Interpreting smog pump dating

[Monte M.]

Re: Interpreting smog pump dating

Food for thought guys. The early 1972 smog pump 7801149, with the 1968 style pressure relief valve on top, has the numbers "09211W".

There is our "W", but it is used in a non conventional application. It came off of an early 1972 LT-1.

[Mike E.]

Re: Interpreting smog pump dating

FWIW--my 67 base motor AIR car's pump (correct T style fitting) is 11271S and the car is a mid-May car. Can't tell you it's the original because it wasn't on the car when I got the car. Attached photos are of another pump that came with the car (a previous owner was GM parts man) Cast 1967. Dated 1971 (about the same time as the box! The pump on the car would not fit Mark Gorney's research (which I value a lot), the pump in the box would.P3131845.jpgP3131847.jpgP3131850.jpgP3131852.jpg

[Terry M.]

Re: Interpreting smog pump dating

Paul------

The alpha character at the end of the series represents the pump model.

1966-67= "A" (and, possibly, other codes, too)

1968 (GM #7803947 with relief valve)= "Y"

1968 and 1969 L-88/ZL-1 (GM #7806686 with relief valve)= "S"

1969-74 (GM #7803948 no external relief valve)= "S"

1975 (GM #7817575 no external relief valve)= "S"

1976-78 (GM #7817809 no external relief valve; different configuration than 69-75)= "S"

The first 3 digits of the stamped code represent the julian date. The 4th digit represent the last day of the year. The 5th digit may be a shift identifier. The final alpha character is pump model.

Attached are photos of an NOS GM #7806686. Note that the first 3 digits of the code are very lightly stamped and may be difficult to read.

Joe,

No offense, but all those differences and still a model "S"? Four different part numbers and still model S? That just doesn't seem right. We are missing something, I think.

Just to ass something positive, I have seen quite a few 1968 pumps that are not stamped on the machined flat, but adjacent to it. Not a big deal; just different.

[Matthew G.]

Re: Interpreting smog pump dating

Mike, I would keep your "S" pump on there. Until there is DEFINITIVE resolution on the P (which probably will never happen), your next priority might need to be the date. (The 71 is more than likely a replacement). However, I'm still trying to figure out why anyone back then would have wanted to replace one? Seems like the first thing they wanted to pull off.

[Joe L.]

Re: Interpreting smog pump dating

Joe,

No offense, but all those differences and still a model "S"? Four different part numbers and still model S? That just doesn't seem right. We are missing something, I think.

Just to ass something positive, I have seen quite a few 1968 pumps that are not stamped on the machined flat, but adjacent to it. Not a big deal; just different.

Terry-----

I think the difference is in the part number, not the model. I am not surprised, at all, that some 1968 and all 1969-75 used the same model pump. The basic pump (i.e. the "model") was the same. The one that surprises me, though, is the 76-78. I would think that would have been a different model because that pump is somewhat different and, I believe of a slightly different CID displacement (17 CID for 68-75 and 19 CID for 76-78). However, the 76-78 pump is functionally interchangeable with 69-75 so maybe that's enough so that the model designation remained the same.