Flywheel Differences

[Joe C.]

What, if anything, is the diff between 3791022 and 3973452. The first was originally used with the "419" bellhousing, and the latter was used with the "403".
Thanks in advance.

Joe

[Joe L.]

Re: Flywheel Differences

What, if anything, is the diff between 3791022 and 3973452. The first was originally used with the "419" bellhousing, and the latter was used with the "403".
Thanks in advance.

Joe

Joe-----


I can't with 100% confidence answer your question. However, I can tell you this:

First, the information in your second sentence is partially incorrect. The GM #3791022 flywheel, casting number 3791021, was used with the 1963-only GM #3788419 bellhousing, cast GM #3788421. However, the exact same flywheel was also used with the GM #3840383 and GM #3858403 bellhousings. The GM #3791022 flywheel was used for ALL 1963-68 Corvette small blocks. It is a standard weight, 12-3/4" flywheel with 153 tooth ring gear designed for use with 10-1/2" clutches.

Sometime in late 1969, a new flywheel was released of similar configuration. It was GM #3973452. I do not know, for sure, if it was based on the 3791021 casting, as some GM references indicate, or if it was a new casting. However, I think it was a new casting of unknown-to-me casting number but likely 397345?. This new flywheel, as far as Corvettes go, was SERVICE-only piece, but it may have been used for other Chevrolet applications in PRODUCTION. The GM #3973452 replaced the GM #3791022 for SERVICE in December, 1971. However, the fact that it was released in late 1969 indicates that it had other applications, most likely truck.

No Corvette small block after 1968 and before 1984 used a 12-3/4" flywheel EXCEPT 70-72 ZR-1. However, these used a lightweight flywheel of GM #3866735 (1970) and GM #3991406 (71-72).

In any event, the GM #3791022 and GM #3973452 are 100% FUNCTIONALLY EQUIVALENT AND INTERCHANGEABLE. My GUESS is that the difference involved some difference in the configuration of the casting, probably to improve strength or expand compatibilities for its use for other applications.

The GM #3973452 was discontinued from SERVICE in June, 1977 and replaced by GM #366860. How it differed, I do not know. The GM #366860 was discontinued about 5 years ago without supercession.

[Timothy B.]

Re: Flywheel Differences

Joe,

Could this have been the service flywheel you are talking about. This came with my 63 and it weighs approx the same as the 3791021. The casting # (3973455 N) I have never been able to identify but others here in the past have posted this # with questions.

[Joe C.]

Re: Flywheel Differences

Joe-----


I can't with 100% confidence answer your question. However, I can tell you this:

First, the information in your second sentence is partially incorrect. The GM #3791022 flywheel, casting number 3791021, was used with the 1963-only GM #3788419 bellhousing, cast GM #3788421. However, the exact same flywheel was also used with the GM #3840383 and GM #3858403 bellhousings. The GM #3791022 flywheel was used for ALL 1963-68 Corvette small blocks. It is a standard weight, 12-3/4" flywheel with 153 tooth ring gear designed for use with 10-1/2" clutches.

Sometime in late 1969, a new flywheel was released of similar configuration. It was GM #3973452. I do not know, for sure, if it was based on the 3791021 casting, as some GM references indicate, or if it was a new casting. However, I think it was a new casting of unknown-to-me casting number but likely 397345?. This new flywheel, as far as Corvettes go, was SERVICE-only piece, but it may have been used for other Chevrolet applications in PRODUCTION. The GM #3973452 replaced the GM #3791022 for SERVICE in December, 1971. However, the fact that it was released in late 1969 indicates that it had other applications, most likely truck.

No Corvette small block after 1968 and before 1984 used a 12-3/4" flywheel EXCEPT 70-72 ZR-1. However, these used a lightweight flywheel of GM #3866735 (1970) and GM #3991406 (71-72).

In any event, the GM #3791022 and GM #3973452 are 100% FUNCTIONALLY EQUIVALENT AND INTERCHANGEABLE. My GUESS is that the difference involved some difference in the configuration of the casting, probably to improve strength or expand compatibilities for its use for other applications.

The GM #3973452 was discontinued from SERVICE in June, 1977 and replaced by GM #366860. How it differed, I do not know. The GM #366860 was discontinued about 5 years ago without supercession.

Thanks Joe........the 2 underlined sentences above, are very helpful.
I currently have a "022" unit installed on my 1965 L76. I was lucky, and bought it NIB at Carlisle a few years ago, at a bargain price. I am now going to replace it with this, because it will be regularly subject to "off-road" duty:

http://store.summitracing.com/partdetail.asp?part=RAM%2D1510&autoview=sku

Here is what I had found previously, regarding the flywheel:

Chevrolet Passenger Car flywheels
265-350cid V-8, Manual Transmission

GM Part No. Identification No. Year Model

3739423 w/10" coil & diaphragm spring clutch
55 8-cyl exc. H D clutch 4-bbl


(11 5/8" bolt circle) cast 3829004
56Pass. w/2-bbl (exc. H D clutch)
56 Pass. w/4 bbl.
56-58Pass. (283 exc. H D clutch dual 4-bbl F. I
w/4-spd)
59-61Pass. (283 exc. o/d)
62Pass. (8-cyl)

