Bell Housing

[Sam D.]

cast # 3840383 what year is this this housing? Will a 10.5" pressure plate fit this housing? I have a Feb 64 built dated car. I have a 411 posi. with a 4 seed Muncie trans that matches the posi. Said in the NCRS tech guide cast # 3858403 is correct for a Feb 64. However If the production line is out of the 403 will the 3840383 have worked? Before I switch this one for a 403, I want to make sure it was not the original with the car. It looks as those it was!

Thanks,

Sam

[Joe L.]

Re: Bell Housing

cast # 3840383 what year is this this housing? Will a 10.5" pressure plate fit this housing? I have a Feb 64 built dated car. I have a 411 posi. with a 4 seed Muncie trans that matches the posi. Said in the NCRS tech guide cast # 3858403 is correct for a Feb 64. However If the production line is out of the 403 will the 3840383 have worked? Before I switch this one for a 403, I want to make sure it was not the original with the car. It looks as those it was!

Thanks,

Sam

Sam-----


The GM #3840383 was a predecessor to the 3858403. The ONLY difference between the two bellhousings involves bosses on the top of the bellhousing used for mounting the clutch cross shaft for some applications (Chevy II and maybe Camaro). That's it. The two bellhousings are 100% functionally interchangeable otherwise. For a Corvette, the bosses/tappings are completely irrelevant.

I believe that most 3840383 have NO bosses on either side, although I seem to recall at least one I saw that had an untapped boss on the driver side. The 3858403 always has a boss on the driver side and sometimes has a boss on the passenger side (used with some RH drive Chevy II's).

I have no doubt that some 3840383 bellhousings were used in PRODUCTION for some 64-67 Corvettes. I would expect their use to predominate during the 1964 model year and taper off after that.

Of course, the 3840383 bellhousing will support a 10-1/2" clutch. It's designed for use with a 12-3/4", 153 tooth flywheel and 10-1/2" clutch. This is exactly the same as the 3858403.

[Wayne M.]

Re: Bell Housing

cast # 3840383 what year is this this housing? .... Before I switch this one for a 403, I want to make sure it was not the original with the car...
Thanks,Sam

Sam -- Joe provides good info. The "orphan" 383 bellhousing keeps showing up on original cars, yet the judging manuals deny factory parentage.

My early '65 L76 (# 014xx) has a '383' which I believe is original; it has bosses on both sides, undrilled. My late '65 L78 with the '403' has bosses drilled both sides, but not tapped.

There's been threads on bellhousings before, and several 383's have been reported on the high horse cars, (but not exclusively) in '64 and '65. The '65 TIM&JG claims ALL had 403's.

The new '63-4 TIM&JG appears to have items that might give problems to the 5th ed. '65 version. Example; cooling fans. Was participating on chassis on a '64 at the recent judging school of the NCRS B.C. chapter in Vancouver. Other team members read out that the rivets attaching the blades were mushroom heads (early) and flat (late) [hope I heard correctly ]. Now this conflicts with the '65 TIM&JG which claims (typical) mushroom heads on all 3770529 blade assemblies (ie. all cars except C60 and L78). So did they start flat head rivets in latter '64 MY, then switch back to round heads in '65 ?

[Alan D.]

Re: Bell Housing

Sam,
I've owned a Mar64 FI car since Aug 67 and know past owners who never changed the bellhousing. It is a 383. Sent some GM documents before the 5th JG was written and they were accepted The 5th now states on page 137 "bell housing 3840383 was also used" So you should judge just fine! One less part to buy.

[Joe L.]

Re: Bell Housing

Sam -- Joe provides good info. The "orphan" 383 bellhousing keeps showing up on original cars, yet the judging manuals deny factory parentage.

My early '65 L76 (# 014xx) has a '383' which I believe is original; it has bosses on both sides, undrilled. My late '65 L78 with the '403' has bosses drilled both sides, but not tapped.

There's been threads on bellhousings before, and several 383's have been reported on the high horse cars, (but not exclusively) in '64 and '65. The '65 TIM&JG claims ALL had 403's.

