Big Block Water Pump

[Rich Mullikin]

The water pump on my '69 390hp is starting to leak so I want to replace it. The water pump that is on the car is a #284 with a 1971 date. Looking into the more popular vendors they all describe the big block water pumps as short and long models. Can someone give me a description of the difference so that I make sure that I am seeking out the right item. My car was assembled in the first week in December of 1969. I do have the original fan clutch (although it is not on the car), can this be of help to me to figure out which type I need?

Any help would be appreciated.

[Joe L.]

Re: Big Block Water Pump

Rich----

With respect to Mark IV water pumps, the "short" leg design was used on all car lines from 1965 through 1968. After 1968, all Corvettes continued to use the "short" leg style until end of Mark IV installation in 1974. Most Chevrolet passenger cars from 69-up with Mark IVs used the "long" style pump. So, for Corvettes, it's easy; ALL use the "short" leg style. The same is true for small blocks.

The 3856284 casting water pump is considered by many, including NCRS, to be the correct casting number for your car. However, I believe that later 69 Corvettes with 427s could have used the 3940960 casting pump and your car is a VERY late build 69. This is a very similar casting to the 3856284. Very few people may agree with me on this one, but Alan Colvin does. Anyway, if you can obtain an appropriately dated '284' pump, that's probably your safest bet. '284s' are easier to find than '960s', anyway.

Other than the casting number, your pump will use the "small" bolt pattern hub(1-1/4" center-to-center hole spacing) although most rebuilt pumps come with the dual bolt pattern hubs. Also, your pump shaft will have a 5/8" diameter pilot shaft(the short section of the shaft which extends above the hub flange and center-locates the fan clutch). This arrangement was used from 1965-1970. 1971-1974 Mark IVs used the "large" bolt pattern hub(1-1/2" center-to-center)and 3/4" diameter pilot.

[Joe L.]

Re: Big Block Water Pump

Rich----

With respect to Mark IV water pumps, the "short" leg design was used on all car lines from 1965 through 1968. After 1968, all Corvettes continued to use the "short" leg style until end of Mark IV installation in 1974. Most Chevrolet passenger cars from 69-up with Mark IVs used the "long" style pump. So, for Corvettes, it's easy; ALL use the "short" leg style. The same is true for small blocks.

The 3856284 casting water pump is considered by many, including NCRS, to be the correct casting number for your car. However, I believe that later 69 Corvettes with 427s could have used the 3940960 casting pump and your car is a VERY late build 69. This is a very similar casting to the 3856284. Very few people may agree with me on this one, but Alan Colvin does. Anyway, if you can obtain an appropriately dated '284' pump, that's probably your safest bet. '284s' are easier to find than '960s', anyway.

Other than the casting number, your pump will use the "small" bolt pattern hub(1-1/4" center-to-center hole spacing) although most rebuilt pumps come with the dual bolt pattern hubs. Also, your pump shaft will have a 5/8" diameter pilot shaft(the short section of the shaft which extends above the hub flange and center-locates the fan clutch). This arrangement was used from 1965-1970. 1971-1974 Mark IVs used the "large" bolt pattern hub(1-1/2" center-to-center)and 3/4" diameter pilot.

[Rich Mullikin]

Re: Big Block Water Pump

Joe,

Thanks for the response, it was a big help!

[Rich Mullikin]

Re: Big Block Water Pump

Joe,

Thanks for the response, it was a big help!