64 Bellhousing

[Gary D.]

Can anyone tell me what bellhousing # 3840383 fits? I just cleaned it up and the 63/64 JG call for a different #. This car is very original and I do not believe someone changed it. Thanks to all Gary

[Joe L.]

Re: 64 Bellhousing

Gary-----

I believe that the GM #3840383 was originally used on many, if not all, 1964 Corvettes (as well as certain other Chevrolet models, too). While the GM #3858403 is generally considered the "correct" bellhousing for 1964, if it was used at all for 1964, it was used alternately with the 3840383.

The only difference between these bellhousings described above is the presence or absence of a boss on the upper side(s) of the bellhousing. The 3840383 generally has no bosses (although I've seen a few which DO have a boss on the upper, left side which is not drilled and tapped). The GM #3858403 always has a drilled and tapped boss on the upper left side and some have a boss, sometimes drilled and tapped, on the upper right side.

The bosses are used as an anchor point for the clutch cross shaft for some applications. However, they are not used for ANY Corvette application. So, they are completely superfluous for Corvettes.

By the way, the GM #3840383 bellhousing (actually, that was the casting number; the PART number was GM #3840381) was discontinued in January, 1965 and replaced by the 3858401 (the FIRST PART number for the 3858403 casting). So, after this time, anyone purchasing a bellhousing for any 64 Corvette would have received the GM #3858403. 41 years is a lot of time for Corvettes to possibly require a bellhousing replacement (for things like a cracked bellhousing from road debris damage, having installed a scattershield for drag strip requirements, not saving the original, and wanting to go back to a stock bellhousing, etc.). I think this "route" is how the 3858403 bellhousing has come to be considered correct for 1964 Corvettes. As I say, though, it's possible that the 3858403 was used originally on SOME 1964 Corvettes. I consider it CERTAIN that it was not used on ALL 1964 Corvettes.

[Alan Drake]

Re: 64 Bellhousing

Hi Joe,
Seems as if you have looked at this problem before - say for me!

Gary, since I had the same problem on my 64, Joe also mentioned that the survey in Noland Adams book, page 249, also showed 64's with the 383 bellhousing. I have been gathering some info on the subject to show a judge if the question arises. Still trying to get a copy of the page from P&A Catalog Oct 1, 1963 & 64 that shows the 383 for the 64.

Joe, hope you have a file on the subject so it can be pasted as an answer. Thanks for your past help here.
Alan

[Wayne M.]

383 vs. 403

Alan -- quite an interesting topic; the SERVICE documentation (sometimes questionable accuracy) is available, but what the factory did is what counts for NCRS.

I don't have an Oct '64 Chassis P&A30, but I do have the Oct '64 Parts History Index (found at the back of the Body P&A30), and it shows nothing for 3840383 (or 01), which usually means that as of this date, they had not started using 3858403 (or 01) for SERVICE.

The next oldest catalog I have is a July 1 1965 Revision; Parts History says nothing about 3840383/01; the Chassis P&A30 Gr 0.683 shows: '64-65 Passenger (283,327), also '64-65 Corvette (327, 396), and '64-65 Taxi (230) as using part # 3858401, but with ident. # 3840383 !! Does this mean they were using up the 383's in service ? Also, same catalog, '64-65 G-10 (exc. 194) calls for bellhousing part # 3841551, again with ident No. 3840383 -- does this maybe mean the 383 was drilled / taped differently for this truck application ?

For the first time, in the P&A30 of Oct 1, 1965, the history shows as Joe has given [3840383/01 discontinued in Jan '65; replaced by 3858403/01]. -- but remember this is the first SERVICE replacement entry.

Now jump forward to Jan 1 1970 (I'm too lazy to check the '67, '68, '69 catalogs); P&A30B (Corvette only catalog) It shows '64-68 Corvette (327, 396), 66 Corvette w/Sp. H.Per (427), and [the L-88 / ZL1s] '67-69 Corvette w/H.D., AL. Cyl. and Case (427) as all using # 3858403 (they've dropped calling it by the 01 part number), BUT IT STILL CARRIES IDENT No. 3840383 -- go figure.

Good luck in convincing the judges on this one. I'm in the same boat with my early '65 L76, (014xx) which also has the "383".

[Joe L.]

Re: 383 vs. 403

Wayne-----

I have found the SERVICE parts records to be remarkably accurate with respect to the parts used in PRODUCTION. They are not 100% accurate, of course, since no documentation of any kind falls into that category. Even the AIM's are not 100% accurate relative to what parts were used in PRODUCTION.

