Clutch Question

[Mark H.]

I have a 1964 convertible with a 327/300 engine. Transmission is a 1968 Muncie (an M-21 to be converted to M-20, but that's another story). Flywheel is a replacement -- 366861N - but the same original flywheel was used in Corvettes in 1964 and 1968. I don't remember the bellhousing number, but it is correct for 1964.

The LUK RepSet line lists two different clutches: 04-084 for 1964 and 04-021 for 1968. The only difference I can identify is the outside diameter. The 04-084 is 10" and the 04-021 is 10 3/8". (both have a 1 1/8" spline and 10 teeth).

Seems to me the extra surface area of the '68 clutch is the way to go, but was interested to see if anyone had a different view. Thanks.

Mark

[Joe L.]

Re: Clutch Question

I have a 1964 convertible with a 327/300 engine. Transmission is a 1968 Muncie (an M-21 to be converted to M-20, but that's another story). Flywheel is a replacement -- 366861N - but the same original flywheel was used in Corvettes in 1964 and 1968. I don't remember the bellhousing number, but it is correct for 1964.

The LUK RepSet line lists two different clutches: 04-084 for 1964 and 04-021 for 1968. The only difference I can identify is the outside diameter. The 04-084 is 10" and the 04-021 is 10 3/8". (both have a 1 1/8" spline and 10 teeth).

Seems to me the extra surface area of the '68 clutch is the way to go, but was interested to see if anyone had a different view. Thanks.

Mark

Mark------


All 1963-68 Corvette small block clutches were "10-3/8"" disc diameter. Officially, it was 10-13/32" or right at 10.4". These clutches are often described as being "10-1/2"", though.

C1 Corvettes used 10" clutches.

Correction:

I did some more checking. GM shows that 1964-E66 Corvette small blocks originally used clutch disc GM #3852458. GM shows this as being a 10" disc. This piece was discontinued in 1969 and replaced by GM #3927128 which is a 10-13/32" disc. Two more supercessions followed to GM #458629 and 14007393. I believe these are 10-13/32" discs, too.

I have many NOS Corvette clutch discs but, unfortunately, I do not have a GM #3852458 so I cannot confirm what its original OD was. However, if I were you and regardless of what the actual OD was of the original 1964 clutch disc, I would use a 10-3/8" clutch disc now. It will be 100% compatible with your flywheel.

[Alan D.]

Re: Clutch Question

Bellhousing cast number is 3840383, on the side.

[Steven B.]

Re: Clutch Question

Mark------


All 1963-68 Corvette small block clutches were "10-3/8"" disc diameter. Officially, it was 10-13/32" or right at 10.4". These clutches are often described as being "10-1/2"", though.

C1 Corvettes used 10" clutches.

Correction:

I did some more checking. GM shows that 1964-E66 Corvette small blocks originally used clutch disc GM #3852458. GM shows this as being a 10" disc. This piece was discontinued in 1969 and replaced by GM #3927128 which is a 10-13/32" disc. Two more supercessions followed to GM #458629 and 14007393. I believe these are 10-13/32" discs, too.

I have many NOS Corvette clutch discs but, unfortunately, I do not have a GM #3852458 so I cannot confirm what its original OD was. However, if I were you and regardless of what the actual OD was of the original 1964 clutch disc, I would use a 10-3/8" clutch disc now. It will be 100% compatible with your flywheel.

Joe, you also recommend a 10 1/2 on a C1?

Steve

[Joe L.]

Re: Clutch Question

Joe, you also recommend a 10 1/2 on a C1?

Steve

Steve-----


GM never replaced the 10" clutch used for 1957-62 Corvettes with the larger 10-13/32" clutch. So, they never approved the use of the larger clutch for those C1 applications and I have no experience that would confirm that the larger clutch will work without problem. So, I can't say one way or the other.

Curiously, the 10-13/32" clutch is approved as a replacement for 1956 Corvettes.

[Ray K.]

Re: Clutch Question

Mark

All 327 engine Corvettes from 1963 -68 used the 10.5" (10 13/32) clutch disc.
The earlier part number was 3889344 and then was replaced by 3927128.
This disc was used with the 3841673 high performance diaphragm clutch cover and pressure plate assembly generally mated to a 3791022 flywheel inside of a 3858403 clutch housing (63-3788419). The disc #3852458 was
the 10" unit for 57-62 Corvettes with Dual 4BC or FI engines used with
3816144 pressure plate assembly which was a coil spring 3 finger unit.

