63 L76 water pump casting number

[Tracy C.]

Could someone help me with the correct water pump casting number for a Late 63 340 Hp? Should these typically be dated and are there any passenger car applications I might stumble across in a junk yard adventure?

thanks,
tc

[Joe L.]

Re: 63 L76 water pump casting number

Tracy-----

For late 1963, the casting number was likely GM #3839175 or GM #3859326. GM #3782609 was used for most early and mid build cars. All of these pumps originally used a 1/2" NPT bypass fitting on the top. Later (after 1964)versions of the 3859326 used 3/4" NPT fitting. Pre-66 versions of the 3859326 were not dated and none of the Saginaw-cast '609' or '175' pumps were dated. The '609' and '175' were primarily used only on Corvettes. The '326' was used on many applications and was sold in SERVICE for many years for all 55-70 Corvette applications. However, most of these have 3/4" bypass fitting and are dated, so they would not be strictly correct for a 63.

[Mike M.]

Re: 63 L76 water pump casting number

agree with Joe. suggest avoiding the Tonowanda-cast pumps if you intend to have the car judged. Saginaw-cast lack gusset, tonowanda have the gusset cast in the drivers side front of the pump.

[Tracy C.]

Thanks fellas, Appreciate it !! *NM*

[Joe L.]

Re: Thanks fellas, Appreciate it !!

Tracy------

When installed on the car, the waterpump casting numbers cannot be seen and are not judged, as far as I know (pretty obvious why they're not judged if they can't be seen). The configuration of all three of these pumps is similar enough that I don't think that they can be differentiated without reference to the casting number. Of course, if a Tonawanda-cast pump like Mike described with the ribs is used, then it will be easy for anyone to discern the difference, so you want to make sure that you don't use the Tonawanda pumps. Saginaw-cast pumps without the ribs are the most common and are quite easy to locate.

What CAN be seen is the upper boss on the pump and the bypass fitting. The 3/4" fitting used on later '326' pumps is a "dead-give-away" and is well known among judges. An adapter fitting is available in reproduction to reduce this fitting size from 3/4" to 1/2", the size originally used on 63 Corvettes. Eagle-eyed judges can spot the adapter, too, UNLESS one installs it in a careful and clever manner. Use JB Weld epoxy (or silver solder, if you're into "metal") to fill in the "thread gap" and dress to a smooth finish with a file and emery cloth. Then, since the water pump is painted engine orange, the finished product will "reproduce" the original configuration and no one will be the wiser.