Smog pump bracket adjuster slot size?

[Douglas P.]

All,

A current eBay listing for smog pump adjuster brackets indicates that 1968 and early 1969 (though November '68 production) 427's utilized a bracket with a short adjustment slot and later cars had a slot that was longer. I do not see reference to this difference in either the 68-9 JG or in the 1969 Stingray Guidebook. Could someone please confirm that the early '69 cars (I'm specifically interested in the L71 application, but info for any BB application is appreciated) had the short slot adjuster?

Thanks,

Doug

[Dan C.]

Re: Smog pump bracket adjuster slot size?

I am trying to figure the same thing out. I have an early 68 L36 (October 1967 production) with the original smog system having a long adjustment slot. I am now restoring a very late 68 L36 (August 1968 production) with a short slot - which makes it difficult to remove the belt. Can anyone why there is a difference and when the change was made? Thanks!

[Joe L.]

Re: Smog pump bracket adjuster slot size?

I am trying to figure the same thing out. I have an early 68 L36 (October 1967 production) with the original smog system having a long adjustment slot. I am now restoring a very late 68 L36 (August 1968 production) with a short slot - which makes it difficult to remove the belt. Can anyone why there is a difference and when the change was made? Thanks!

Dan and Doug-------


There were 2 different AIR pump braces used for big blocks during the 1968-74 period. These are as follows:

GM #3921903----this is the "long slot" brace; this part number implies a late 1967 release.

GM #3955221----this is the "short slot" brace; this part number implies a late 1968 or early 1969 release.

According to GM, the 3921903 was used for 1968, the 3955221 used for 1969, and back to the 3921903 for 1971-74. Of course, it's very possible that the 3921903 was used for early 1969 or the 3955221 used for late 1968.

The GM #3955221 was discontinued from SERVICE in January, 1971 and replaced by the GM #3921903.

I expect that it would be very difficult to determine the originality of these braces on any existing cars due to the fact that so many big blocks have been "created" post factory and, especially, since so many Corvettes long ago "lost" their AIR systems only to have them restored to the cars much later in their life. I also expect that the "long slot" braces are far more common and available than the "short slot" as both of the braces are Corvette-only pieces.

By the way, I cannot figure out why GM would have gone to the "short slot" brace for the 1969 model year.

[Dan C.]

Re: Smog pump bracket adjuster slot size?

Joe, Thank you for your quick response. Do you think that the 3955221 short slot brace could have been on the late 1968 models or do you think it was released for 1969 models made in late 1968? My 1968 with the short slot brace has a pump dated July 19, 1968 and the car shipped August 12, 1968, which I believe was the last day of production. Thank you! Dan

[Joe L.]

Re: Smog pump bracket adjuster slot size?

Joe, Thank you for your quick response. Do you think that the 3955221 short slot brace could have been on the late 1968 models or do you think it was released for 1969 models made in late 1968? My 1968 with the short slot brace has a pump dated July 19, 1968 and the car shipped August 12, 1968, which I believe was the last day of production. Thank you! Dan

Dan-------


I think it's possible the "short slot" brace was used for late 1968. End-of-model year and beginning-of-model year variances for a part like this are very possible. However, given the 3955221 part number, I think it's unlikely (but still possible).

[Dan C.]

Re: Smog pump bracket adjuster slot size?

Joe, Thank you for the clarification. Dan

[Terry M.]

Re: Smog pump bracket adjuster slot size?

Joe, Thank you for your quick response. Do you think that the 3955221 short slot brace could have been on the late 1968 models or do you think it was released for 1969 models made in late 1968? My 1968 with the short slot brace has a pump dated July 19, 1968 and the car shipped August 12, 1968, which I believe was the last day of production. Thank you! Dan

Dan
The last date (on the trim tag) that I have observed for 1968 production is M09. That is Friday August 9, 1968. It is very possible, even probable, a car with that trim tag date may not have been shipped from St Louis until August 12th. That is a Monday. The higher the VIN the more likely the car would not have been completed until the following Monday and maybe even Tuesday August 13th.

I have observed an inordinate nimbler of Corvettes with the M09 date. That makes me think that they may have simply stopped advancing the date stamp for the trim tag and continued building cars in order to clear parts or meet production goals. I think it is not just parts that get wierd toward the end of production.

[Dan C.]

Re: Smog pump bracket adjuster slot size?

Terry, Thank you for your comment on the M09 stamp and things getting weird toward the end of 68 production. My car is #28496 and stamped M09. The shipping document states Monday, August 12. When you say they were "clearing parts or meeting production goals" that may be a the best explanation for the oddities I am seeing here. Mine is a 44000 mile unrestored convertible, bronze/tobacco full of patina. The door panels are dated July and August of 1968 and show virtually no wear but the driver door was originally dark orange an dyed tobacco. It appears to be a very neat job although the orange is now showing through with scuff marks. No other interior panels are dyed tobacco, just this one panel. Other oddities include a 1969 dash gauge bezel, 1969 windshield moldings, 3931063 heads dated July '68, 1111926 distributor with a July '68 date.

I too have not found any 68 cars after M09 and have been thinking that I had a "last day survivor" finished on Friday and shipped on Monday. That's not the case if you are aware of cars delivered Tuesday the 13th or later. Please share any late ship dates or other M09 observations. I really enjoy learning the back story on these cars! Thanks, Dan

[Terry M.]

Re: Smog pump bracket adjuster slot size?

Terry, Thank you for your comment on the M09 stamp and things getting weird toward the end of 68 production. My car is #28496 and stamped M09. The shipping document states Monday, August 12. When you say they were "clearing parts or meeting production goals" that may be a the best explanation for the oddities I am seeing here. Mine is a 44000 mile unrestored convertible, bronze/tobacco full of patina. The door panels are dated July and August of 1968 and show virtually no wear but the driver door was originally dark orange an dyed tobacco. It appears to be a very neat job although the orange is now showing through with scuff marks. No other interior panels are dyed tobacco, just this one panel. Other oddities include a 1969 dash gauge bezel, 1969 windshield moldings, 3931063 heads dated July '68, 1111926 distributor with a July '68 date.

I too have not found any 68 cars after M09 and have been thinking that I had a "last day survivor" finished on Friday and shipped on Monday. That's not the case if you are aware of cars delivered Tuesday the 13th or later. Please share any late ship dates or other M09 observations. I really enjoy learning the back story on these cars! Thanks, Dan

Dan
Your assessment of the shipping date of your car seems fine to me. I have no shipping information available to me for any of these late cars. I have accumulated trim tag/VIN information in an effort to determine the St Louis work schedule. For example: One shift or two? Work Saturday? Work between Christmas and New Years? While doing that other production anomalies have appeared. The unusual build at the end of 1968 production is just one of them.

You have made some very interesting observations about your car. It sounds unique. Enjoy.