1968-69 smog pump

[Mark #28455]

The 1968 design smog pump had a vent pressed into the top of the pump body and had a "Y" designation in the date code stamping. By later 1969 (except for L88's) the pump no longer had the vent pressed into the pump body and the date code had an "S" designation. I was under the impression that the early 1969's used the 1968 style pump.

Does anyone have any idea when this changeover occurred? Thanks for your input!
Mark

[Kent K.]

Re: 1968-69 smog pump

Mark ----
The photo below is of my AIR pump, '69 Corvette SN 726231. The top side (I suspect since it has been off since the first owner removed it) has a 1" +/- hole divided into 4 vents and a second hole approximately 3/32" dia. The only 'S' found is a styliased cast S insignia.
Hope this helps. When are you planning to visit?
Regards, Kent #6201

[Joe L.]

Re: 1968-69 smog pump

Mark-----

As far as I know, the 68 style pump with external relief valve was used ONLY for L-88/ZL-1 applications for 1969. In those cases, it was used for all of those engined cars for the 1969 model year.

I have a friend with an original owner early 1969 (early October, 1968 build) and his pump was the 1969 style. So, I'm certain that the 1969 style pump was used as of that time. However, I really believe that it was used from the start of 1969 production. I would not rule out the use of the 1968 pump, though, for very early 1969's as, functionally, it could have been used (in fact, the 1968 style pump later became the SERVICE pump for all 1968-71 applications). However, I have no reason to believe that the 68 style pump was actually used in PRODUCTION for any 1969s.

The 1968 style pump can be used on any 1969-75 application. However, the 1969-75 style pump cannot be used on a 1968 application (or a 1969 L-88/ZL-1) unless one of the 1969-75 diverter valves is also used. The 1968 and 1969 L-88/ZL-1 diverter valve does not incorporate a relief valve function as do the 1969-75 valves. So, if you use a 1969-75 pump with a 1968 diverter valve, then there is no over-pressure relief function.

[Mark #28455]

Thanks guys for the info

That makes sense now! I stumbled across a couple old smog pumps and they both had the 1968 type relief valve. They both were made in 1968 - one earlier in the year with the 1968 date stamped near the machined area, and the other at the end of May 1968 with the date stamped on the machined spot as in 1969 production. I guess that one was likely meant for a service part.

Mark