Water Pump Date Code Format

[Mark E.]

My car's 3840960 water pump is stamped "L80 8". Or read upside down, "8 087"? The "L" looks more like an L than an upside down 7 though.

It's on the driver's side where the date code is normally.

How is this interpreted?

I looked in the JG, but didn't find anything about how to read the code.

[Larry M.]

Re: Water Pump Date Code Format

Mark:

Water pump ate coding is MDDY............where M is the month in alphabet letters, DD is the day of the month in numerals, and Y is the year is numerals. Example is C127 which translates to March 12, 1967.

For your example the L= December, the 80 could be 30, and the 8 representing 1968 or perhaps 1978. Hope this helps.

Larry

[Mark E.]

Re: Water Pump Date Code Format

Mark:

Water pump ate coding is MDDY............where M is the month in alphabet letters, DD is the day of the month in numerals, and Y is the year is numerals. Example is C127 which translates to March 12, 1967.

For your example the L= December, the 80 could be 30, and the 8 representing 1968 or perhaps 1978. Hope this helps.

Larry

It really looks like L80 not 30, so that threw me. Still looks like 80, but you're probably right.

Also, sometimes the letter "I" is skipped in month codes. So could L be November instead of December?

[Joe L.]

Re: Water Pump Date Code Format

It really looks like L80 not 30, so that threw me. Still looks like 80, but you're probably right.

Also, sometimes the letter "I" is skipped in month codes. So could L be November instead of December?

Mark-----


If it's "80", then it's a factory mistake. I kind of doubt it. I expect it's 30.

As far as the year, the GM #3940960 waterpump was used in PRODUCTION only for later 1969 and all of 1970. So, I don't see one of these pumps being manufactured as early as 1968. Also, I believe this pump was out-of-production for SERVICE by 1978. So, I do not know what to make of the year.

The "I" is usually not skipped for CASTING dates. It's skipped for many STAMPED-type date codes, though.

[Mark E.]

Re: Water Pump Date Code Format

Thanks Joe.

Maybe it's cast "L30 9" (Dec. 30, 1969), not "L80 8"? Too much paint.

[Joe L.]

Re: Water Pump Date Code Format

Mark------


I'd say L 30 9 which would be December 30, 1969 which is within the period that I would expect 3940960 waterpumps to be cast.

[Mark E.]

Re: Water Pump Date Code Format

Mark------


I'd say L 30 9 which would be December 30, 1969 which is within the period that I would expect 3940960 waterpumps to be cast.

Thanks Joe. I like your date better for a June 1970 car.

[Joe L.]

Re: Water Pump Date Code Format

Thanks Joe. I like your date better for a June 1970 car.

Mark------

I believe that the 3940960 water pump casting was probably produced only in batches which is why there is a considerable time lag between its casting and the build date of your car. By the time that the 3940960 casting came into use the short leg style waterpump was being used only for Corvette and some MD/HD truck applications. So, given that not too many units of this waterpump were going to be required for PRODUCTION needs, the Tonawanda foundry probably considered it more efficient to cast these in batches. In addition, this casting did not last very long as it was replaced by the GM #3992077 for 1971. As such, I expect that your waterpump will have a rather low pattern number since not many patterns would have been required for a casting that was relatively low volume and short-lived.

[Mark E.]

Re: Water Pump Date Code Format

Joe,

A few years ago I contacted Bill Mock, who advertises in "Driveline" and rebuilds water pumps. He said the latest 3940960 he has seen is February 9, and believes few to none were cast after this. This means later production 1970s have a wide date gap for their 0960 pump, or used a 3992077 pump.

Is this consistent with your information?

[Joe L.]

Re: Water Pump Date Code Format

Joe,

A few years ago I contacted Bill Mock, who advertises in "Driveline" and rebuilds water pumps. He said the latest 3940960 he has seen is February 9, and believes few to none were cast after this. This means later production 1970s have a wide date gap for their 0960 pump, or used a 3992077 pump.

Is this consistent with your information?

Mark------

Generally, yes. However, I doubt that any 1970's used the 3992077 casting. My guess is that they used the 3940960 from a batch run as I mentioned previously. I doubt that Chevrolet Tonawanda was too concerned about violating the "6 month rule".

What is the pattern number on your casting?

[Mark E.]

Re: Water Pump Date Code Format

The 5th edition of the JG says "1970 Corvettes as early as s/n 2077 used...3992077" and "1971 up to at least s/n 1400 used... 3940960. (p. 153)

So you're right- this is evidence GM mass produced in large batches with lots of inventory, and simultenously picked from their old 0960 and newer 2077 water pump stock for production.

[Mark E.]

Re: Water Pump Date Code Format

Mark------

What is the pattern number on your casting?

I pulled it and shipped it off for rebuilding. I'll post it when it returns.

[Joe L.]

Re: Water Pump Date Code Format

The 5th edition of the JG says "1970 Corvettes as early as s/n 2077 used...3992077" and "1971 up to at least s/n 1400 used... 3940960. (p. 153)

Mark-----


This kind of surprises me because I don't think I've ever seen a 3992077 pump with a 1970 date (even though early 1971's should show a 1970 date).

[Mark E.]

Re: Water Pump Date Code Format

Mark-----

This kind of surprises me because I don't think I've ever seen a 3992077 pump with a 1970 date (even though early 1971's should show a 1970 date).

Don't 0960 pumps use the smaller hub and bolt pattern, while 2077 pumps use the larger pattern? If so, this means 1970 used two different types of pulleys, clutches and fans depending on which pump was installed. I don't know if I've seen this either.

[Joe L.]

Re: Water Pump Date Code Format

Don't 0960 pumps use the smaller hub and bolt pattern, while 2077 pumps use the larger pattern? If so, this means 1970 used two different types of pulleys, clutches and fans depending on which pump was installed. I don't know if I've seen this either.

Mark------

Generally, yes. However, it would be possible to use a 3992077 casting and use the 65-70 bearing assembly (i.e with 5/8" pilot) and the 65-70 hub pattern or a dual pattern hub (the hub OD was the same or nearly the same for 65-70 and 71-74). So, as far as I know, the factory could have used the 3992077 casting to make up a 1965-70 pump.