a standard-groove pulley. My guess is that you would find that the 3827843 add-on crank pulley nestles snugly inside a dual deep-groove pulley such as the 3858533, while it would stick out about 1/4" from the standard-groove 3850838. I see no reason that GM would do this, but it's not impossible that they did. It's just that there would be no apparent benefit to using this instead of the PS pulleys from the base engine with A/C and PS.

So, after all the above explanation, here are my questions:

1) Can you check your files to see whether the pair of pulleys you show in your post might have been used in combination with a dual deep-groove crank pulley such as the 3858533?

2) If you have ready access to a 3858533 pulley, can you check to see if the 3827843 add-on crank pulley nestles snugly inside the 3858533 pulley?

3) Lastly, can you compare the groove width of the deep-groove 3858533 to the groove widths of the two pulleys in your posting?


My current theory is that to provide a bit more frame clearance for the PS pump pulley on the 1965 L79, GM combined standard-groove PS pulleys with a deep-groove dual crank pulley. This would preserve the high performance deep-groove pulleys for the water pump and the dual crank pulley, and would only push the PS pump pulley 1/4" forward compared to the base engine pulley set for A/C and PS. Using a full deep-groove pulley set on the L79 would push the PS pump pulley 3/8" forward compared to the base engine pulley set.

If GM did this for 1965, it is possible that they found that normal production tolerances still created occasional problems with frame clearance for the PS pump pulley. If so, this might be the reason that they switched to using the base engine pulley set for 1966-67 L79s that had both A/C and PS.

I'm hoping that you can help solve this mystery about the 1965 configuration, since it appears that I will never get my hands on samples of the very rare 3868892 and 3827843 pulleys to study in person.


Thanks,

Joe Randolph

Joe------


Yes, I finally figured this all out awhile ago but I had not posted on it yet.

First of all, the GM #3827843 add-on crank pulley was used with the GM #3858533 deep 2 groove crank pulley and NOT the GM #3850838 standard 2 groove crank pulley as I incorrectly indicated in my initial post. The 3827843 pulley will "nest" with either the 3858533 or the 3850838 but, for the 1965 with C-60 and N-40 application it was used with the 3858533 and NOT the 3850838. By the way, the standard groove GM #3751232 add-on pulley will "nest" with the GM #3850838 but it will NOT "nest" with the GM #3858533. This is partially what created the problem for GM in this case.

What I now believe happened here is that GM wanted to maintain the deep groove pulley set for the 1965 with C-60 and N-40 application. However, this could not be done with the any of the pulleys then existent. The only way they could do it with the pulleys then in their "parts bin" would have been to use the complete standard groove pulley set used for base engine and L-75 but, as I mentioned, they wanted to use a deep groove pulley set. The L-79 with C-60 and N-40 did require there be 3 crankshaft pulley grooves. So, what they did was to use an add-on crank pulley already in their parts bin, the GM #3827843 which had been used for some obscure 63-64 truck applications, in combination with a new power steering pump pulley, the GM #3868892, basically created for the 1965 with C-60 and N-40 application. The 3827843 add-on crank pulley and 3868892 power steering pump pulley are standard groove pulleys. So, when used for the 1965 L-79 with C-60 and N-40 application, a "hybrid" pulley system is created-----the 2 groove waterpump, 2 groove crank, and alternator pulleys are deep groove while the add-on, single groove crank and power steering pump pulleys are standard groove.

It is possible that the "hybrid" pulley system was used for part of or all of 1966 L-79 with C-60 and N-40. GM seems to indicate that it was but I can't say one way or the other. In any event, after that time GM forevermore went to a standard groove pulley set for all small block with C-60 applications, with or without N-40.

If I have not answered your specific questions with the above, I'll re-cap it here:

1) The 3827843 add-on crank pulley and 3868892 power steering pump pulley were definitely used with the deep groove GM #3858533 crank pulley for the 1965 L-79 with C-60 and N-40 application;

2) I have (many) GM #3858533 crank pulleys. The GM #3827843 will definitely "nest" with the 3858533. By the way, the GM #3858533 and 3751232 are still available from GM. All of the other pulleys mentioned are long-since GM discontinued.