Ray

[Joe L.]

Re: Clutch Question

Mark

All 327 engine Corvettes from 1963 -68 used the 10.5" (10 13/32) clutch disc.
The earlier part number was 3889344 and then was replaced by 3927128.
This disc was used with the 3841673 high performance diaphragm clutch cover and pressure plate assembly generally mated to a 3791022 flywheel inside of a 3858403 clutch housing (63-3788419). The disc #3852458 was
the 10" unit for 57-62 Corvettes with Dual 4BC or FI engines used with
3816144 pressure plate assembly which was a coil spring 3 finger unit.

Ray

Ray------


That's what I used to think, too, but I was wrong and, consequently, so are you.

The GM #3889344 clutch disc was a 10-13/32" disc but it was not used in PRODUCTION for all 1963-68 Corvettes. It came into use sometime in the mid 1966 model year. 1964-E66 Corvettes used clutch disc GM #3852458. GM says that the GM #3852458 was a 10" disc. But, was it actually a 10" disc? Well, guess what, I didn't think I had any NOS GM #3852458 discs but I was out looking for another part and guess what I found staring me in the face? THREE NOS GM #3852458 clutch discs. I was amazed to see them there myself. But, I measured them and GM is exactly correct---these are 10" clutch discs, NOT 10-13/32".

The GM #3927128 did replace the 3852458 for all 1963-E66 SERVICE in May, 1969 but, while the 3927128 was a 10-13/32" clutch, the 3852458 was a 10" clutch. By the way, the L66-67 and 1968 base engine clutch, GM #3889344 was replaced by the GM #3927128 in February, 1969. The GM #3927128 was used in PRODUCTION for 1968 L-79.

[Ray K.]

Re: Clutch Question

Joe,

And I believe that you are incorrect.

As I said the #3852458 disc was a 10' unit. This was used up through 1962.


The #3889344 was 10 13/32". The #3927128 was 10 13/32".
The #3889344 was replaced by 3927128 in Feb 69.
The disc #3845260 was the disc number prior to the #3889344. It was listed as 10.5" The #3845260 was replaced by #3889344 in Dec 66.

The #3852458 disc was also replaced by the #3927128 disc in 5-69. This was a good upgrade for service applications because both the flywheel and pressure plate would accommodate the the larger disc diameter resulting in more total surface area.

Ray

[Joe L.]

Re: Clutch Question

Joe,

And I believe that you are incorrect.

As I said the #3852458 disc was a 10' unit. This was used up through 1962.


The #3889344 was 10 13/32". The #3927128 was 10 13/32".
The #3889344 was replaced by 3927128 in Feb 69.
The disc #3845260 was the disc number prior to the #3889344. It was listed as 10.5" The #3845260 was replaced by #3889344 in Dec 66.

The #3852458 disc was also replaced by the #3927128 disc in 5-69. This was a good upgrade for service applications because both the flywheel and pressure plate would accommodate the the larger disc diameter resulting in more total surface area.

Ray

Ray------

I don't think so.

The GM #3852458 disc did not even exist in 1962 (or prior years). It is a 1964-released part number, so it could not possibly have been used in PRODUCTION for 1962 or earlier Corvettes. It was used in PRODUCTION for 1964-E1966 Corvettes with small block and it also became SERVICE for 1957-62 Corvettes after the original clutches used for those applications were discontinued.

GM #3845260 was not used in PRODUCTION for Corvette small blocks. It was released in 1965 for use on 1965 Corvette L-78. It is a 10-1/2" clutch. It was replaced by the GM #3889344 in December, 1966. The GM #3852458 was also replaced by the GM #3889344. So, BOTH part numbers GM #3852458 and GM #3845260 became GM #3889344. Then, GM #3927128 replaced the 3889344 in February, 1969.

In November, 1977 the GM #3927128 was replaced by GM #458629. The latter was discontinued without supercession in July, 1994.

Now, there's one other "gap" in the C2 small block clutch
usage sequence that we have not talked about. That was 1963. 1963 Corvettes used clutch GM #3815217, a 10" clutch according to GM. This clutch was a 1963-released part number and became SERVICE for 57-62 Corvettes. GM #3815217 was discontinued in August, 1965 and replaced by the GM #3852458 described above.

One slight correction: the GM #3845260 was not released for 1965 Corvette L-78. It was first released for use on 1964 full size passenger cars with 327 and 409. It was thereafter used on 1965 Corvette with L-78. It was never used for any C2 Corvette small block, though.