1964 Corvette L76 undated water pump uncertainty; 3782609 vs 3839175 vs 38559326
08-17-2012, 11:01 AM
#1
Team Owner
Thread Starter
1964 Corvette L76 undated water pump uncertainty; 3782609 vs 3839175 vs 38559326
NOTE: So as to not hijack the "Water pump casting numbers - 1963" thread which is complete for the OP, I began this 1964 L76 undated water pump thread.
I'm thoroughly confused on which water pump was factory installed on early 1964 Corvettes with L76 SHP engines (mine is October 1963 assembled).
3782609
3839175
38559326
In the other thread, Donald #31176 posted:
Bill Mock (via Alan D. citation) on NCRS forum said this:
This is how I read that for undated water pumps:
3782609: mid-1961's to early-1963's 340 HP 360 HP
ending with engine assembly date Dec. 1962
3859326: mid-1963's 340 HP 360 HP, 1964's 365 HP, 1965's 365 HP, early 1966's 350 HP
ending with engine assembly date Oct. 1965
3839175: some 1964's with 365 HP only
Here's the confusion given the above 2 posts:
If 3782609 was replaced by 38559326 in January 1962, but 38559326 was not cast until late 1964, which would be the correct one for a 1964 Corvette with 365 HP engine assembled October 1963?
I'm thoroughly confused on which water pump was factory installed on early 1964 Corvettes with L76 SHP engines (mine is October 1963 assembled).
3782609
3839175
38559326
In the other thread, Donald #31176 posted:
There was a discussion on this subject on the NCRS TB a few years ago.
One camp concluded that the #3782609 casting was used exclusively on SHP Corvette engines from 61-mid 64. The argument was casting #3859326 was not cast till very late in 1964 and used at the beginning of the 65 model year. Casting #3839175 some say was used in limited quantities late in the 64 model year.
One camp concluded that the #3782609 casting was used exclusively on SHP Corvette engines from 61-mid 64. The argument was casting #3859326 was not cast till very late in 1964 and used at the beginning of the 65 model year. Casting #3839175 some say was used in limited quantities late in the 64 model year.
The 3782609 water pump was used on 1961 Corvettes(except early 1961's which used the top tank radiator where the 3736493 water pump was used) and 1962 Corvettes and also 1963 Corvettes with the 340hp327 and 360hp327 thru December 1962 engine assembly dates when the "609" water pump was replaced with the 3859326 undated water pump. The undated "326" water pump was used on the HP 327 engines with bypass thru October 1965(early 1966 with 350hp327) and then the "326" water pump was date coded starting in November 1965. In 1964 the 365hp327 and 375hp327 engines randomly used the "175" undated water pump(about 10%) instead of the "326" undated water pump.
3782609: mid-1961's to early-1963's 340 HP 360 HP
ending with engine assembly date Dec. 1962
3859326: mid-1963's 340 HP 360 HP, 1964's 365 HP, 1965's 365 HP, early 1966's 350 HP
ending with engine assembly date Oct. 1965
3839175: some 1964's with 365 HP only
Here's the confusion given the above 2 posts:
If 3782609 was replaced by 38559326 in January 1962, but 38559326 was not cast until late 1964, which would be the correct one for a 1964 Corvette with 365 HP engine assembled October 1963?
Last edited by ifitgoesfast; 08-17-2012 at 11:08 AM.
08-17-2012, 11:22 AM
#2
Team Owner
Thread Starter
time line, according to Bill Mock
Leaving out 3839175 (1964 L76 SHP models only), here's the timeline according to Bill Mock's post:
engine assembly dates, undated water pumps:
late 1960 to Dec. 1962: 3782609 (GM 1 - 4 S 1 - 4)
Jan. 1963 to Oct. 1965: 3859326 (GM 1 - 4)
engine assembly dates, undated water pumps:
late 1960 to Dec. 1962: 3782609 (GM 1 - 4 S 1 - 4)
Jan. 1963 to Oct. 1965: 3859326 (GM 1 - 4)
08-17-2012, 11:43 AM
#3
Le Mans Master
I would go with Bill Mock's analysis. He has been studying these pumps for decades. Find a 326 with 1/2" bypass outlet, or with 3/4" outlet and bush it down, preferably with no date. If it has a date, grind it off, and massage to look as original, rebuild, paint and bolt it up.
regarding RY below,
if you have to settle for the 3/4", you have to insert bushing and cut it off flush, hog it open a bit with a 1/2" IPS tap, dress the top surface of the boss to make the bushing disappear and replicate original surface texture. Pretty easy process and after paint, no judge will spot it.
regarding RY below,
if you have to settle for the 3/4", you have to insert bushing and cut it off flush, hog it open a bit with a 1/2" IPS tap, dress the top surface of the boss to make the bushing disappear and replicate original surface texture. Pretty easy process and after paint, no judge will spot it.
Last edited by 65hihp; 08-17-2012 at 06:02 PM.
08-17-2012, 12:59 PM
#4
Melting Slicks
Member Since: Feb 2011
Location: Syracuse, NY and Clearwater, FL
Posts: 2,076
Received 196 Likes
on
144 Posts
What I have to offer will only add to the confusion, so I will try to limit the information.
1) The casting number is not visible with the pulley installed.
2) There is a difference you can see: 326 has a flat in front of the bypass fitting, 609 is round.
3) I have a L76 assembled in March '63. My car is very original and unmolested, with ample evidence that the "609" water pump has never been removed. This is a discrepancy from Bill Mock's statement.
4) The LAST thing I would do is buy a 3/4". The first thing Judges look for is a bushing.
1) The casting number is not visible with the pulley installed.
2) There is a difference you can see: 326 has a flat in front of the bypass fitting, 609 is round.
3) I have a L76 assembled in March '63. My car is very original and unmolested, with ample evidence that the "609" water pump has never been removed. This is a discrepancy from Bill Mock's statement.
4) The LAST thing I would do is buy a 3/4". The first thing Judges look for is a bushing.