The new '63-4 TIM&JG appears to have items that might give problems to the 5th ed. '65 version. Example; cooling fans. Was participating on chassis on a '64 at the recent judging school of the NCRS B.C. chapter in Vancouver. Other team members read out that the rivets attaching the blades were mushroom heads (early) and flat (late) [hope I heard correctly ]. Now this conflicts with the '65 TIM&JG which claims (typical) mushroom heads on all 3770529 blade assemblies (ie. all cars except C60 and L78). So did they start flat head rivets in latter '64 MY, then switch back to round heads in '65 ?

Wayne-----


The 3840383 with upper bosses on both sides is a configuration I had not seen before. That almost "completes the circle" in that it means there are 3840383 with no bosses, 1 boss, and 2 bosses and there are 3858403 with 1 boss and 2 bosses. I don't THINK that anyone will ever come up with a 3858403 with no bosses, though, but who knows?

This situation has always mystified me. Since the bosses are the only difference I've ever been able to discern between these bellhousings, I don't understand why there were 2 different casting numbers. In other words, what's the difference between a "1 boss" 3840383 and a "1 boss" 3858403? Whether, or not, the bosses are drilled and tapped should have no effect on the casting number. Of course, the finished part number for the bellhousings would be different depending on how the bosses were drilled and tapped.

As far as I can tell, there were FOUR finished part numbers for all of the above-referenced. There may have been more part numbers but these are all I can find.

GM #3840381---casting number 3840383. This was a bell housing ASSEMBLY which GM says was used for 1964 Chevrolet passenger cars and Corvette. The ASSEMBLY includes the bellhousing + the ball stud. In 1964 Chevrolet parts and other information there is no mention of the 3858403. That's because I don't even think it existed then.

In the October 1964 edition of the GM P&A Catalog (first edition including the 1965 model year) it continues to specify that the GM #3840381 (cast 3840383) as applicable to 1964 Corvettes (as well as other applications). For the first time, the GM #3858401 is included (without reference to casting number) and its applications include 1965 Corvette. These type of inclusions strongly imply that the 3840381 (cast 3840383) was used exclusively for 1964 Corvettes. As I have mentioned many times previously, this also "jives" with the fact that I just don't see the 3858403 being "around" for the 1964 model year and, certainly, not at the outset of the 64 model year. While the 3858401 (presumably of casting number 3858403) is shown for 1965 Corvettes, I think there is a very good chance, virtually proven by your cars, that it was carried over into at least the 1965 model year for certain applications. That would make sense because there was absolutely no functional reason that it could not be used for Corvettes and most other applications.

I can find no record that GM #3840383 was EVER a finished part number; it appears to be a CASTING number only.

GM #3841551---casting number 3840383. This is the finished part number for a bellhousing used for 1964-66 G-series trucks. I do not know its configuration, but it used the 3840383 casting. I suspect that the difference had something to do with the drilling and tapping of the boss(es). This bellhousing is an ASSEMBLY which includes the ball stud. However, the ball stud for the G-10 application is different than the ball stud for the Corvette and other passenger car applications. So, that MAY be entirely the reason for the difference between the 3840381 and the 3841551. There MAY be no difference, at all, with respect to the bellhousing, itself. Or, there MAY be some difference in the machining, too..

GM #3858401---shown in the October 1, 1965 edition of the P&A Catalog as casting number 3840383, but I think this is an error. The GM #3858401 is now shown as applicable to all 1964-66 Corvettes, as well as other applications. This bellhousing is an ASSEMBLY which includes the ball stud.

GM #3858401 replaces GM #3840381 for SERVICE in January, 1965. I have never seen a bellhousing with a GM #3858401 casting number, but it's possible they exist.

GM #3858403----casting number 3840383 is specified but I think this is an error. This bellhousing finished part number first appears in the October 1966 edition of the P&A Catalog as being applicable to 64-67 Corvettes as well as other applications. This bellhousing DOES NOT include a ball stud.

The GM #3858401 was discontinued from SERVICE and replaced by the GM #3858403 in June, 1966.

The GM #3841551 (G-10 van) was discontinued from SERVICE in July, 1966 and replaced by the GM #3858403.

From the 2 above references, we know that whatever features that the GM #3858401 and 3841551 had that were unique to each of them, these features were combined into the bellhousing of FINISHED PART NUMBER 3858403.

