do the 421 & 383 1964 bellhousings have the same size opening on transmission side?

[Geoff B.]

I am restoring a 1964 L76. I have replaced the clutch & flywheel and tracked down bellhousing 3788421. I did have bellhousing 3872444 installed, which I think is correct for 65 or 66. When I went to bolt the engine and tranny together, I noticed the opening on the 3788421 bellhousing does not fit over the housing and bolts that hold the tranny shaft.

I'm wondering if the 3840383 bellhousing has a larger opening.

The tranny is a muncie 4 speed. If the bellhousings have the same size opening, is it possible the tranny is from a later year and had a larger housing around the shaft?

Thanks in advance for any help. I'm hoping there is a solution that does not include tracking down a 1964 muncie 4-speed to replace the one I have.

[Tom D.]

Re: do the 421 & 383 1964 bellhousings have the same size opening on transmission sid

https://www.forums.ncrs.org/showthre...ht=bellhousing
See above, and related discussions.

421 is for 63 only. 444 might be the (hard to find) big block large flywheel version. Others are looking for that 421 version...

[Joe L.]

Re: do the 421 & 383 1964 bellhousings have the same size opening on transmission sid

I am restoring a 1964 L76. I have replaced the clutch & flywheel and tracked down bellhousing 3788421. I did have bellhousing 3872444 installed, which I think is correct for 65 or 66. When I went to bolt the engine and tranny together, I noticed the opening on the 3788421 bellhousing does not fit over the housing and bolts that hold the tranny shaft.

I'm wondering if the 3840383 bellhousing has a larger opening.

The tranny is a muncie 4 speed. If the bellhousings have the same size opening, is it possible the tranny is from a later year and had a larger housing around the shaft?

Thanks in advance for any help. I'm hoping there is a solution that does not include tracking down a 1964 muncie 4-speed to replace the one I have.

Geoff-----


The GM #3788421 bellhousing was used for 1963 only and has a smaller transmission front bearing retainer orifice than any other Corvette bellhousing. The 3788421 is designed for use with a 12-3/4" flywheel. The 3840383 and 3858403 are also designed for use with a 12-3/4" flywheel.

The GM #3872444 was used on Corvettes for 1966 and early 1967. It is designed for use with a 14" flywheel and since that size flywheel for 1966 and 1967 was used only for most big blocks, the 3872444 was used only for big blocks. However, it can be used for small blocks with 14" flywheel. It has the same size front bearing retainer orifice as the 3840383 and the 3858403. The GM #3899621 which was used for most 1968-81 Corvette applications is identical with the 3872444 with respect to all dimensions and differs only with respect to relatively minor casting configuration.

[Tom P.]

Re: do the 421 & 383 1964 bellhousings have the same size opening on transmission sid

Geoff,
Joe is correct in all respects regarding the 421, 383, 403, 444, 621 housings. The ONLY thing I might add is that the 444 housing (used with the larger 14in diameter, 168 teeth flywheels) was also used on 66/early 67 Chevelles with a big block. My point is that the 444 is not unique to the Corvette. Although, the 444 is somewhat difficult to find as well as somewhat pricy, it might be easier to locate in the Chevelle community.
For the 63-65 Vettes, there were no engines that used the large 168 teeth flywheel, thus no large bell housing was used in those years. The 66 model was the first year to go back to a large flywheel/bell housing-------------------which I have NEVER understood. The pass cars (as well as trucks) ALWAYS were available with the big flywheel. Although, a big bell housing for the 64-65 cars is really rare and somewhat unique.

[David L.]

Re: do the 421 & 383 1964 bellhousings have the same size opening on transmission sid

Over the last 32 years I have had all of theses bellhousings (421, 383, 403, 444, and 621). The 421 bellhousing has a 4 3/16" dia. hole while the rest of them have a 4 11/16" hole.

My 1966 Corvette (Feb. 1966) w/original Muncie but replacement engine (purchased in 1979) came with a bellhousing with "GM", "3858403" and "1" castings. I believe it is original but I am not 100% sure. Back in the early 1980's a neighbor of mine had a matching numbers 1966 Corvette w/327 & Muncie with a 3858403 bellhousing.

I also have in my "collection" a bellhousing with "7" and "3858403" castings but without the "GM" casting.