In many, many cases I have cross-checked SERVICE parts information against multiple other sources and, virtually always, it checks out. Quite frankly, I am constantly amazed at just how accurate it is. However, it really should not be all that surprising since the application and part number information in SERVICE parts catalogs is sourced from PRODUCTION data; it's not just something that GMSPO comes up with on their own. There are, of course, cases in which, for a variety of reasons, a SERVICE part number may be different than a PRODUCTION part number. Even then, though, it's often the same part(s) supplied in a different way (i.e. instructions included, hardware included, etc., etc.).

Also, keep in mind that SERVICE parts catalogs were generally updated 3-4 times per model year. This was to keep up with PRODUCTION part number changes.

The most accurate SERVICE parts catalogs for any particular car will be those published within a short time after the assembly of that car. After that, catalogs may reflect supercessions, consolidations, etc. Although this usually represents a very small number of parts from, say, one edition to the next, it needs to be considered.

As far as the 3840383 bellhousing goes, this was a bellhousing that was manufactured for only about one model year, that model year being 1964. There's absolutely no reason to believe that it would have been used for other Chevrolet applications for the 1964 model year while the 3858403 was used for Corvette. As I've mentioned, Corvette did not require the additional feature of the '403' bellhousing (nor did any other 1964 Chevrolet model that I'm aware of). So, if the 3840383 bellhousing was not used during the 1964 model year, then where did the '383' bellhousings that are out there come from? It's very unlikely that the '383' bellhousing would ever have been used as a SERVICE-only replacement. That's because it lacked features necessary for some 1965+ applications. MUCH more likely is that any stock of '383' bellhousings that existed would have been used in PRODUCTION where GM could ensure that they were used only for applications not requiring the upper boss(s). In fact, that may well be how the '383' ended up on 1965 Corvettes, including yours.

Another item of note here is the fact that the 3858403 part number seems "out-of-sequence" for a 1964 application and, especially, any earlier 1964 application. While I'll be the first one to say that inferring part release dates by part number sequence is not, by any means, an "exact science" (I've said that many times before here), it is ONE of the "tools" that we can very often reliably use to infer the release period of a part. 3858403 looks to me like too late of a part number to have been around, at least at the start of the 1964 model year. That doesn't mean that it wasn't, though.

As far as the reference in the P&A Catalogs is concerned that the 3858401 or 3858403 used the 3840383 casting number, I do believe that's an error in the P&A Catalogs. I have found that VERY often, the parenthetical information on the part description line is inaccurate. That's because, while the information on the left side of the catalog lines is more-or-less assiduously updated, the parenthetical information on the right side is not. VERY often, the parenthetical information represents an anachronism. I never rely on it without cross checking.

Given what I know about the '383' and '403' bellhousings what I THINK happened is this: all 1963+ Corvette (and most other Chevrolet) bellhousings were a die casting manufactured from permanent molds. Very likely, the molds used for the '383' casting were manufactured by modifying the molds used for the earlier, 63-only '421' casting. During the 1964 model year, with the apparent future need for a casting with the upper left boss, the '383' molds were modified. However, given the wide use of these bellhousings, there must have been a LOT of molds. So, they couldn't all be modified at the same time. Once modified, the boss was added and the casting number was changed. For some period of time, BOTH bellhousings were being manufactured. It didn't matter for the 1964 model year which one was installed for any engine requiring this configuration bellhousing---the boss was superfluous for 1964 models. If there were any '383' bellhousings being produced or in inventory at the end of the 1964 model years, they could be used in PRODUCTION for any 1965 applications not requiring the boss (which was most 1965 applications, including Corvette).

Also, I think that you are mistaken about the Parts History index published July 1, 1965 not referring, at all, to the 3840383 or 3840381. If you're not mistaken, then you have a different page dated July 1, 1965 than I have. My page dated July 1, 1965 shows the GM #3840381 (the part number for one of the bellhousings manufactured from the 3840383 casting and the one used for Corvettes)to have been discontinued in January, 1965 and replaced by the GM #3858401 at that time.

Notwithstanding all of the above and as I've said many times before, empirical information is always the best. In other words, what was actually used is best determined by observation of original cars. The problem is that how does one know that any car today, represented as "original" is ACTUALLY original, especially with respect to a feature like this bellhousing? Unless someone has owned a car since day-one and can attest to the fact that a certain component has never been changed, how can anyone be sure? Even then, all that says is that's how THAT car was built and not necessarily how EVERY car was built.