It appears that GM #3858403 was BOTH a casting number AND a finished part number. This adds to the confusion, of course.

I also determined that 1962-67 Chevy IIs DID NOT use ANY of the above bellhousings, so my hypothesis that the Chevy II application was the reason for the upper boss proves to be incorrect. It's possible, though, that the upper boss was required for the G-series truck applications. 1968+ Chevy II's used the 3858403 bellhousing. If it was these that were manufactured with right hand drive, that would explain the addition of the right side boss to the 3858403 (creating an unknown part number because these cars would have been export only). However, it would not explain the addition of the right side boss to the 3840383 as seen on one of your cars or the right side boss on any other 64-67. Perhaps there were some G-10 trucks equipped with right side steering (e.g. for export or postal vehicles) and that would explain why the right side boss appeared before 1968.

[Wayne M.]

Re: Bell Housing -- mea culpa

Wayne-----

The 3840383 with upper bosses on both sides is a configuration I had not seen before. That almost "completes the circle" in that it means there are 3840383 with no bosses, 1 boss, and 2 bosses and there are 3858403 with 1 boss and 2 bosses. I don't THINK that anyone will ever come up with a 3858403 with no bosses, though, but who knows?.....

Joe -- my appologies; I obviously didn't examine the 2 bellhousings side-by-side. I mistook the square boss near the upper bolt on the '383' for an un-drilled boss that we were discussing. Only when I took the pics of both did I realize the difference.

Here's 3 shots of the "383" on my early '65 L76 C60, and the fourth pic is of the LH side of the "403" on my 396. Latter shows the boss with what appears to be a sleeved insert (not threaded). The RH side of the bellhousing has the same (can't submit a 5th pic in a single post).

BTW, excellent research on evolution of the 383 and 403 castings and their assembly part #'s.

[Joe L.]

Re: Bell Housing -- mea culpa

Joe -- my appologies; I obviously didn't examine the 2 bellhousings side-by-side. I mistook the square boss near the upper bolt on the '383' for an un-drilled boss that we were discussing. Only when I took the pics of both did I realize the difference.

Here's 3 shots of the "383" on my early '65 L76 C60, and the fourth pic is of the LH side of the "403" on my 396. Latter shows the boss with what appears to be a sleeved insert (not threaded). The RH side of the bellhousing has the same (can't submit a 5th pic in a single post).

BTW, excellent research on evolution of the 383 and 403 castings and their assembly part #'s.

Wayne----


Yes, your '383' bellhousing is a "no boss" piece. This is the most common of the configurations of the '383'. As I mentioned, I have seen a few with the left side boss.

I don't know what the "sleeve" is in the left side boss on the '403'; I've not seen that before. Whatever it is, it's for some other application since the boss and anything connected with it is completely superfluous for the Corvette application.

It's interesting that the '403' on the big block is a "2 boss" '403'. I hypothesized that the right side boss might have been added to the '403' for 1968 or later for Chevy IIs with right hand drive, assuming that any were built. However, if your 1965 has the 2 boss configuration, then the boss was there almost from the outset of use of the '403'. I have seen '403' bellhousings, though, that had only the left side boss.

[Wayne M.]

Re: Bell Housing -- mea culpa

Wayne----
It's interesting that the '403' on the big block is a "2 boss" '403'. I hypothesized that the right side boss might have been added to the '403' for 1968 or later for Chevy IIs with right hand drive, assuming that any were built. However, if your 1965 has the 2 boss configuration, then the boss was there almost from the outset of use of the '403'. I have seen '403' bellhousings, though, that had only the left side boss.

Joe -- here's the RH pic of the '403' bellhousing on my late L78. On further examination, I now think that what I thought was an inserted sleeve (unthreaded) is actually just a recessed countersink in the native aluminum, with grime in the crevice. I inserted a pencil-type magnet into the hole and got absolutely no indication of a steel sleeve.

I find this thread very interesting -- forces me to look at my cars as never before. Notice what's left of the red/orange paint on the bellhousing. '65 Tonawanda big blocks were 100% painted, right to the transmission face.

I'd get full deduction for cleanliness, for sure .