C2/C3 - Clutch Kit Education

[Rory Riedy]

All,

Doing a frame off of a '66 Conv BB Muncie 4-speed. Would like to end up with a correct as possible driver to be proud of.

My engine however is a '68 numbers matching 427/390 that was originally setup with an auto trans. The setup as I took it apart was: a 12" Flywheel (153 tooth), 10 1/2" bellhousing, with a 10.4" 10 spline clutch, with the Muncie 4-speed.

Most of the parts books (Corvette Central, Corvette America, Mid-America Motor works, etc) reference a HD (Heavy Duty ?) 10.4", 10 spline clutch kit & a regular 10.4", 10 spline clutch kit that were both used & are available.

Can some one explain to me the difference between the HD & the "regular" clutc & how I can tell which I have/need?

I have been told to use an AC Delco Clutch kit #381146. But I can't get any information to tell me if this is for the HD usage or not.

Would this AC Delco Clutch Kit be the correct kit or is there another one for the HD application?

Would also appreciate any other recommedation you might have for a clutch kit &/or a vendor to purchase from?

As always THANKS for taking the time to help a novice hobbier.

Triple R

[Joe L.]

Re: C2/C3 - Clutch Kit Education

Rory-----

All Corvette big block applications, except 1965 L-78 and 1967-69 L-88, used a 14" flywheel. Except for 1969 wih MA-6 dual disc clutch and all 1971 LS-6, they also used an 11" clutch. 1965-70 big blocks used a 10 spline input and 71-74 used a 26 spline input.

Generally speaking, when a "HD" clutch for a Corvette is used and described as a 10-1/2" inch, they are talking about the 67-69 L-88 clutch. This clutch is no longer available from GM and I don't think it's available in reproduction or replacement, either. The 1965 L-78 clutch, the only other big block that ever used a 10-1/2" clutch was the same as 63-67 small block, although the flywheels were different.

My recommendation to you is to use a 14" flywheel and 11" clutch. This will require a bellhousing for a 14" flywheel. 1966 Corvette big blocks used bellhousing casting #3872444. This is one of the most difficult and expensive of all Corvette bellhousings to find, though. You can also use a GM #3899621 which is virtually identical to the '444'. It's a lot more common, but they still run about 100 bucks, or more, in the used market.

The Delco #381146 is a 10-1/2" clutch with 10 spline disc. If you want to stay with the 10-1/2" clutch, this should work fine. The Delco #381258 is the 11" clutch with 10 spline disc. That would be a good one to use if you go with my recommendation to convert to the original size 11" clutch.

If you convert to an 11" clutch, you will also need a flywheel, in addition to the bellhousing I described above. The flywheel is GM #3991469. You can purchase an aftermarket-equivalent of this flywheel for a lot less than the GM piece, though.