more 1978 water pump problems

[Bill Wilkins]

I got the 3 1/8" tall 3991423 BW water pump pulley for my 78 L-48 and tried to mate it to my old incorrect water pump and it rubbed against the housing. So I bought a new pump with ACD# 251-185 and GM# 12307829 on the box and the pulley rubs on this one too. 30998 and ACI are stamped on the pump. The pulley is the correct one according to the judging manual and Delco says this pump is for 78 corvettes but they don't fit. Does anyone have any ideas?

Bill

[Joe L.]

Re: more 1978 water pump problems

Bill----

First of all, the GM #3991423 IS the correct waterpump pulley for your car if your car does not have A/C.

As far as the waterpump situation goes, it's confusing to me, too. The GM #12307829 or Delco #251-185 shows as being a correct waterpump for your application. The configuration of this pump is generally correct, too, as far as I can tell. This waterpump is available through the Delco parts system only.

There is another waterpump which I show as being correct for your application, too. This one is GM #12458924 or Delco #251-501. This pump is available through the GM parts system and may or may not be available through the Delco parts system.

I don't know what the differences are between the 12307829/251-185 and the 12458924/251-501. There might be no difference, at all. I could not assure you that if you obtained the latter pump that your problems would be solved.

Notwithstanding the above, it's very possible that the castings used for current day waterpumps have changed enough in external configuration that certain pullies will interfere with the casting. Current Delco and GM waterpumps are "outsourced" pieces and they are NOT made from the same castings as originals. Basically, they are an aftermarket casting. Most of the Corvette pullies fit very close to the castings in the original PRODUCTION versions. So, if the current day castings were just a little "beefier", interference with the pulley might very well result.

I'd say that you have 2 options:

1) If the interference is minor, you could grind the casting in the areas where it occurs to relieve the interference. As I say, there was not much clearance in the originals, so if you can achieve just a little clearance, it should be about as-original;

2) Obtain a rebuilt waterpump which uses casting GM #330813. This was the waterpump casting originally used on your car. Most available rebuilds should be of this casting. If you go this route, make sure that the one you get is, though, since there could be a lot of aftermarket castings out there in the "rebuilt-world" by now. These could cause the same problems that you're having now.

[Bill Wilkins]

Re: more 1978 water pump problems

I talked to another guy late last night and he told me that those pulleys were occaisionally a little out of round and in the dealership they used to have to machine them down a little for clearance. So I sanded the back side of the pulley until it stopped grinding and now I have nearly 2mm of clearance on the housing at the closest point. I am going to run this on the advice of the chevy mechanic and if it doesn't work, well I now know where a correct rebuilt original one is. Thanks again Joe.

Bill