11" Clutch

[Clark D.]

Picked up a 66 coupe about 6 weeks ago and I am starting to go through everything. The clutch appears to be a 11" with a 621 bellhousing. Did the 66's ever come with a 11 clutch? This is a late 66, made in June of 66.

[Michael H.]

Re: 11" Clutch

Clark,

1966 Corvetes that were originally equipped with 427 engines would have had 11" clutches. What side is your hood support on?

[Joe L.]

Re: 11" Clutch

Clark-----

1966-68 Corvettes with 427 were the only 63-68 Corvettes that ever used an 11" clutch (except 67-68 L-88). ALL other 63-68 Corvettes, including 67-68 L-88, used a 10" or 10.4" clutch.

While 1966 Corvettes with big block did use an 11" clutch, they did not originally use the GM #3899621 bellhousing. ALL 1966 Corvttes with big block used bellhousing GM #3872444. The 3872444 was used for very early 67 big blocks, too. Later 1967 through 1981 applications with 11" clutch (and, 10" dual disc clutch) used bellhousing GM #3899621.

[Mike M.]

Re: 11" Clutch

i've judged late 66 big blocks with 621 bells where owner swore the 621 was original. i agree with joe however believing the 444 bell is appropriate for all 66 mark 4 equipped vettes. mike

[Clark D.]

Re: 11" Clutch

Michael;

To you question, the hood support is on the right hand side, Passinger. I don't think the car was ever a big block. I have seen threads in other chat rooms stating the 621 could have been used on small blocks back to 66. However, you guys are the experts.

[Michael H.]

Re: 11" Clutch

Thanks Clark. That's what I was wondering. The hood support is an easy/quick way to tell an original big block car without having to dig into details. Sounds like someone added the entire 11" clutch assembly from a later car.

[Joe L.]

Re: 11" Clutch

Clark------

I can absolutely guarantee you that the GM #3899621 bellhousing was never originally used on 1966 Corvette small blocks. This bellhousing didn't even exist until late 1966. Also, as far as Corvettes go, no 1963-68 small block ever received a 14" flywheel with 11" clutch.

[Joe L.]

Addendum

Clark------

A little more information now that I have a few extra minutes. Although an 11" clutch was not used in any Corvette before 1966 and was never used for ANY pre-1969 Corvette small block, 11" clutches WERE USED for other Chevrolets beginning in about 1964 and that may cause some of the confusion. Models included full size passenger cars with big blocks (409, 427 and 396), some small block-equipped passenger cars, and most passenger cars with HD clutch (like taxis, police cars, etc.). These applications used a 14" flywheel with an 11" clutch. The GM #3899621 bellhousing was never originally used on any 64-66 application, although later it became the SERVICE bellhousing for all of these.

The original, "full-round", die cast aluminum bellhousing used for 1964 14" flywheel (i.e. as used with 11" clutches) applications was GM #3843941. In July, 1965 that bellhousing was discontinued and replaced by GM #3866982. In November, 1965 it was discontinued and replaced by GM #3872444 and, finally, in November, 1966 the 3872444 was discontinued and replaced by the 3899621.

The GM #3872444 and GM #3899621 were the only "full-round" bellhousings for 14" flywheels (i.e. as used with 11" clutches) which were ever used in Corvettes, though. The 3843941 and 3866982 "reigned" during a period when Corvettes didn't use 14" flywheels. I wouldn't discount the remote possibility that some very early 1966 Corvettes with big blocks used the 3866982, though.

[Clark D.]

Re: Addendum

Joe;

Thanks for the very informative update. I appreciate you taking the time to research and share the data. Thanks Again.

[Joe L.]

Re: Addendum

Clark------

It didn't take too much research. I only needed to look up/confirm the part numbers for the earlier 2 bellhousings. The rest of it I already knew, but I didn't have time to get into it in my previous response.