Characteristics of 3992077 water pumps (71-72 454)

[Mike E.]

Two questions: is the hub to which the fan clutch and pulley bolts originally 4 hole or 8 hole?
What is the proper configuration of the back? Flat, or with a reinforced stamping?

[Joe L.]

Re: Characteristics of 3992077 water pumps (71-72 454)

Two questions: is the hub to which the fan clutch and pulley bolts originally 4 hole or 8 hole?
What is the proper configuration of the back? Flat, or with a reinforced stamping?

Mike------


I've seen them with both 4 and 8 hole hubs. They might have been originally used either way. However, ANY original hub will have a 3/4" shaft hole. A 3992077 can be rebuilt into the 65-70 configuration in which case it will have a 5/8" shaft hole.

The back plate was definitely the impressed, reinforced style. That style came into use well before the introduction of the 3992077 pump and was used right through the end of 1974.

[Joe L.]

Re: Characteristics of 3992077 water pumps (71-72 454)

Two questions: is the hub to which the fan clutch and pulley bolts originally 4 hole or 8 hole?
What is the proper configuration of the back? Flat, or with a reinforced stamping?

Mike------


A little more on this now that I have some time.

The 3992077 casting was originally used for 1971-72 Corvettes, as you mention. All of these applications used a hub bolt circle of 2-1/8" AND a 3/4" pilot shaft. There never existed ANY Chevrolet application that used the smaller 1-3/4" bolt circle with a 3/4" pilot shaft. NONE. EVER. There were never any pulleys made which had a 1-3/4" bolt circle with a 3/4" pilot hole. So, it seems to me that Chevrolet installing a dual pattern hub on these pumps would be an "oxymoron". However, that does not mean they did not.

It is possible that Chevrolet once-upon-a-time used the 3992077 casting to manufacture SERVICE pumps for 1965-70 applications. I don't see any reason why they could not have used the 3992077 casting for this purpose although I have no information that they actually did. A SERVICE pump for 1965-70 applications would have required the 1-3/4" hub bolt circle or a dual pattern hub. More importantly, though, it would have required a 5/8" pilot.

In addition, it would be very possible for aftermarket rebuilders to use the 3992077 casting for 1965-70 applications. As a matter of fact, the market for the 1965-70 pump would be FAR larger than the market for the 71-72 Corvette applications since, for 1965-68, the short leg pump was used for ALL Chevrolet big block applications. So, the rebuilders would have incentive to use the 3992077 castings for non 1971-72 Corvette applications.

It's also possible that the rebuilders could have made any of the 1965-74 short leg, big block waterpump castings-----GM #3856284, 3940960, 3992077, or 386100, workable for any 1965-74 Chevrolet big block short leg application. Here's how: install a dual pattern hub, use a shaft with a 5/8" pilot, and include a 5/8"-to-3/4" bushing with the pump for use on those few applications requiring the 3/4" pilot (only 1971-74 Corvettes and some truck applications). However, I don't think that GM ever did this for any PRODUCTION or SERVICE pump.

So, what it boils down to is this: if one finds a 3992077 pump with a 5/8" pilot, that pump was NEVER originally used on any 1971-72 Corvette. If one finds a 3992077 pump with a 3/4" pilot, whether it has a single pattern or dual pattern hub, that pump MAY have been originally used on a 1971-72 Corvette.