I believe (but I may be wrong) that the 1964 Corvettes were issued the 3840383 bellhousing. I once owned a 3840383 bellhousing that came with a rubber boot with "3820875" molded into the rubber. According to my research the 3820875 rubber boot was used on 1963 and early 1964 Chevrolet models. The late 1964-1967 models used a 3844208 rubber boot. I have compared the 3840383 bellhousing with the 3858403 bellhousing and could not really find any differences except for the casting numbers.

My 1964 Chevrolet Parts Catalog lists GM # 3840381 as the part number for the bellhousing for 64 Chev. Pass. & Corvette (283,327). My 1965 Chevrolet Parts Catalog (Oct 1964) lists GM # 3840381 as the part number for 64 Chev. Pass. & Corvette (283,327) and is described as "HOUSING ASSY., clutch (Ident. 3840383)" and lists GM # 3858401 as the part number for 65 Chev. Pass. & Corvette with a description of "HOUSING ASSY., clutch". According to Chevrolet Parts History GM # 3858401 was transferred to GM # 3858403 in June 1966.

The 3899621 bellhousing is also original equipment on the 1970 Camaro SS350 w/Muncie and a 14" flywheel.

Bellhousings that were made before 1973 have the "GM" casting on the side while bellhousings made 1973-1974 have the "GM" casting on the top.

Dave

[Geoff B.]

Re: do the 421 & 383 1964 bellhousings have the same size opening on transmission sid

Thanks for the information. I should have done more research ahead of time. My judging guide just says the 421 was used throughout 63 and 64, so I assumed they were all interchangeable. I'll track down a 383 since it sounds like that has a larger opening on the tranny side and that should solve the problem.

[David L.]

Re: do the 421 & 383 1964 bellhousings have the same size opening on transmission sid

Geoff,

I do not have any judging guides and would would never use them. I rely on 32 years of research, 55 or more vintage Chevrolet parts catalog, assembly manuals, and conversing with other Corvette & Camaro restorers with many years of experience and who are dedicated to using factory original parts.

Most 1963 Corvettes were issued the T10 4-speed while "late" 1963 Corvettes used a Muncie with a casting number 3831704 on the main case.

The 1964 and 1965 Corvettes used a Muncie with a casting number of 3851325 on the main case which will not fit a 3788421 bellhousings.

What good are the judging guides if they are wrong?

Dave

[Tom P.]

Re: do the 421 & 383 1964 bellhousings have the same size opening on transmission sid

Only 32yrs?????????????????????

[Joe L.]

Re: do the 421 & 383 1964 bellhousings have the same size opening on transmission sid

Geoff,
Joe is correct in all respects regarding the 421, 383, 403, 444, 621 housings. The ONLY thing I might add is that the 444 housing (used with the larger 14in diameter, 168 teeth flywheels) was also used on 66/early 67 Chevelles with a big block. My point is that the 444 is not unique to the Corvette. Although, the 444 is somewhat difficult to find as well as somewhat pricy, it might be easier to locate in the Chevelle community.
For the 63-65 Vettes, there were no engines that used the large 168 teeth flywheel, thus no large bell housing was used in those years. The 66 model was the first year to go back to a large flywheel/bell housing-------------------which I have NEVER understood. The pass cars (as well as trucks) ALWAYS were available with the big flywheel. Although, a big bell housing for the 64-65 cars is really rare and somewhat unique.

Tom------

All C1 Corvette= 14" flywheels

Most C2 Corvette= 12-3/4" flywheels (except 66-67 L-36, L-68, L-71, L-72)

Most C3 Corvette= 14" flywheels (except 1968 small block, L-88, ZL-1, and 1970-72 ZR-1)

All C4 Corvette= 12-3/4" flywheels

All C5 Corvette= 14" flywheels

Apparently, GM wanted to "rotate" the flywheel size for each generation Corvette. I believe that C6 remained the same as C5, though.

[David L.]

Re: do the 421 & 383 1964 bellhousings have the same size opening on transmission sid

Only 32yrs?????????????????????

Yes, only 32 years. I guess that I am still a "Corvette rookie" by some standards but I did my first engine swap (1959 Chev. 6 cyl., A.T. to a 283 w/3-speed M.T. & Hurst Mystery shifter) when I was 18 in the summer of 1965 so actually I have been involved with Chevrolets for almost 47 years.