What Flywheel is this?

[Joe S.]

I've got a friends 63 here that the clutch was almost gone in. I pull it apart today and the flywheel is nothing like my 63 (I thought they were all the same). It's very light and almost shaped like a pie tin. It has what appears to be #3858579 or 3856579 on it. There is currently a 10" disc in it but it looks like a 10.5" will just make it (if surfaced to get the lip off).

I had already ordered a new 10.5" clutch kit for it and was going to have the thing surfaced and balanced. Any idea what this puppy is?

Thanks

[Joe L.]

Re: What Flywheel is this?

Joe------

Easy one. The GM casting #3856579 is a 12-3/4", 153 tooth, lightweight (~16 lb) flywheel. It was originally known as GM PART #3866735.

In PRODUCTION, this flywheel was used for the following applications:

1965---L-78
1967-69---L-88/ZL-1
1970-72---ZR-1

It's a very popular retrofit flywheel, though, for folks that want a lightweight flywheel (I'm not one of them). It will fit any internally balanced, 2 piece rear seal big block or small block. It's still available under GM PART #14085720.

[Joe S.]

Re: What Flywheel is this?

Joe, how do you sleep at night ;-)

Thanks much.

[Mark S. Lovejoy]

Joe;

Would you use this flywheel if you were to build a L-78? Is there a better alternative?

Thanks,

Mark

[Joe L.]

Re: Joe;

Mark------

If I were building an L-78 (or, an original configuration L-88/ZL-1), I would use this flywheel. No doubt about it. If I were building just about anything else for a STREET application, I wouldn't use it. For my "ZL-1" project, I could have gone either way---the original 12-3/4" flywheel/10-1/2" clutch or the 14" flywheel/11" clutch. I have all the NOS components for either set-up , including bellhousings (plus spares). I elected to go the 11" clutch route. It was an easy choice for me.

By the way, a little-known fact is that all L-78s DID NOT use the lightweight 12-3/4" flywheel with 10-1/2" clutch. All Corvette L-78s did, but not all L-78s were installed in Corvettes. Far more were installed in 66-70 Chevelles and Camaros. Those applications all used a 14" flywheel with 11" clutch.

[Mark S. Lovejoy]

Re: Joe;

Joe,

Thanks for the info, just so I understand it correctly; GM PART #14085720 and a 11" clutch is what we need for the '65 L-78 under construction.

"It's a very popular retrofit flywheel, though, for folks that want a lightweight flywheel (I'm not one of them). It will fit any internally balanced, 2 piece rear seal big block or small block. It's still available under GM PART #14085720."

Thanks again...Mark

[Joe L.]

Re: Joe;

Mark-----

The GM #14085720 is the current replacement part number for the flywheel originally used on the 1965 Corvette L-78. It may or may not still carry the 3856579 casting number. If you purchase one, I'd be interested in finding out what the current number on them is.

The 14085720, as well as the original flywheel, are NOT configured for use with an 11" clutch. This flywheel, just like the original, is a 12-3/4" flywheel designed for use with a 10-1/2" clutch. It cannot be used with an 11" clutch.

The original clutch used for 1965 L-78 applications was basically the same as the clutch used for 63-68 Corvette 327 applications. So, while the flywheel was different than the 327 flywheel ("lightweight" versus "standard weight"), the clutch assembly was pretty much the same.

It was NOT the same for L-88/ZL-1 and 1970-72 ZR-1 applications, though. Those applications, while using the same flywheel as the 1965 L-78, used a different and heavier duty 10-1/2" clutch, including both pressure plate assembly and friction disc.

[Mark S. Lovejoy]

65 Flywheel

Joe,

Great information as usual, you never cease to amaze me with the data you have.

When I get the part in hand I'll send you the numbers.

Best Regards,

Mark