64 L-84 water pump

[Doug L.]

Since I am rebuilding my engine and transmission I decided I should also have the water pump rebuilt. After removing the pulley and pump I looked for the casting number. It seems that my pump is an aftermarket replacement. So rather than have an incorrect (for the car) pump rebuilt I decided to buy a correct pump. A review of the archives indicates that the correct pump for my December 1963 build 1964 car is 3859326 and that there was no date code on pump until later. In looking for a pump with this casting number I found that it was used on both Corvettes and Chevy trucks. What I read was that the Corvette pump had a 1/2" diameter outlet and the truck had a 3/4" outlet. My FI manifold has a 3/4" pipe outlet below the radiator hose gooseneck. My incorrect pump has 2 small ports, one 1-1/8" diameter and one 3/4" diameter. The port exiting the side of the pump is 3/4" diameter and has a straight pipe for connection to the heater hose. The upper port has a reducer to go from the 1-1/8" opening in the pump to the 3/4" elbow to which is connected a short, 90 degree hose connected to the manifold.

So, my questions are did the '64 FI engine use the 3859326 pump with the 3/4" outlets while base engines used 1/2" outlets? Should I be looking for and using this pump with 3/4" outlets? Are the pipe fittings attached to my pump correct (with the exception of the reducer)? I'd like to put this back together correctly but have nothing to go by. None of the photos of the '64 FI engine in the Noland Adams book show that part of the engine.

Thanks in advance for any input.
Doug

[John H.]

Re: 64 L-84 water pump

Doug -

You'll find the answer on page 107 of the 5th Edition '63-'64 Judging Guide; do you have it?

The 326 pump casting was finish-machined in two different configurations - one for trucks, with a 3/4" NPT hole for the bypass fitting, and one for Corvettes, with a 1/2" NPT hole for the smaller Corvette bypass fitting.

You either have a truck pump or a Corvette pump that's been through a commercial rebuilder and re-drilled/tapped for the larger truck fitting, as that's where the volume replacement market is for that pump.

Only the L-76 and L-84 fuelie used that pump and bypass arrangement - 250 and 300hp engines didn't use a bypass.

[Doug L.]

Re: 64 L-84 water pump

Hi John,
Thanks for the information. I have not purchased a JG yet.

If I understand correctly, all Corvettes used the pump with 1/2" outlets. In that case it seems to me that I will have to install a reducer on the bypass outlet of the FI manifold. That opening on my manifold clearly has a 3/4" diameter fitting in it now. So do I need a new straight fitting (actually a reducer) for the manifold bypass that has a 3/4" threaded base but with a 1/2" outlet, plus a 90 degree 1/2" fitting for the pump? Would I then use a 1/2" ID hose in both locations? I guess the heater hose "T" fitting and the heater inlet/outlet must be 1/2" OD also?

I guess it is time to buy a JG.

[Joe L.]

Re: 64 L-84 water pump

Hi John,
Thanks for the information. I have not purchased a JG yet.

If I understand correctly, all Corvettes used the pump with 1/2" outlets. In that case it seems to me that I will have to install a reducer on the bypass outlet of the FI manifold. That opening on my manifold clearly has a 3/4" diameter fitting in it now. So do I need a new straight fitting (actually a reducer) for the manifold bypass that has a 3/4" threaded base but with a 1/2" outlet, plus a 90 degree 1/2" fitting for the pump? Would I then use a 1/2" ID hose in both locations? I guess the heater hose "T" fitting and the heater inlet/outlet must be 1/2" OD also?

I guess it is time to buy a JG.

Doug------


I think you may be confusing measured OD of the fittings with NPT size. A 1/2" NPT size is about 3/4" as-measured OD. A 3/4" NPT fitting is about 1-1/8" as-measured OD. The fittings on your pump are likely 1/2" NPT for the heater hose nipple and 3/4" NPT for the top, by-pass fitting. This has apparently been reduced to 1/2" NPT by the use of a threaded reducer.

The original pumps used on Corvette small blocks that used external bypass (like all L-84) used a pump with 1/2" NPT bypass fitting. These pumps of ANY casting number are very difficult and expensive to find. Cleverly done, a much more common casting with a 3/4" NPT bypass fitting can be converted to 1/2" NPT in a manner that I believe no one could discern.

[Timothy B.]

Re: 64 L-84 water pump

Doug,

There is a thread about five or six months ago that goes into detail about water pumps for your year car/engine option.

It's everything you ever wanted to know plus some and a good read if asking your exact question.