3781021 Flywheel L79?

[Bill S.]

can any one give me an ID and specs and use of this fly wheel? ex diameter clutch size and tooth count? bill

[Louie C.]

Re: 3781021 Flywheel L79?

William, this is the standard small diameter flywheel and had a part number of 3791022 with casting number of 3791021. Are you sure yours is an "8" instead of a "9"?
My parts catalog(Sep'71) lists this flywheel for 63-68(283,327) (exc. A.T. H.D. Clutch)
Being the smaller wheel it has 153 teeth and drilled & taped for 10.5 clutch

[Bill S.]

Re: 3781021 Flywheel L79?

it is a 7. i have a clear pic on ebay. it is time to learn how to post pictures. i counted 154 but did think it was 153 i will recount. google gave one hit in reference to a 1967 L79 engine for sale having it.

[Tom P.]

Re: 3781021 Flywheel L79?

For Chevrolet V8 engines, beginning with the first 55 V8, there have ONLY been TWO sizes of flywheels/flexplates, 168 teeth and 153 teeth. I doesn't matter if the engine was a 265, 409, 350 or 502.

[Bill S.]

Re: 3781021 Flywheel L79?

thank you. thats what i am looking for. bill

[Joe L.]

Re: 3781021 Flywheel L79?

For Chevrolet V8 engines, beginning with the first 55 V8, there have ONLY been TWO sizes of flywheels/flexplates, 168 teeth and 153 teeth. I doesn't matter if the engine was a 265, 409, 350 or 502.

Tom------


Yup. And for some unknown reason, GM seemed to "alternate" on the use of the two sizes between generations of Corvettes. To wit:

C1----All 14", 168 tooth

C2----Mostly 12-3/4", 153 tooth (except 66-67 with L-36, L-72, L-68 and L-71)

C3----Mostly 14", 168 tooth (except 68 small block, all L-88, and ZR-1)

C4----All 12-3/4", 153 tooth

C5/C6----All 14", 168 tooth

[Tom P.]

Re: 3781021 Flywheel L79?

Joe,
Even though BB engines, EXCEPT the 65 396, got the big 168 teeth flywheel, didn't they get the smaller 153 teeth flywheel if the car came with the HD dual disc clutch (such as on an L88)?

[Joe L.]

Re: 3781021 Flywheel L79?

Joe,
Even though BB engines, EXCEPT the 65 396, got the big 168 teeth flywheel, didn't they get the smaller 153 teeth flywheel if the car came with the HD dual disc clutch (such as on an L88)?

Tom-----

All L-88 (and ZL-1) with manual transmission used a 12-3/4", 153 tooth flywheel. No PRODUCTION L-88 ever used a dual disc clutch although that seems to be a pretty widely held belief. The only applications that ever used the dual disc clutch were as follows:

1969 with L-71 and MA-6 HD clutch option

1971 all LS-6 with 4 speed

The dual disc clutch used a special 14", 168 tooth flywheel, although it used 10" friction discs.

[Tom P.]

Re: 3781021 Flywheel L79?

Joe,
I could cut off 3 fingers from one hand and count all the GENUINE L88 cars that I've seen in person on that one hand. But, I never crawled under them to check the size of the bell housing (which would indicate flywheel size).
Also, I've always understood that the HD dual disc clutch was a 10in clutch, but I've never actually had one in my hands. Soooooooooooo, if the dual disc clutch was mounted on a 14in flywheel, did it use the same bolt pattern as a 10.4 pressure plate, or an 11in pressure plate?
Furthermore, if the L88s and ZL1s only used a 153 teeth flywheel (I'm guessing the lightweight version), then that means they could have ONLY had the 10.4 clutch. Right?

[Wayne M.]

Re: 3781021 Flywheel L79?

Next best thing to having one in your hands -- a pic.

This is from "How to hotrod BB Chevs" 1971.

There's also a Chev profile design drawing of the complete flywheel, disc plates, cover, T.O. bearing and fork, and bellhousing in the "1969 New Product Training Program Booklet".

[Joe L.]

Re: 3781021 Flywheel L79?

Joe,
I could cut off 3 fingers from one hand and count all the GENUINE L88 cars that I've seen in person on that one hand. But, I never crawled under them to check the size of the bell housing (which would indicate flywheel size).
Also, I've always understood that the HD dual disc clutch was a 10in clutch, but I've never actually had one in my hands. Soooooooooooo, if the dual disc clutch was mounted on a 14in flywheel, did it use the same bolt pattern as a 10.4 pressure plate, or an 11in pressure plate?
Furthermore, if the L88s and ZL1s only used a 153 teeth flywheel (I'm guessing the lightweight version), then that means they could have ONLY had the 10.4 clutch. Right?

Tom-----


If you find any bellhousing on an original L-88 Corvette that's not a GM #3858403 (or, POSSIBLY, a GM #3840383), then it's not the one that was originally installed on the car. All L-88 and ZL-1 with manual transmission used a lightweight 12-3/4" flywheel, GM #3866735, and 10.4" clutch. However, not all L-88 and ZL-1 were equipped with a manual transmission. All 1967-68 were but for 1969, some L-88 and ZL-1 were equipped with a special THM-400. Those applications used a 14", 168 tooth flexplate.

The 10.4" clutch used for L-88 and ZL-1 was not the same as that used for 63-68 small blocks. L-88 and ZL-1 used a HD pressure plate and disc of GM #3886066 and GM #3886059, respectively. While the L-88 and ZL-1 flywheel was also used for 1965 L-78, the same pressure plate and disc were not used for 1965 L-78. The only other applications for the pressure plate was 1970-72 ZR-1 and the only other application for the disc was 1970 ZR-1 (although 71-72 ZR-1 used a similar disc but with 26 splines).

The dual disc clutch used a special 14", 168 tooth flywheel that was drilled for the special size of the 10" dual disc pressure plate and cover assembly. This flywheel was not used for any other application except 1969 with MA-6 and all 1971 with LS-6 and manual transmission. 1969 with MA-6 is the same as all 1971 LS-6 with manual transmission EXCEPT the dual discs use 26 splines rather than the 10 used for 1969 MA-6.