1969 L71 Water pumps

[Wes G.]

Reading from NCRS Judging Guide, the 427 water pump part number is 3856284. Reading from this discussion group, they are plentyful, casting dates are not judged as they can't be seen (however in real terms should precede engine assembly date by two weeks to two months on average, but never longer than six months).
Reading in 'Corvette by the Numbers', Flint engines were supplied with Flint water pumps and Tonawanda engines with Tonawanda water pumps (having a cast "T" on them). "Long leg water pump was introduced on most Chevrolet models while the Corvette did not change water pump styles until 1971." "Big block Chevrolet engines used the 'short leg' water pump on all Passenger cars from 1965 through 1968, and on the Corvette. Pumps used after these dates were the 'long leg' design." According to one of the tables, a 1969 Corvette (early), with a 427 engine should have pump # 3856284. While the late 1969 Corvettes hould have part # 3940960. Could someone clarify what the correct water pump would be for my 1969 (Tonawanda L71), engine assembly date of July 19/69 (T0719LR), Trim Tag date of Aug 12/69? (Pump # 3856284, 'long leg', made in Tonawanda, dated 2 to 8 weeks before July 19/69?????? Does the term 'w/small shaft' mean the same as 'short leg'?
Thanks
Wes # 33239

[Craig S.]

Re: 1969 L71 Water pumps

Wes - all BB Corvettes use a short leg pump, not long leg. That refers to the distance from the mounting flanges behind the impeller to the pulley mounting flange. The "legs" on the pump are obviously longer. The small shaft refers to the diameter of the protruding portion of the shaft from the pulley mounting flange, small meant 5/8" vs the later 3/4". I believe the BB pumps all had a 3?4" shaft in the bearing section, but the nose was turned down. I think your car would use the 284 pump.....Craig

[Joe L.]

Re: 1969 L71 Water pumps

Wes-----

All Corvettes, big block and small block, used the short leg waterpump ONLY. For small blocks, there were 2 different "short leg" waterpumps----1970 and earlier and 1971 and later. That's irrelevent to big blocks, though.

Through 1968, all Chevrolet V-8 engines used the short leg waterpumps. From 1969 onward, all EXCEPT Corvette and some MD/HD trucks, used the long leg style waterpumps.

The "Flint-versus-Tonawanda" issue is applicable only to small blocks. ALL big block major components of the 65-74 period were cast, machined and assembled at Tonawanda, NY.

I would expect that your very late 1969 L-71 would have originally been outfitted with a waterpump of casting #3940960. This casting, as well as later short leg castings, are a lot less common than the '284'. That's because the 3940960 and later were used in PRODUCTION only for Corvettes and some MD/HD trucks-----by the time the 3940960 "appeared on the scene" the short leg pump was no longer used for any other Chevrolet applications. The 3940960 was used for SERVICE waterpumps for all short leg applications for awhile, though.

All 1955-70 Corvette waterpumps, big block and small block, use a 5/8" pilot (the pilot is the short length of the shaft that extends forward from the pump flange). All 1955-82 Chevrolet waterpumps for other most other applications use a 5/8" pilot, too. 1971-82 Corvette waterpumps, as well as some MD/HD trucks, use a 3/4" pilot, small block or big block.

As far as the shaft size goes (the shaft is the part that is INWARD of the flange and goes THROUGH the bearing), it's like this:

all 1955-70 small block, Corvette and otherwise------5/8"

all 1965-74 big block, Corvette and otherwise--------3/4"

all 1971-82 small block, Corvette and otherwise------3/4"

The impeller shaft (the portion of the shaft that is INSIDE the waterpump and to which the impeller is attached) for ALL chevrolet waterpumps is 5/8".