'64-65 A/C small block rear support bracket ??

[Wayne M.]

Need your opinion on this item I picked up at Carlisle. This is the horizontal bracket that bolts to the RH exhaust manifold, to which you attach the front and rear supports/brackets for the compressor. Note the eyelet (complete with surface rust) which was machined AFTER painting, similar to brake calipers; same on the forward eyelet. I believe this part is NOS.

Notice the casting #; 3841696, which is the same # as is in the '65 AIM as well as the '65 P&A30 catalogs. However, the '67 P&A30 [Gr. 9.171] shows # 3878222 for '66 and '67. I believe the difference is that there is a circular "cut-out" in the area where the pencil points to in the photo. And I think that this change in design is to allow an A.I.R. (K19 option) injection tube to attach to the exhaust manifold.

All repro catalogs show this part with the indentation. BTW, my early '65 C60 car has the bracket as shown in photo.

So I'd appreciate comments on whether the proper (pre-A.I.R.) support is as shown in the pic., and that the latter indented style is for '66-up. I realize that the TM&JG's don't get into this detail (or they'd be as thick as a phone directory).

[Peter L.]

Re: '64-65 A/C small block rear support bracket ??

Wayne - Nice piece. Because inquiring minds want to know, I looked at several of these supports including the one on my early 67 and all of the p/n 3878222 supports have the semi-circular "cut out" cast into the part that appears to line up with where the A.I.R. plumbing would attach to the exhaust manifold of an A.I.R. car. In examining the p/n 3878222 supports I noted that there were two different configurations in the design of the top of the 6" support section between the eyelets in the bracket that the compressor front and rear brackets attach. On one configuration of the support the 6" section between the eyelets going from the front to the rear is 15/16" wide for 2-1/2" and the 3/4" wide for the rest, i.e 3-1/2". This is the configuration of the one on my 67 and could well be the first revision since it matches the design of the corresponding section on the p/n 3841696 I have and the one in your picture. On the second configuration of the support the 6" section between the eyelets going from the front to the rear is 15/16" wide for 2-1/2", then 5/8" for 1-1/4" and the 3/4" wide for the rest, i.e 2-1/4".

In addition, I found a p/n 3841696 bracket and it looks identical to the one in your picture. It has a piece if masking tape on it with 64 283 327. This piece has never been installed and I believe it to be NOS. It has the 3841696 and GM embossed on the web like your but has a B in a circle and a 5 with an underline on back side of the p/n web where yours has some marking the next web. This piece has all of the surfaces including the machined surfaces painted. Very interesting. Pete

[Joe L.]

Re: '64-65 A/C small block rear support bracket ??

Pete and Wayne------

The GM #3841696 is the rear support used for 1964-65 Corvettes with C-60. It was also used for 64-65 passenger cars. For 1966, the bracket was revised for the reason speculated and the part and casting number changed to GM #3878222. The "cut-out" was a feature of the casting and not the finish machining. The GM #3841696 support was discontinued from SERVICE in November, 1967 and replaced by the GM #3878222 for all 64-65 applications.

The GM #3878222 bracket continued to be used for Corvette small blocks with C-60 through 1974. For the 1975 model year, it was replaced by the GM #351688 which continued to be used in PRODUCTION through early 1976. The GM #3878222 was discontinued from SERVICE in November, 1975 and replaced by the GM #351688 for all 64-74 applications.

The GM #351688 was discontinued from SERVICE in June, 1999.

[Loren L.]

Joe, did CA impose A.I.R. for the whole

1966 model year - or was it a requirement that commenced january 1, 1966. I seem to recall an issue with headrests seats in 1969(?) that went into effect 1/1/69 - I gues I'm wondering if the general got to use up the 64/5 bracket on early 66's????

[Joe L.]

Re: Joe, did CA impose A.I.R. for the whole

Loren-----

The requirement was imposed by the California Motor Vehicle Pollution Control Board (now known as the California Air Resources Control Board). The requirement was that all 1966 and later MODEL YEAR vehicles sold in California had to have an "approved exhaust emissions control device". However, somewhere in the law for the 1966 model year there were provisons for some "exemptions". I've never been able to "track down" just what was the basis for the "exemptions", though. However, the "manifestation" of the "exemptions" is easy to document. For 1966, these "exemptions" included the L-72 engine (installed in Corvettes and passenger cars), the L-78 engine (installed in Chevelles), and the 153 cid 4 cylinder engine (installed as the base engine in the Chevy II). Some have speculated that the exemption might have had something to do with mechanical lifters, since all of these engines were so-equipped.

However, there were other "exemptions", too. These included the 1966 Corvair with C-60 and also the 1966 Corvair with turbocharged 180 hp engine. All of these used hydraulic lifters.

Duke Williams did some research which found that there were exhaust numerical standards imposed by California for the 1966 and 1967 model years. The only thing that I was ever able to find in the law was the requirement for an "approved exhaust emissions device". However, it may be that some "arm" of the California Motor Vehicle Pollution Control Board that was charged with determining what constituted an "approved device" did set these standards in a regulatory effort.

Whatever the basis for the 1966 "exemptions", for 1967 it "went away". As far as I know, all 1967 Chevrolets delivered to California were equipped with A.I.R.

The federal requirement for exhaust emission control devices was imposed by the Department of Health and Human Services (the EPA did not exist at the time). That requirement MAY have been effective with cars built after January 1, 1968 or it may have applied to the entire 1968 model year; I'm not sure which. In any event, Chevrolet vehicles all were so-equipped from the outset of the 1968 model year whther they were actually required to be, or not.

Curiously, the definition of what constituted an "exhaust emissions control device" changed for the 1968 model year. For 1968-69 and later, many Chevrolet models equipped with automatic transmissions were NOT equipped with A.I.R. They used a system called the "controlled combustion system" (CCS). This system used modifications to the carburetor and distributor to achieve exhaust emissions control. The only exception that I know of as far as automatic-equipped Chevrolets go during this period was Corvette. ALL 1968-69 Corvettes were equipped with A.I.R, regardless of whether they had an automatic or manual transmission.

For the 1970-71 period, the use of the far cheaper CCS system greatly expanded. During this period, most Chevrolet models, including Corvette, used the CCS system. The exceptions for Corvette were LT-1 and LS-6; these used A.I.R. Why these? Well, the A.I.R. system, for all the "bad-mouthing" that's been directed at it over the years, is actually a far less performance-robbing exhaust emissions control system than the innocuous-appearing CCS system. For the most part, AIR allows an engine to be tuned for maximum performance and let's the AIR take care of exhaust emissions. The CCS system trades off some performance for exhaust emissions control. Yes, I know that the AIR-equipped 1969 300 and 350 hp small blocks were rated the same as their 1970 CCS-equipped counterparts. However, the ratings do not tell "the whole tale".