3) The 3827843 and 3868892 are standard groove pulleys.

I might also mention that a "hybrid" pulley SET (i.e. a combination of standard groove and deep groove pulleys used on the same engine application) is VERY unusual for a Corvette application. In fact, other than the 1965 (and, possibly 1966) L-79 with C-60 and N-40, I don't know of another application.

[Joe R.]

Re: Rare Pulleys

Joe------


Yes, I finally figured this all out awhile ago but I had not posted on it yet.

First of all, the GM #3827843 add-on crank pulley was used with the GM #3858533 deep 2 groove crank pulley and NOT the GM #3850838 standard 2 groove crank pulley as I incorrectly indicated in my initial post. The 3827843 pulley will "nest" with either the 3858533 or the 3850838 but, for the 1965 with C-60 and N-40 application it was used with the 3858533 and NOT the 3850838. By the way, the standard groove GM #3751232 add-on pulley will "nest" with the GM #3850838 but it will NOT "nest" with the GM #3858533. This is partially what created the problem for GM in this case.

What I now believe happened here is that GM wanted to maintain the deep groove pulley set for the 1965 with C-60 and N-40 application. However, this could not be done with the any of the pulleys then existent. The only way they could do it with the pulleys then in their "parts bin" would have been to use the complete standard groove pulley set used for base engine and L-75 but, as I mentioned, they wanted to use a deep groove pulley set. The L-79 with C-60 and N-40 did require there be 3 crankshaft pulley grooves. So, what they did was to use an add-on crank pulley already in their parts bin, the GM #3827843 which had been used for some obscure 63-64 truck applications, in combination with a new power steering pump pulley, the GM #3868892, basically created for the 1965 with C-60 and N-40 application. The 3827843 add-on crank pulley and 3868892 power steering pump pulley are standard groove pulleys. So, when used for the 1965 L-79 with C-60 and N-40 application, a "hybrid" pulley system is created-----the 2 groove waterpump, 2 groove crank, and alternator pulleys are deep groove while the add-on, single groove crank and power steering pump pulleys are standard groove.

It is possible that the "hybrid" pulley system was used for part of or all of 1966 L-79 with C-60 and N-40. GM seems to indicate that it was but I can't say one way or the other. In any event, after that time GM forevermore went to a standard groove pulley set for all small block with C-60 applications, with or without N-40.

If I have not answered your specific questions with the above, I'll re-cap it here:

1) The 3827843 add-on crank pulley and 3868892 power steering pump pulley were definitely used with the deep groove GM #3858533 crank pulley for the 1965 L-79 with C-60 and N-40 application;

2) I have (many) GM #3858533 crank pulleys. The GM #3827843 will definitely "nest" with the 3858533. By the way, the GM #3858533 and 3751232 are still available from GM. All of the other pulleys mentioned are long-since GM discontinued.

3) The 3827843 and 3868892 are standard groove pulleys.

I might also mention that a "hybrid" pulley SET (i.e. a combination of standard groove and deep groove pulleys used on the same engine application) is VERY unusual for a Corvette application. In fact, other than the 1965 (and, possibly 1966) L-79 with C-60 and N-40, I don't know of another application.

Hi Joe:

Thanks for clarifying the relationships among these deep-groove and standard-groove pulleys. The information you provided confirms my theory about "what" happened for 65-67 C2s with A/C and PS. I can only speculate as to "why" it happened, but I think the problem may have been frame clearance for the PS pump pulley. The C2 frame kicks up right in front of the PS pump, and if the PS pump pulley is too far forward, the pulley will hit the frame.

Below is a photo showing the 3850838 dual standard-groove crank pulley next to the 3858533 dual deep-groove crank pulley. It is clear that the '533 pushes the outer groove forward. Adding a deep-groove PS add-on pulley to the '533 makes the situation even worse. A slight space savings (about 1/8") can be achieved by using a standard-groove add-on PS pulley. This is apparently what GM did for 1965.

I think the 1965 configuration is technically a good solution to the problem of limited space for the PS pump pulley. Deep-groove pulleys are used to reduce the probability of throwing a belt at high rpm. The probability of this happening is increased if the belt spans are long and/or the belt does not wrap 180 degrees around the pulley. The alternator belt and A/C belt have both of these risk factors. The PS belt has neither risk factor and is extremely unlikely to come out of the pulley groves at high rpm.

