C3 Rebuild

[Terry M.]

Re: C3 Rebuild

Dominick-------

Before you even consider having what you have rebuilt, you need to be sure that what you have is functionally correct and/or original. So, I'm going to do a little AIR system primer hear for the possible edification of you and others. Since there are quite a few photos, I'm going to make this a "3 part" series:

The 1969 AIR pump:

The AIR pump used for most, if not all, of 1969 was GM #7803948. This same pump was used through 1974 for both small blocks and big blocks except L-88/ZL-1. It was available in SERVICE until January, 1976 when it was replaced by GM #7817809. Earlier examples of the 7803948 pump have a "white" centrifugal filter ("fan"); later have a black centrifugal filter. Otherwise, the pumps are identical. These pumps have no pressure relief valve as do all previous 1966-68 pumps. From 1969 onward the pressure relief valve was incorporated into the diverter valve assembly. The pump shown below, an NOS GM #7803948 [not for sale], is date coded 24132S. This decodes to the 241st day of 1973 (8/29/73), 2nd shift and pump model "S". Your pump, if original, should have a white centrifugal filter but be otherwise identical to this pump.

Joe
Very nice job (as usual). I'm looking forward to the "rest of the story." I must point out there is a lot of work involved in this. My hat (If I wore one) is off to you. Thank you.

[Joe L.]

Re: C3 Rebuild

More about AIR system pumps:

The 1966-67, 1968 and 1969 L-88/ZL-1 pumps incorporated a pressure relief valve. The valve can be seen in photos I previously posted but I will show better close-up photos of the valve below. The valves for the 1966-67 and 1968/1969 L-88/ZL-1 pumps were similar but are not interchangeable. However, the plugs installed to set the relief pressure of the particular pump are interchangeable. The all 1968 and 1969 L-88/ZL-1 pumps were used across a very wide variety of GM vehicles for the 1968 model year. They are all identical except for the installed pressure relief valve plug. There were at least 5 and, possibly, 7 different plugs used. These pumps used to be very common in the rebuilt aftermarket and used markets. However, which plug was installed was a "crapshoot" but virtually nobody paid much attention to this feature. ALL 1966-67, 1968, and 1969 L-88/ZL-1 Corvettes as well as many other Chevrolet models used a BLACK plug. This plug is 0.310" in length (must be removed to measure length but if it's black one knows it's the correct plug). I pictured 5 of the plugs in a previous post in this thread.

The plugs seat against the relief valve spring cap and effectively pre-load the spring, controlling relief pressure. In the photos below, you will note the relief valve without an installed plug in an NOS pump and another rebuilt pump with an installed plug. However, the plug appears to be green so this is not originally a Corvette pump.

How functionally important is a relief valve with the correct plug? I don't know but I expect it's not really all that important from a FUNCTIONAL perspective.


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[Joe L.]

Re: C3 Rebuild

Even more on AIR system pumps:

As I previously described and pictured, all 1969-74 Corvettes except 1969 L-88/ZL-1 used AIR pump GM #7803948. This pump uses no integral pressure relief valve but, instead, has the pressure relief function incorporated into the diverter valve. For 1975 only, a new part-numbered pump was used. This was GM #7817575. It is externally identical to the 7803948 and I do not know how it otherwise differs. Both the 7803948 and 7817575 are 17 cubic inch displacement pumps. The NOS example pictured [not for sale] is dated 02254S which decodes to August 12, 1974. It's also an "S" model pump, same as the 7803948.


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[Joe L.]

Re: C3 Rebuild

Yet even more on AIR pumps:


For 1976 a new design AIR pump was used, GM #7817809. This pump was used from 1976 through 1978. GM says that it will SERVICE 1972-78 but it will actually SERVICE 1969-78. Of course, it's not of the correct configuration for 1969-75 but it will fit and function perfectly. It is a 19 cubic inch pump but is still considered an "S" model pump. This NOS example [not for sale] is dated X32541S or November 20, 1974. Given the date, it must have been used on some other GM vehicles prior to 1976.


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disregard the photo of the u-joint. I accidentally included it, tried and failed to delete it

[Mark F.]

Re: C3 Rebuild

Yet even more on AIR pumps:...

Hi Joe,

You are a fount of knowledge ! thank you so much for sharing !

I notice in your photos that the air pumps and kits were apparently made by Saginaw Steering Gear...

A few questions if you don't mind...

1. What other products (other than steering-related and A.I.R.-related parts/assemblies) did Saginaw Steering Gear make?
2. Did Saginaw Steering Gear have their own casting facilities ? - Or did those cast iron and cast aluminum parts come from some other Central Casting facility back in those years ?

[Joe L.]

Re: C3 Rebuild

Hi Joe,

You are a fount of knowledge ! thank you so much for sharing !

I notice in your photos that the air pumps and kits were apparently made by Saginaw Steering Gear...

A few questions if you don't mind...

1. What other products (other than steering-related and A.I.R.-related parts/assemblies) did Saginaw Steering Gear make?
2. Did Saginaw Steering Gear have their own casting facilities ? - Or did those cast iron and cast aluminum parts come from some other Central Casting facility back in those years ?

Mark------


In addition to the complete range of steering gear components, Saginaw Division manufactured the AIR system pumps and manual transmissions, both 3 speed and 4 speed. They may have manufactured other components that I am unaware of.

I am unaware that Saginaw Division operated metal casting operations but it's possible that they did as part of their factory complex in Saginaw. While several GM cast iron foundries once existed in Saginaw, they were not part of Saginaw Division. Those were initially operated by Chevrolet and, later, became part of GM's Central Foundry Division. The AIR pump major components were definitely cast by Central Foundry Division. You will note the "wagon wheel" symbol and "D" seen on the rear plate of all the pumps I pictured. This identifies the foundry as "Central Foundry--Danville", GM's former malleable/ductile iron foundry located near Danville, IL, long since closed and demolished. The main aluminum housing often has "CFB" cast in the area under the fan. This denotes "Central Foundry Bedford, GM's permanent mold/die casting foundry in Bedford, Indiana (still in operation today).

[Mark F.]

Re: C3 Rebuild

Mark------...Those were initially operated by Chevrolet and, later, became part of GM's Central Foundry Division. The AIR pump major components were definitely cast by Central Foundry Division. You will note the "wagon wheel" symbol and "D" seen on the rear plate of all the pumps I pictured. This identifies the foundry as "Central Foundry--Danville", GM's former malleable/ductile iron foundry located near Danville, IL, long since closed and demolished. The main aluminum housing often has "CFB" cast in the area under the fan. This denotes "Central Foundry Bedford, GM's permanent mold/die casting foundry in Bedford, Indiana (still in operation today).

Thanks for that background, Joe, - All that Saginaw "complex" approach makes sense...

I guess Ford had similar geographical / manufacturing concepts. Their Casting Division Plants were frequently co-located with assembly plants using the larger castings they produced. Cleveland Casting (10 casting lines) was co-located with Cleveland Engine Plant No. 1 and Cleveland Engine Plant No. 2; Windsor Casting was co-located with Windsor Engine Plant; and Dearborn Specialty Foundry (don't think they cast engine blocks when I was there '77-'81) was in the Rouge co-located with the old Dearborn Engine Plant. Sometimes concepts of efficient production and design don't vary between those huge competitors at the time as much as some folks might think.