3848904 pulley question for Joe Lucia

[Joe R.]

Hi Joe:

Do your sources show the 3848904 dual, deep-groove water pump pulley being used on any 1966 or 1967 Corvettes, possibly the L79 when equipped with A/C but no power steering?

I have conflicting information about whether the L79 with A/C and no PS used the deep-groove pulley set consisting of the 3848904 on the water pump and the 3858533 on the crank, or the standard-groove pulley set consisting of the 3890419 on the water pump and the 3850838 on the crankshaft.

My theory is that when the L79 had A/C and no PS, it used the deep groove pulley set, and when the L79 had A/C and PS, it used the standard-groove pulley set.

Note that for an A/C car, the 3848904 deep-groove water pump pulley would be preferable to the standard L79 3770245 deep-groove pulley, since the smaller diameter of the 3848904 would spin the water pump and fan faster, as was customary for other A/C pulley sets of the period.

The justification for using standard-groove pulleys on this one L79 application is that in a configuration that required three belt grooves with the PS belt in the forward-most position, the PS pump pulley of a deep-groove stack-up would hit the frame rail where the frame kicks up right in front of the pump. The triple deep-groove stack-up is 3/8 inch thicker than the triple standard-groove stack-up, and clearance in the PS pulley area is very tight.

If, in fact, the L79 pulleys were changed to a standard-groove set *only* for the unique combination of A/C and PS, it would explain the need for the unique "HP" code associated with that combination. The standard-groove pulley set appears to use a different hub spacing on the water pump, as we discussed a few weeks ago.

I'm just trying to sort out the possible reasons for some of these little mysteries. I am finding that "pulley set engineering" is more complex than it first appears, and GM's thinking behind the various combinations they used may take some digging to discern.

[Stuart F.]

Re: 3848904 pulley question for Joe Lucia

Time to rise and shine Joe. Your adoring public awaits you. I too want to see your answer on this one.

Stu fox

[Joe L.]

Re: 3848904 pulley question for Joe Lucia

Hi Joe:

Do your sources show the 3848904 dual, deep-groove water pump pulley being used on any 1966 or 1967 Corvettes, possibly the L79 when equipped with A/C but no power steering?

I have conflicting information about whether the L79 with A/C and no PS used the deep-groove pulley set consisting of the 3848904 on the water pump and the 3858533 on the crank, or the standard-groove pulley set consisting of the 3890419 on the water pump and the 3850838 on the crankshaft.

My theory is that when the L79 had A/C and no PS, it used the deep groove pulley set, and when the L79 had A/C and PS, it used the standard-groove pulley set.

Note that for an A/C car, the 3848904 deep-groove water pump pulley would be preferable to the standard L79 3770245 deep-groove pulley, since the smaller diameter of the 3848904 would spin the water pump and fan faster, as was customary for other A/C pulley sets of the period.

The justification for using standard-groove pulleys on this one L79 application is that in a configuration that required three belt grooves with the PS belt in the forward-most position, the PS pump pulley of a deep-groove stack-up would hit the frame rail where the frame kicks up right in front of the pump. The triple deep-groove stack-up is 3/8 inch thicker than the triple standard-groove stack-up, and clearance in the PS pulley area is very tight.

If, in fact, the L79 pulleys were changed to a standard-groove set *only* for the unique combination of A/C and PS, it would explain the need for the unique "HP" code associated with that combination. The standard-groove pulley set appears to use a different hub spacing on the water pump, as we discussed a few weeks ago.

I'm just trying to sort out the possible reasons for some of these little mysteries. I am finding that "pulley set engineering" is more complex than it first appears, and GM's thinking behind the various combinations they used may take some digging to discern.

Joe-----


Yes, from what I can find, the GM #3848904 waterpump pulley was used in conjunction with the 3858533 for 66-67 L-79 with C-60 and without N-40. In fact, it was somewhat of a "revelation" for me to find this, and I still have some conflicting information. However, based on what I've found, I now think this is likely the way it was.

[Joe R.]

Re: 3848904 pulley question for Joe Lucia

Joe-----


Yes, from what I can find, the GM #3848904 waterpump pulley was used in conjunction with the 3858533 for 66-67 L-79 with C-60 and without N-40. In fact, it was somewhat of a "revelation" for me to find this, and I still have some conflicting information. However, based on what I've found, I now think this is likely the way it was.

Hi Joe L.:

Thanks for looking into this. It supports my theory that GM used a deep groove pulley set on all L79 configurations *except* the L79 with A/C and PS.

My theory for why they used the standard-groove pulley set on this one configuration is that a triple deep-groove pulley set simply would not fit, due to interference of the PS pump pulley with the frame rail.

This theory also provides a possible explanation for the unique "HP" code for an L79 with A/C and PS. That configuration would use a different water pump with the flange placed 1/8 inch back from the location used for the deep groove pulley set.

By the way, in 1967 GM had in their parts bin the necessary parts to make a triple deep-groove pully set for the L79 with A/C and PS. In combination with the 3848904 water pump puley, they could have used the 3858533 dual crank pulley, plus the 3995641 deep-groove add-on pulley from the Z-28 Camaro, and the 3873847 cast iron PS pump pulley from the Z28 Camaro. These two Z28 parts place the PS belt in the third, forward-most groove.

I have all these pulleys on hand, and I have determined that the 3873847 PS pump pulley does not quite fit the Corvette application. Part of the problem is the slightly larger diameter compared to the base 3770509 PS pump pulley, and part of the problem is that this configuration places the PS pump pulley in the third groove, more forward than the other L79 configurations that used the second groove for the PS pump belt.

