1965 L76 water pump 3859326

[Al H.]

I am searching for a correct water pump for my 1965 L76. I know the correct casting number should be 3859326. Recently I have seen two water pumps with the same casting number. One pump has GM 1 with letters and numbers aprox. 1/2" in length with 3859326 underneath. The stamping is centered. The other pump has GM 3 with 3859326 underneath and the letters and numbers are much smaller, aprox 1/4" in length. The stamping on this pump is in the same general location as on the GM 1 pump but off to the left about rather than centered as the GM 1 3859326. I have been told that the number 1 and 3 are mold numbers. Would one of these pumps be moer correct for my car? Any help and/or clarification would be appreciated. Thank you.

[Joe L.]

Re: 1965 L76 water pump 3859326

I am searching for a correct water pump for my 1965 L76. I know the correct casting number should be 3859326. Recently I have seen two water pumps with the same casting number. One pump has GM 1 with letters and numbers aprox. 1/2" in length with 3859326 underneath. The stamping is centered. The other pump has GM 3 with 3859326 underneath and the letters and numbers are much smaller, aprox 1/4" in length. The stamping on this pump is in the same general location as on the GM 1 pump but off to the left about rather than centered as the GM 1 3859326. I have been told that the number 1 and 3 are mold numbers. Would one of these pumps be moer correct for my car? Any help and/or clarification would be appreciated. Thank you.

Al------

Strictly speaking, the 1 and 3 are PATTERN numbers, not mold numbers. For sand castings like waterpumps, patterns are used to make the SAND MOLDS. This might be considered a small point, but I usually like to explain the difference.

In any event, pattern numbers are not judged (and should not be because no one really knows what patterns were used). However, since 1965 was about the beginning of the 3859326 casting, it could reasonably be assumed that low-numbered patterns (e.g. 1 and 3) were being used at that time.

The features that you mentioned regarding the character differences often vary from one pattern to another so I think that they're irrelevant as far as "correctness" is concerned.

Keep two things in mind:

1) Date codes for the 3859326 casting began about November, 1965. So, any 3859326 pump used for the 1965 model year should not have a date code. That's a fairly moot point, though, because I don't think you'd ever be able to find a 3859326 pump with a date code that would be correct for any 1965 (as a result of the fact that none were date coded during the 1965 model year).

2) All waterpumps for Corvettes were cast at Saginaw and have no ribs on the driver side of the pump. However, I believe that all original examples of the 3859326 were cast at Saginaw. I do not think that Tonawanda cast this pump but I could be wrong. If any were cast at Tonawanda, they will likely have the reinforcing ribs on the driver side of the pump and a "T" cast somewhere on the body of the pump.