3998281w/11" coil spring clutch (12 5/8" bolt
circle) solid type
55-56Pass. w/CAC (8 cyl)
55-56Pass. w/4-bbl
57Pass. (exc. 4-bbl, dual 4-bbl)
58Pass. w/H D clutch (283 exc. 4-bbl, F.I. o/d)
58-61Pass. w/o/d (283)
66-68Pass. w/H D clutch (327)
67-69Chevelle w/H D clutch (327)
67Chevelle w/H D clutch (283)
67-69Camaro, Chevy (350)
69Pass. (350)
70All w/4-bbl (350)
70-74All w/Sp H Per. (350)

3791022 solid type (cast 3791021)
63-64Pass. (283, 327 exc. H D clutch)

3973452 solid type, as above
64-67 All (283 exc. H D clutch)
66-67Pass. w/H D clutch (283)
64-68All (327 exc. H D clutch)
67-69All (302)
69 Pass. w/reg. fuel (327, 350)

3986390
70-72All w/2-bbl. (350)
71Chevelle w/4-bbl (350 exc. Monte Carlo)
73-74All (350 exc. Sp H/Per.)
75Nova, Camaro (350)

[Joe L.]

Re: Flywheel Differences

Joe,

Could this have been the service flywheel you are talking about. This came with my 63 and it weighs approx the same as the 3791021. The casting # (3973455 N) I have never been able to identify but others here in the past have posted this # with questions.

Tim-----


Yes, I'm virtually certain now that's the casting used for the GM PART #3973452 flywheel. Thanks for posting the photos. Could you also post a photo of the complete reverse side of the flywheel if it's not already installed in the car? Also, what is the actual weight of it?

[Timothy B.]

Re: Flywheel Differences

Joe,

I will post photos of this flywheel tomorrow because it's at my shop in the glassbead cabinet and I can't get to it today. I remember the date is consistent with your info about the years this flywheel was available. I also remember weighing the 3791021 flywheel and the 3973455 flywheel and they were both approx 29-30 lbs. but I will double check. I am not sure why the "N" in the part #.

[Joe C.]

Re: Flywheel Differences

Joe and Tim,

Iffen you all want any pictures/vital info on the 3791021/22 flywheel for comparison, let me know. Mine is cast L 12 7 (12/12/67); has "N" stamp (NOT cast) which MIGHT also indicate "noodle-ular". But, you have to wait a few days until I get my $E%^&^* Canon digital back from warranty repairs.

Joe

[Timothy B.]

Re: Flywheel Differences

Joe,


Pictures would be nice and I will provide pictures of the 3973455N on the back side and front to compare.

[Joe L.]

Re: Flywheel Differences

Joe,

I will post photos of this flywheel tomorrow because it's at my shop in the glassbead cabinet and I can't get to it today. I remember the date is consistent with your info about the years this flywheel was available. I also remember weighing the 3791021 flywheel and the 3973455 flywheel and they were both approx 29-30 lbs. but I will double check. I am not sure why the "N" in the part #.

Tim-----

I look forward to the pictures. The "N" suffix for the casting number indicates nodular iron. Sometimes, one will see an "NF" suffix on cast parts. This denotes "nodular ferrous". I don't know how or if nodular iron and "nodular ferris" differ. "Ferrous" to me is synonymous with "iron".

[Joe L.]

Re: Flywheel Differences

Joe and Tim,

Iffen you all want any pictures/vital info on the 3791021/22 flywheel for comparison, let me know. Mine is cast L 12 7 (12/12/67); has "N" stamp (NOT cast) which MIGHT also indicate "noodle-ular". But, you have to wait a few days until I get my $E%^&^* Canon digital back from warranty repairs.

Joe

Joe


Yes, I'd definitely like to see photos when you get your camera going again.

I've never seen a 3791021 flywheel with a STAMPED "N" suffix. However, it's quite interesting. What it may imply is that the casting was originally of gray iron. At some point, that may have changed to nodular iron. Before the casting number had the "N" added to the pattern, they may have just stamped them with the "N" to denote the new material. That's just a guess, though.

[Timothy B.]

Re: Flywheel Differences

Joe and Joe,

Here are the pictures of the 3973455N flywheel, I have also included a picture of the 3791021 for comparision. It's not a good picture but it's the only one I have. When Joe posts his pictures we can see the difference if any.

[Joe C.]

Re: Flywheel Differences

No camera yet....but I'll have mine back either Saturday or Monday.

Mine looks identical, except for the casting number. Mine also has a casting clock on the non-friction side.

[Joe C.]

3791021/22 Flywheel

Here are the pictures of my 3791021/22 flywheel. I have some closeup shots, if anyone would like. Notice the stamped-in "F", "N", and "1". To me, it looks identical to Timothy's 3973455 N. Weight is 30 lbs.

[Timothy B.]

Re: Flywheel Differences

Joe,

I can't tell the difference from either flywheel. I will look close at mine for stamped #'s around the perimeter. I recall mine weighted 29 lbs. as it's been turned in the past. I am glad to know about the #3973455 flywheel because I never had any luck finding info with the cast #. Thanks for the pictures.