water pump #3782608

[Bill Wilkins]

I pulled the wrong water pump pulley off my car today to install the correct one and it rubbed on the back of the pump. The water pump has part number 3782608 and GM 7 on it and it does not have the plug in the top like the book says it should. Does anyone have an idea if this pump is a corvette water pump or what it is? Thanks

Bill

[Joe L.]

Re: water pump #3782608

Bill-----

Waterpump casting GM #3782608 was used on a LOT of Corvettes during the 1961 to 1970 period. About the only exceptions were 61-67 models with aluminum intake manifolds. ALL 1968-70 Corvette small blocks used this casting. It's hard to say whether it's correct for your car since you didn't mention what year or engine option that you have.

The only Corvettes that were ever ORIGINALLY fitted in PRODUCTION with a waterpump that had a pipe plug plugging the unused bypass fitting on the top were later 1972 to 1982 models. NONE of these originally used the 3782608 castings, though.

[Bill Wilkins]

Re: water pump #3782608

Sorry I should have said that I have a 78 L-48. What is the right pump for my car and where do I get one?

Bill

[Joe L.]

Re: water pump #3782608

Bill-----

Now I know why you had an incorrect pulley on your car. It's because you have an incorrect waterpump. ALL pumps with the 3782608 casting use a 5/8" shaft with the same size pilot. There was NEVER an bearing/shaft available for this style pump with a 3/4" shaft and pilot which ALL 1971-82 Corvettes require.

The only way to use a 71-82 waterpump pulley with the 3782508 pump (with a 5/8" pilot) is to use a 5/8"-to-3/4" bushing as an "adaptor". I ABSOLUTELY DO NOT recommend this approach for your application. Worse yet would be to attempt to use a 71-82 Corvette waterpump pulley (with a 3/4" pilot hole) with a waterpump with a 5/8" pilot without a bushing. It CAN be done if you don't mind your waterpump and fan clutch leading a "short, but exciting life" (and, maybe, putting the fan blade through your radiator as a "parting shot")

You likely have a lot of incorrect waterpump and fan-related parts on your car as a result the incorrect waterpump and pulley. It's amazing how some previous owners and their "mechanics" hash up these cars with bogus and incorrect parts. And, I'm not just talking about NCRS/NCCB incorrect parts; I'm talking about FUNCTIONALLY incorrect parts. Here's what you need:

waterpump pulley (rear), 2 groove

without A/C--GM #3991423 (GM discontinued)
with A/C-----GM #14023159 (available; GM list=$52.81) (original pulley #346299)

waterpump pulley (front, 1 groove IF required for your application)

original GM #3991425 later GM #14023158 (BOTH are GM discontinued)

fan blade assembly

without A/C--GM #3991420 (discontinued)
with A/C-----GM #469580 (available; GM list $64.21) can be used with non-A/C but not NCRS/NCCB correct for non-A/C

fan clutch

without A/C--GM #460742 (available; GM list=$192.61)
with A/C-----GM #372502 (available; GM list= 130.17)
with VO1 HD radiator----GM #12529342 (use this one if you're smart regardless of whether it's NCRS/NCCB "correct" for your application)(available; GM list= $107.26)

waterpump

The correct casting number is GM #330813. You may be able to obtain one of these from an auto parts store if you ask for a waterpump for a 1971-82 Corvette. This is, by far, the most common casting out there for 71-82 Corvette applications. If you get a rebuilt pump and IF it has a GM casting (some could be aftermarket castings), then the chances are about 99.9% that it will be the 330813 casting. Just pay the core charge; it will be minimal. If you happen to get a pump with a GM #3991399 casting, this will be INCORRECT for your car and will lack the upper bypass boss/tapping/plug. In that case, send that one to me and I'll send you a rebuilt 330813.

If, per chance, the parts counterman hands you a long leg style pump (check it before you leave the store), hand it back to him, thank him for his time, and go somewhere else where they have counter people that know what they're doing. While virtually all 69+ Chevrolets used long leg style waterpumps, Corvettes NEVER, EVER, EVER did.

You can also get a correct casting number rebuilt pump, without need to exchange a correct casting pump, from John Pirkle or Goat Hill Classics, among many others.

If you want a NEW GM pump, likely without the correct casting number but otherwise correct and NEW, then order a GM #12458924. This pump GM lists for $141.30. You can get it for less through Delco dealers.

Depending upon just how "hashed up" your overall pulley system is at this point, you may have incorrect crankshaft pulley(s), incorrect alternator pulley, and/or incorrect power steering pump and pulley.

[Bill Wilkins]

Re: water pump #3782608

I was trying to fit the parts and had already decided it had to be all right or all wrong parts for it. Just knowing that all the wrong parts were on there is killing me. So I have been slowing collecting the right ones and now I just have to get a water pump or so I think.

Thanks again Joe, I don't know what we would do without you.

Bill

[Jim S.]

Re: water pump #3782608

Dear Joe,

What pulleys should aa 66 L79 with A/C and P/S have.I currently have a 2/1 set up and the Judging manual says it should be a 3 groove .Corvette Central says they never heard of one and Paragon says they have but dont know of a number for it.

I am sooooooo confused!
Jim schwering

[Joe L.]

Re: water pump #3782608

Jim-----

If the Judging Guide specifies a 3 groove pulley for your application, then the JG is incorrect. NO 1967 Corvette with small block engine EVER used a 3 groove pulley for either the waterpump or crankshaft application. Not one. Period. As a matter of fact, I'm not aware of any small block from 1955 through 1982 that ever used a 3 groove pulley for either waterpump or crankshaft. 3 groove pullies were used for 66-67 big blocks with A/C and MOST 68-74 big blocks for the waterpump application only. That's about it for 3 groove pullies ever used on 1955-82 Corvettes.

Your application uses a 2 groove pulley for the waterpump which was GM #3890419. In later SERVICE, this became GM #3995643, which is still available. If, per chance, your car had K-19 besides the other options you mentioned, then you would use a two pulley "sandwiched" configuration of 1 TWO groove pulley at the rear and 1 ONE groove pulley at the front. Since you didn't mention K-19, I'm not going to get into that.

Your crankshaft pulley arrangement should be 1 TWO groove pulley at the rear and 1 ONE groove pulley at the front. The rear pulley was GM #3850838 which has been discontinued for many years and front pulley is GM #3751232 which was still available the last time I checked.

[Jim S.]

Re: water pump #3782608

Joe,
Thank you very much.The Numbers you gave me are exactly the ones I have!!!
I however have spent more than a few hours talking to people and looking for a 3 groove pulley as is stated on page 86 of the "Corvette Technical Information Manual & Judging Guide" Third Edition.
I now know who to go to first and I'm sure I will do so again!!!!lucky you!!lol

Thanks Again,
Jim Schwering