I don't know why GM didn't just use this same setup for the 66-67 C2, but maybe they found that they needed more clearance margin between the PS pump pulley and the frame to cover for normal production tolerances.

BTW, the reason I researched this topic was that I got tired of my 67 small block throwing belts at high rpm. This car has factory A/C and PS, so it had the standard-groove pulley set. The starting point was to use the deep-groove water pump pulley, crank pulley, and alternator pulley from a factory L79 with A/C but no PS. The remainder of the problem was finding compatible PS pulleys.

I managed to find two compatible deep-groove add-on crank pulleys that nest very neatly into the 3858533. One is the 3765947 that was used in some Chevy truck applications in the 1960s. The other is the 3916385 that was used on Z28 Camaros with A/C. The remaining problem was to find a deep groove PS pump pulley that would align with the deep-groove add-on crank pulley and also not hit the frame. I found that the Pontiac GTO PS pump pulley 9786900 aligns well and just barely clears the frame on my car.

A better solution that provides more frame clearance would be to use the rare 1965 PS pulley set, but those are hard to find and are not reproduced. I recall finding some other GM part number that is a physical match for the 1965 3827843 add-on crank pulley, but I never managed to find a compatible PS pump pulley like the 1965 3868892 PS pump pulley.

Thanks again for helping me to finally sort out the mystery of the 1965 PS pulley set used on L79s with A/C and PS.

[Loren L.]

Re: Rare Pulleys

I would add that the "add-on" crank pulley 3827843 on #23561 is NOT stamped with a part # but with an "S" stamping on the reverse side.

[Joe L.]

Re: Rare Pulleys

I would add that the "add-on" crank pulley 3827843 on #23561 is NOT stamped with a part # but with an "S" stamping on the reverse side.

Loren------


Yup, the 3827843 does not have a stamped part number. Seems quite strange to me, especially for a pulley used so infrequently on the assembly line. But, it may have originally had a broadcast code sticker on it.

[Larry P.]

Re: Rare Pulleys

Thanks for this very helpful post. I'm also trying to assemble a '65 L79 with the C60 & N40 options. One thing I'm still curious about is the AC compressor pulley. The TIM&JG indicates the compressor pulley is the same for L75 and L79. Unfortunately, the pulley configuration chart doesn't include the compressor. Wouldn't this setup require a different deep groove pulley for the compressor? I've been trying to find original pulleys, but that sounds like an impossible search. Hopefully, someone is producing correct repros.

[Joe R.]

Re: Rare Pulleys

Thanks for this very helpful post. I'm also trying to assemble a '65 L79 with the C60 & N40 options. One thing I'm still curious about is the AC compressor pulley. The TIM&JG indicates the compressor pulley is the same for L75 and L79. Unfortunately, the pulley configuration chart doesn't include the compressor. Wouldn't this setup require a different deep groove pulley for the compressor? I've been trying to find original pulleys, but that sounds like an impossible search. Hopefully, someone is producing correct repros.

Well, if you are trying to assemble a correct pulley set for a '65 with the odd combination discussed in this thread, you will have quite a challenge.

Regarding your question about the A/C compressor pulley, I'm not sure of the answer, but Joe Lucia probably knows.

For the two PS pulleys, Joe Lucia has confirmed that what you need is a standard-groove crank pulley that nests correctly with the double deep-groove 3858533 pulley, and a standard-groove pump pulley that aligns correctly with the corresponding crank pulley.

Other than the 1965 part numbers that Joe Lucia has described, I have not found any other pulleys that are an exact fit. However, among the miscellaneous pulleys that I accumulated during my research on this problem, I found two pulleys that come close. I don't know what their original applications were, but they have what appear to be GM part numbers.

A standard-groove add-on pulley in my collection with the part number 14023153 nests pretty nicely with the 3858533 dual deep-groove crank pulley. Its base fits well enough to mate with the two locating collars in the 3858533, but the bottom surface leaves a gap of about .050" between the bottom face of the '533 and the '153. This can be fixed with a .050" thick shim. Normally, shims are not a good idea, but in this case the add-on pulley is still properly indexed with the locating collars in the '533. And, the presence of the shim would be very difficult to detect in NCRS judging.