I have one more related question for Joe Lucia. The 3995641 deep-groove add-on pulley for the Z-28 appears to have had a predecessor part number of the same configuration, 3765947. I think this was used on some earlier full size 409 cars.

Can you tell me what years and what usage these two deep-groove add-on pulleys are shown for?


Thanks,

Joe Randolph

[Joe L.]

Re: 3848904 pulley question for Joe Lucia

Hi Joe L.:

Thanks for looking into this. It supports my theory that GM used a deep groove pulley set on all L79 configurations *except* the L79 with A/C and PS.

My theory for why they used the standard-groove pulley set on this one configuration is that a triple deep-groove pulley set simply would not fit, due to interference of the PS pump pulley with the frame rail.

This theory also provides a possible explanation for the unique "HP" code for an L79 with A/C and PS. That configuration would use a different water pump with the flange placed 1/8 inch back from the location used for the deep groove pulley set.

By the way, in 1967 GM had in their parts bin the necessary parts to make a triple deep-groove pully set for the L79 with A/C and PS. In combination with the 3848904 water pump puley, they could have used the 3858533 dual crank pulley, plus the 3995641 deep-groove add-on pulley from the Z-28 Camaro, and the 3873847 cast iron PS pump pulley from the Z28 Camaro. These two Z28 parts place the PS belt in the third, forward-most groove.

I have all these pulleys on hand, and I have determined that the 3873847 PS pump pulley does not quite fit the Corvette application. Part of the problem is the slightly larger diameter compared to the base 3770509 PS pump pulley, and part of the problem is that this configuration places the PS pump pulley in the third groove, more forward than the other L79 configurations that used the second groove for the PS pump belt.

I have one more related question for Joe Lucia. The 3995641 deep-groove add-on pulley for the Z-28 appears to have had a predecessor part number of the same configuration, 3765947. I think this was used on some earlier full size 409 cars.

Can you tell me what years and what usage these two deep-groove add-on pulleys are shown for?


Thanks,

Joe Randolph

Joe-----

The GM #3995641 pulley did not exist in 1967. It came into being in late 1970. Also, the 3995641 is not an "add on" pulley; it's a 2 groove, primary waterpump pulley. It's predecessor was GM #3848904.

GM #3765947 was a single groove, crankshaft pulley and was of the "add-on" type. It was used for 1960-64 Chevrolet light trucks with C-60. I can find no passenger car applications, at all, for this pulley.

[Joe R.]

Re: 3848904 pulley question for Joe Lucia

Hi Joe L:

My apologies, I referenced the wrong part number in my earlier post.

The single deep-groove add-on pulley for the Z-28 Camaro was the 3916385. I have not actually seen one yet, but I believe the construction is similar to the standard-groove 3751232 except that the "dish" is deeper so that it fits properly inside the dual deep-groove 3858533 crank pulley.

While searching for a 3916385, I ran across a 3765947 that the seller said was identical to the later 3916385. I can confirm that the 3765947 is a deep-groove pulley that fits perfectly inside the 3858533 dual crank pulley, and has the same 6-3/4 nominal diameter.

The seller's theory was that the 3765947 had been used in the early 1960s on some 409 configurations, but was then discontinued. When the need for an identical pulley arose for the Z-28, the part was re-introduced with the 3916385 part number.

In any event, this was his theory. That is what made me curious about what you could uncover about the useage of these two parts.

[Joe L.]

Re: 3848904 pulley question for Joe Lucia

Hi Joe L:

My apologies, I referenced the wrong part number in my earlier post.

The single deep-groove add-on pulley for the Z-28 Camaro was the 3916385. I have not actually seen one yet, but I believe the construction is similar to the standard-groove 3751232 except that the "dish" is deeper so that it fits properly inside the dual deep-groove 3858533 crank pulley.

While searching for a 3916385, I ran across a 3765947 that the seller said was identical to the later 3916385. I can confirm that the 3765947 is a deep-groove pulley that fits perfectly inside the 3858533 dual crank pulley, and has the same 6-3/4 nominal diameter.

The seller's theory was that the 3765947 had been used in the early 1960s on some 409 configurations, but was then discontinued. When the need for an identical pulley arose for the Z-28, the part was re-introduced with the 3916385 part number.

In any event, this was his theory. That is what made me curious about what you could uncover about the useage of these two parts.

Joe-----

The seller has it backwards. As I mentioned, the GM #3765947 was originally used for some 1960-64 Chevrolet trucks with C-60. It was not discontinued until March, 1981. So, it was definitely available for use on the Z-28 applications you spoke of. However, it was NOT so-utilzed.

The GM #3916385 was used for 1967-68 Camaro Z-28's with N-40 which are the only applications I can find for that pulley. The GM #3916385 was discontinued in July, 1975 and replaced by the GM #3765947.

So, the GM #3765947 was not used for any PRODUCTION passenger car application. However, it did become SERVICE for the 67-68 Camaro Z-28 application upon the discontinuation of the GM #3916385.

[Joe R.]

Re: 3848904 pulley question for Joe Lucia

Thanks Joe. There must have been something different about the 3916385 if GM decided to make a new pulley for the Z-28. However, it must not have been very different if the 3765947 was later used as a service replacement.

I have a 3765947 in-hand, and it fits just fine in the 3858533 dual deep-groove crank pulley. I found a company that sells a reproduction of the 3916385, but the part is on back order. Eventually I hope to get one of the reproductions to look at.

Thanks again for your help with researching this.