3940960 BB Water Pump

[Craig S.]

Dual drilled flange? I would think this means it is rebuilt not NOS......back in that vintage.....Craig




BB Pump

[Joe L.]

Re: 3940960 BB Water Pump

Craig------

It's a new and not rebuilt pump. For one thing, you could never purchase a rebuilt pump through the GM parts system (in a GM parts system box, like the one pictured). All GM-available rebuilt waterpumps were Delco parts system-only pieces (and, supplied in Delco boxes). Although it can't be seen well enough in the photo to read, the part number on the box is likely GM #3957982. I have several of these [none for sale] and all are GM casting #3940960 pumps.

Second, most SERVICE GM waterpumps had the dual bolt pattern hubs. Some PRODUCTION pumps used them, too. For PRODUCTION, the pumps were generally built with only the bolt pattern required for the particular application. GM saved a few cents per unit by using hubs with only 4 drilled and tapped holes instead of 8. For SERVICE, though, it was cheaper to use the dual-drilled hubs than it was to have 2 different SERVICE part numbers.

At times, the dual drilled hubs were used for PRODUCTION, too. Probably to either minimize the number of PRODUCTION part numbers or because the single drilled hubs ran short.

The strange thing with the dual drilled hubs on "284" and "960" casting pumps is that I don't know of any application that used the short leg pump (which both of these are) with a 5/8" pilot and a large bolt pattern hub. There may have been some, though, although there were NO Corvette applications.

The "284" and "960" casting pumps with short legs, dual pattern hubs, and 5/8" pilots CAN be used for 1971-74 Corvette applications (using the large bolt pattern) IF a precision 5/8"-to-3/4" bushing is also used. These bushings are supplied with some aftermarket and/or rebuilt waterpumps. However, they were not supplied with a GM parts system NEW waterpump. So, I don't see the need for the dual pattern hubs on these pumps. But, they had them. That's for sure.

[Craig S.]

Re: 3940960 BB Water Pump

Thx Joe - what confused me was the date was supposedly in 1969, and I was thinking the larger pattern was later on in the early seventies. This made me think it was at least a vintage newer than the seller states....maybe 1979 instead of 69? Just curious......as always I knew you would have a good story on the part!....Craig

[Joe L.]

Re: 3940960 BB Water Pump

Craig-----

I don't know of any usage of the larger hub bolt pattern prior to 1971, Certainly, it was not used on any Corvettes. Nevertheless, SERVICE pumps of the era usually used the dual pattern hubs, regardless. All of the NOS pumps that I have with 3940960 castings have the dual bolt pattern. All of the ones that I have show 1969 or 1970 casting dates. I don't think that this pump casting was used or manufactured after 1970, although it's possible that it was.

I always thought that all of these big block pumps were cast, machined and assembled at Tonawanda (foundry, engine plant). However, this one may not have been. The fact that it has a 1 digit year date code and no "T" anywhere that I can see on the casting might indicate that it was manufactured elsewhere. Or, it could have been manufactured at Tonawanda without the usual features. Either way, I think that it was manufactured in 1969 and not 1979.

[Mark #28455]

date codes

I have many Tonawanda big block parts and I don't recall any prior to 1970 having a 2 digit date code.
Mark