For the PS pump pulley, a standard-groove pulley in my collection with part number 3860457 comes very close to the proper offset for the 1965 configuration. Ideally, it would be just a tad farther forward, but its very close to correct. If the misalignment is detectable, there might be some subtle tricks you could play with the PS pump mounting bracket.

I have never actually tried this combination on an actual block and crankshaft, but I would be willing to do so if you or others here are interested. I have a block sitting on an engine stand in the garage, so it would not take much effort to actually mount the pulleys and take a look.

[Joe L.]

Re: Rare Pulleys

Thanks for this very helpful post. I'm also trying to assemble a '65 L79 with the C60 & N40 options. One thing I'm still curious about is the AC compressor pulley. The TIM&JG indicates the compressor pulley is the same for L75 and L79. Unfortunately, the pulley configuration chart doesn't include the compressor. Wouldn't this setup require a different deep groove pulley for the compressor? I've been trying to find original pulleys, but that sounds like an impossible search. Hopefully, someone is producing correct repros.

Larry------


The only compressor pulley I can find any record of that was ever used on a 1965 Corvette was the GM #5914745.

[Joe L.]

Re: Rare Pulleys

Well, if you are trying to assemble a correct pulley set for a '65 with the odd combination discussed in this thread, you will have quite a challenge.

Regarding your question about the A/C compressor pulley, I'm not sure of the answer, but Joe Lucia probably knows.

For the two PS pulleys, Joe Lucia has confirmed that what you need is a standard-groove crank pulley that nests correctly with the double deep-groove 3858533 pulley, and a standard-groove pump pulley that aligns correctly with the corresponding crank pulley.

Other than the 1965 part numbers that Joe Lucia has described, I have not found any other pulleys that are an exact fit. However, among the miscellaneous pulleys that I accumulated during my research on this problem, I found two pulleys that come close. I don't know what their original applications were, but they have what appear to be GM part numbers.

A standard-groove add-on pulley in my collection with the part number 14023153 nests pretty nicely with the 3858533 dual deep-groove crank pulley. Its base fits well enough to mate with the two locating collars in the 3858533, but the bottom surface leaves a gap of about .050" between the bottom face of the '533 and the '153. This can be fixed with a .050" thick shim. Normally, shims are not a good idea, but in this case the add-on pulley is still properly indexed with the locating collars in the '533. And, the presence of the shim would be very difficult to detect in NCRS judging.

For the PS pump pulley, a standard-groove pulley in my collection with part number 3860457 comes very close to the proper offset for the 1965 configuration. Ideally, it would be just a tad farther forward, but its very close to correct. If the misalignment is detectable, there might be some subtle tricks you could play with the PS pump mounting bracket.

I have never actually tried this combination on an actual block and crankshaft, but I would be willing to do so if you or others here are interested. I have a block sitting on an engine stand in the garage, so it would not take much effort to actually mount the pulleys and take a look.

Joe------


The only add-on (other than the GM #3827843) pulleys I know of that will mate with the GM #3858533 are the GM #346290, used in PRODUCTION for most 1975-E1980, and the GM #14023153, used in PRODUCTION for most L1980-82, which you mentioned. The 14023153 also replaced the 346290 for 1975-1980 SERVICE. Actually, I do not understand why you found even a slight fitment problem when trying to mate the 14023153 to the 3858533 as that combination was used in PRODUCTION.

As far as alignment with the power steering pump pulley, that's another problem. While the 3858533 and 14023153 combination could be used on pre-1975 Corvettes, I don't think that combination would align with the pre-1975 pump pulleys. For 1975 and later, a different power steering pump was used which, in turn, required a different power steering pulley. Originally, that pulley was GM #346289 and later GM #14023175. If a 3858533 was mated with either a GM #346290 or GM #14023153 on a pre-1975 Corvette, I believe it would require using the 1975+ pump with either the GM #346289 or GM #14023175 pulleys for the crankshaft and power steering pump pulleys to align.