Wanted 1975 Air Injection Reaction Pump Number

[Lyle B.]

I am looking for the original part number for a 1975 Corvette (No Air) Air Injection Reaction Pump (Smog / Emission Pump). I have the superceded number but not the original. The original number is cut-off from the copying the assembly manual. The one on the car I had found out one off of a 79 or 80 vette. It has a casting number of 7817852 with a three digit code of 289. Any help would be Apreciated

[Joe L.]

Re: Wanted 1975 Air Injection Reaction Pump Number

Lyle-----

The original AIR pump for 1975 Corvettes was a one-year-only pump of GM #7817575. This pump is externally configured like the 76-78 pumps. I don't know how it differs otherwise.

By the way, the number you quote is the casting number for a COMPONENT of the pump (most likely the rear plate) and not the part number for the complete pump assembly. The part number for the complete pump assembly is rarely, if ever, found on the pump assemblies for 66-82 Corvettes.

[Joe L.]

Small Correction

I erred in my description of the 1975 AIR pump. The 1975 pump is externally configured like the 69-74 pumps. It is NOT externally configured like the 76-78 pumps even though the REPLACEMENT pump for all 72-75 pumps IS configured like the 76-78 pump. I know that seems strange, but that's how it is.

[Patrick H.]

April 3, 2005

For the definitive answer on the subject, see Joe's post of April 3, 2005.
I can recall exactly when it was, as I met him for dinner shortly thereafter (see picture below) and he told me about the post.

"I did some more resarch on this one and came up with some more accurate information. As a result of the research, I learned something that I didn't know previously, AND I corrected some mis-information that had plagued me for a long time. As it turns out, this situation with 68-78 AIR pumps is WAY more complicated than I once believed. I'm not going to cover it all here, but I will hit the "high points" and the issue of concern to you. Here's the deal:

In PRODUCTION, all 1968 Corvettes used AIR pump GM #7801512. In SERVICE, this pump was known as GM #7803947. One of these pumps was also used in PRODUCTION for 1969 Corvettes with L-88/ZL-1. These pumps have the external relief valve on the upper aluminum body of the pump.

For 1969 (except L-88/ZL-1), the AIR pump used in PRODUCTION was changed to GM #7803948. This pump has no relief valve and, in its place, has the "roundish protrusion" in the top of the "flat surface". Otherwise, the configuration of this pump is the same as the 1968 pump. However, this pump was not then-available in SERVICE. For 1969 SERVICE, the only pump EVER catalogued by GM was pump GM #7806686. This pump has the external relief valve and is identical to the 1968 pump. It became the SERVICE pump for 1968, too, when the GM #7803947 was discontinued in October, 1969.

Now for the correction which is of importance to you: in PRODUCTION, all 1969 through 1974 Corvettes which used AIR pumps used the GM #7803948. This is the pump described above with the "roundish protrusion" on the flat surface atop the pump. For 1972-74 models this is contrary to the information I provided in my original post; this is the CORRECTED information.

In late 1972, the GM #7803948 pump became available in SERVICE. However, it was catalogued by GM as the SERVICE replacement for 72+ models ONLY. Even though it was the pump used in PRODUCTION for 69-71 models, too, it was NEVER catalogued by GM as the SERVICE replacement for those models. Instead, the GM #7806686 was the pump catalogued by GM as the SERVICE replacement for all 1968-71 Corvettes until it was discontinued in 1984.

In late 1976 a very strange thing happened. At that time, the GM #7803948 was discontinued from SERVICE and replaced, for SERVICE, by the GM #7817809 pump. This is the pump used in PRODUCTION from early 1975 through 1978. This is the pump with the larger, flat surface on the upper portion of the pump as installed in Corvettes. So, after that time, the SERVICE pump for 1972-74 Corvettes became the same as that used for 75+ Corvettes even though 1972-74 Corvettes had originally used in PRODUCTION the exact same pump as used for 69-71 Corvettes. Those applications continued to be SERVICED by the GM #7806686 pump which was never used on those applications in PRODUCTION but which, presumably, would have been the more correct SERVICE pump for 1972-74 applications, too. But, that's not how it happened and that's the thing that has caused my confusion all of these years. Now, the "record has been set straight".

Now, more strangeness: the GM #7806886 pump which SERVICED all 1968-71 Corvette applications was discontinued WITHOUT SUPERCESSION in October, 1984. However, the GM #7817809, which was used in PRODUCTION for 1975-78 Corvettes and became the SERVICE replacement for 72-74 Corvettes as well as 75-78 is still available in SERVICE to this very day (for $339.87 GM list). Since 1972-74 Corvettes originally used the same pump in PRODUCTION as 1969-71 Corvettes, then the GM #7817809 should be equally useful as a SERVICE replacement for them, too. Consequently, when the 7806686 was discontinued in 1984, there could have been a supercessive reference to the 7817809. I think that the reason may involve the fact that the 7806686 became the SERVICE replacement for 1968 models in 1969, as I described above. While the 7817809 pump would have been a perfectly acceptable SERVICE replacement for 1969-71 Corvettes, it CANNOT be used for 1968 models due to the lack of incorporation of a relief valve in the pump. So, 69-71 owners were "deprived" of an available and acceptable SERVICE replacement pump so that 1968 owners would not get an incorrect pump.

In any event, I've know for years that the 7817809 could be used as a 100% functional replacement for the 69-71. It's configuration is a little different than the original pumps used for 69-71 (and, for that matter, 72-74, too, as decribed above), but it's 100% functional.

What's the FUNCTIONAL difference between the above referenced pumps? I believe that the 68-74 pumps were of 17 cubic inch displacement and the 75-78 were of 19 cubic inch displacement. If not those exact numbers, then I'm virtually certain that there was some-such difference in displacement.

Why won't the 69-78 pumps work for a 1968 model? Well, the 1968 diverter valve does not incorporate a pressure relief function. For 1968, the diverter valve functioned ONLY as a diverter valve and the pressure relief function was performed by the pump's integral valve. So, if a 1969-78 pump with no pressure relief function is used on a 1968, then the 1968 AIR system will have no pressure relief capability, at all. That's not acceptable.

Why can a 1968 style pump with pressure relief valve be used on a 1969-74 Corvette? Well, 1969+ diverter valves incorporate BOTH diverter and pressure relief functions in the valve. So, if a 1968-style pump is used, these systems then effectively have 2 relief valves which just provides more system "redundency" and no problems, at all. - Joe Lucia"

[Joe L.]

Re: April 3, 2005

Patrick-----

You know, I'm glad that you found that previous post; I was thinking about it as I drafted these responses. Now, there might be a correction to it. I now think that the 1975 pump was the GM #7817575 which is configured like the earlier pumps and not the later. I once thought that the '575' pump was configured like the later, but now I think I know better. It may also be that the '575' pump was used for earlier 1975 and changed at some point in the model year to the '809'. I tend to think, though, that the '575' was used for the entire 1975 model year, though.

[Joe L.]

Addendum

Those FRESH MONTERY BAY PRAWNS sound VERY good to me right now. My mouth is watering.

[Patrick H.]

Re: Addendum

Yes, the prawns sound far better than the leftovers I had this evening.

Sorry I won't be out this year.
Doesn't mean I don't want to be, though.

Patrick