Furthermore, with respect to these bellhousings, there are several other "factors" which render assessments of originality "uncertain". First, as I've mentioned before, is the fact that the 3840383 bellhousing was discontinued more than 42 years ago. So, any 1964 Corvette requiring a replacement after that time would definitely have been supplied a GM #3858403. 42 years is a long time "for things to have happened to any car".

Secondly, the 3858403 bellhousing is WAY more common than the 3840383. The '403' bellhousing was manufactured for about 25 years and used on a wide array of applications. They are almost a "dime-a-dozen" today (often sell on eBay for 50 bucks or less and many times receive no bids, at all). VERY, VERY easy to find at swap meets, too, and one is always in a great negotiating position since there are so many to negotiate over (and, the sellers know that). So, there are lots of used ones out there that could have "found their way onto" a 1964 Corvette over the course of 42 years. In fact, I'd say that the chances that a '383' bellhousing could have POST-PRODUCTION "found its way onto" a 1964 (or, 1965) Corvette is FAR, FAR less than a '403' "finding its way onto" such a car.

Thirdly, as I understand it, the 3858403 is considered the only correct bellhousing for 1964 Corvettes. I'm not sure if that's the case, but I thought I had heard that. If so, how many 1964's may have had their '383' bellhousings REMOVED and REPLACED by the '403' in order to make the car "correct"? Especially since the "correct" '403' bellhousing is so easy to find!

[Joe L.]

P&A Catalog Page #1

Here's a scan of a relevant page from the October, 1963 Catalog

[Joe L.]

P&A Catalog Page #2

Here's a scan of the relevant catalog page from October 1, 1964. This is the most interesting of the 3 that I will post. Note that as of this time, one could order a GM #3840381 for a 1964 Corvette OR a GM #3858401 for a 1965 Corvette.

[Joe L.]

P&A Catalog Page #3

Here's the final one, which I think is the same page you referred to. This is after the 3840381 was discontinued and replaced by the 3858401.

By the way, this is the first appearance of the parenthetical anachronism calling for the 3840383 casting number for the 3858401 bellhousing. I believe that this reference was "carried over" from the 1964 listing and is now inaccurate. If it's not, then 1965 Corvettes (and, all others using the 3858401 or 3858403 PART NUMBER bellhousings) should really have the 3840383 casting number upon them. The 3840383 casting number was shown parenthetically for the 3858401 and 3858403 bellhousings right up until the time that the 3858403 was discontinued from SERVICE in February, 1991.

Also, there was, of course, never a bellhousing with a casting number of 3858401. That was a PART NUMBER for one of the bellhousings manufactured from the 3858403 casting. The GM PART #3858401 was discontinued in June, 1966 and replaced by GM PART #3858403. So, as of that date, the part number and the casting number were the same. I see 2 possible reasons that this happened:

1) It was just a part number change to avoid the confusion created by the prior difference in the casting versus part numbers. Supporting that is the fact that when the part number changed, the instructions to Chevrolet dealers with respect to the 3858401 and 3858403 was "mix and sell". That USUALLY means that the 3858401 and 3858403 had to be functionally identical in every way. One could not have had any feature that the other one didn't have or it would not be possible to use it for the application requiring the missing feature;

2) There was some actual change in the the FINISHED part from the GM PART #3858401 to the GM PART #3858403, even though the same casting was used for both. As I mentioned before, I'm quite sure that there were changes in the part and, even, the casting. I've seen some '403' bellhousings with only a left side upper boss which was drilled and tapped, some that had bosses on both the left and right upper sides with only the left one drilled and tapped, and some that had both bosses drilled and tapped.

[Joe L.]

Re: 64 Bellhousing

Alan-----

No, I'm not really maintaining any file on this subject. I do maintain files on some issues that are of "primary interest" to me. This is not one of them, though. So, you'll have to maintain your own file from what I post and from what ends up in the archives. I depend on the archives for "maintaining files" for issues like this that are of "secondary interest" to me.

[Wayne M.]

Thanks, Joe -- this should help Gary and Alan ...

... with respect to service documentation.

You are correct; your page #3 is what I was referring to in my catalogs. I should correct my statement about the '65 P&A30 History -- it was Oct 1 1964 original issue (as you mention) and NOT the July '65 Rev; I just assumed since my Chassis book was the later version, the Body catalog also was (not !).

I'd take a few pictures to show everyone what we're talking about with "boss / no boss" and "drilled", but it's too cold in the garage . Wish I knew how to collate individual jpegs into a single image (ie. side by side, for the best comparison).