C1 Clutch and Flywheel Question

[Mark P.]

I need a flywheel for my 1960 4sp 245hp and decided to go with a Hays 10-130 billet steel flywheel which is a 30lb 168 tooth, 14" flywheel that is drilled for both the 10.5" and 11" clutch. In other threads in the TDB it was stated that the 1960 model came with "a 28lb, 14", 168 tooth flywheel of GM casting #3729004" which has been discontinued.

I also read on the TDB that the aluminum bellhousing used in 1960 was meant for the 168 tooth flywheel with a 10.5" clutch disk.

After calling Hays, Summit, Luk and Paragon I am still not 100% sure if this flywheel and a 10.5" Luk clutch set (04-0421, which is what Paragon is likely selling) is a good choice for a stock feel clutch.

Does this make sense ?

[Joe L.]

Re: C1 Clutch and Flywheel Question

I need a flywheel for my 1960 4sp 245hp and decided to go with a Hays 10-130 billet steel flywheel which is a 30lb 168 tooth, 14" flywheel that is drilled for both the 10.5" and 11" clutch. In other threads in the TDB it was stated that the 1960 model came with "a 28lb, 14", 168 tooth flywheel of GM casting #3729004" which has been discontinued.

I also read on the TDB that the aluminum bellhousing used in 1960 was meant for the 168 tooth flywheel with a 10.5" clutch disk.

After calling Hays, Summit, Luk and Paragon I am still not 100% sure if this flywheel and a 10.5" Luk clutch set (04-0421, which is what Paragon is likely selling) is a good choice for a stock feel clutch.

Does this make sense ?

Mark-----


The original clutch used for all C1 Corvettes was a "3 finger" (coil spring) type clutch. All of the LUK clutches that I'm aware of (including 04-0421) are DIAPHRAGM SPRING type clutches. These will actually provide a softer clutch pedal with equal engagement force. Some problems have been reported when using a diaphragm spring clutch on C1 involving the pedal "sticking to the floor" under certain conditions. However, I think this problem is manageable.

All C1 bellhousings, cast iron or aluminum, are designed for 14", 168 tooth flywheels. A 10" or 10-1/2" clutch will work without problem. I've been told that an 11" clutch will fit, too, but I've never confirmed that.

[Mark P.]

Re: C1 Clutch and Flywheel Question

Joe - since I am looking for a softer feeling clutch than the original 3 finger then the multifinger seems right for me.

Any issues with the Operation Test or a Performance Verification if I go with the softer feeling clutch ?


Thanks,

Mark

[Joe L.]

Re: C1 Clutch and Flywheel Question

Joe - since I am looking for a softer feeling clutch than the original 3 finger then the multifinger seems right for me.

Any issues with the Operation Test or a Performance Verification if I go with the softer feeling clutch ?


Thanks,

Mark

Mark-----


That I do not have an answer for. Someone else involved in judging should know, though.

[Jerry G.]

Re: C1 Clutch and Flywheel Question

Since this is a technical board I am curious about a technical clutch issue. Why not use a double or triple disk clutch such as a Tildon setup. For racing we try and lower the inertia so the engine spins up faster. We use lightweight flywheels and small (7.25 inch diameter clutches). They can take very large amount of power, over 800 HP, and seem to hold up very well and have very light pedal pressure. I was thinking of using this setup in my 61 FI car. Just curious. Jerry

[Joe L.]

Re: C1 Clutch and Flywheel Question

Since this is a technical board I am curious about a technical clutch issue. Why not use a double or triple disk clutch such as a Tildon setup. For racing we try and lower the inertia so the engine spins up faster. We use lightweight flywheels and small (7.25 inch diameter clutches). They can take very large amount of power, over 800 HP, and seem to hold up very well and have very light pedal pressure. I was thinking of using this setup in my 61 FI car. Just curious. Jerry

Jerry-----


My guesses would be:

1) Cost;

2) Uncertainty that the product would be all-around satisfactory after installation;

3) Poor cost to benefit ratio for STREET applications.

[Jerry G.]

Re: C1 Clutch and Flywheel Question

Your probably right about the cost issue. They are more expensive,BUT small blocks really love to rev up quick when you use them. Yeh Ha

[Joe L.]

Re: C1 Clutch and Flywheel Question

Your probably right about the cost issue. They are more expensive,BUT small blocks really love to rev up quick when you use them. Yeh Ha

Jerry-----


They rev quicker if one uses an aluminum flywheel, too, but you'd NEVER catch me using one.

[Mark P.]

Re: C1 Clutch and Flywheel Question

I decided to go with a 10" AC Delco 3 finger clutch kit.

Thanks,

Mark

[John H.]

Re: C1 Clutch and Flywheel Question

I've used several of the Paragon (LuK) diaphragm clutches with the original 3729004 flywheels on my C1's, and the combination is outstanding; GM knew what they were doing when they dumped the old-tech Borg & Beck 3-finger clutches after 1962.

[Duke W.]

Re: C1 Clutch and Flywheel Question

I never had any problems with the OE diaphragm clutch including some drag racing and race track hot lapping. I was aware of the "sticks-on-the-floor" issue, but it never happened to my 327/340 SWC. It could be that a C1, which was originally designed for a three-finger type needs some sort of overcenter spring or stiffer return spring. The C2 release system appears to have adequate overcenter restoring force in the pushrod spring - the one from the dash to the cross shaft.

AFAIK the Luk replacement is essentially the exact same design as the OE diaphragm type and should be perfectly adequate for any reasonable street use and light racing. OE clutch clamping force specs varied slightly over the years and big blocks had a bit more than SBs along with larger diameter (except L-88).

The '67 AMA specs list the clamping force of the 327 clutch as 2100-2300 pounds, 2450-2750 for L-36/68 and 2600-2800 for L-72 (no specification for L-88). The torque capacity of the 427 clutches are greater than just the increase in clamping force would indicate because they are larger diameter.

I don't have a spec for the Luk 10.5 and 11" replacements.

The only option to consider IMO is replacing the OE gray iron 33 lb. SB 153 tooth flywheel with the nodular iron 18-pound L-88 flywheel, but I only recommend this option for consideration with SHF/FI engines and a 3.70 or shorter axle. I do know of one individual who did this with a "327 LT-1" engine, and after getting accustomed to it, he said it was fine for normal use. He later replaced the 4.11 axle with a 3.36 and again said it was satisfactory in normal driving.

A low inertia dual disk clutch that will handle 600 lb-ft and safely rev to 10,000 is way overkill for any street application, and the money is much better spent on head massaging and upgrading connecting rods. A "tricK" clutch is only worthwhile if your car is meant for serious racing. (As a technical point of interest, clutches (and transmissions) are rated by maximum input torque capacity and maximum RPM, not horsepower. For example the clutch design for a diesel engine rated at 800 HP @ 1800 RPM would be very different than a small block rated at 800 HP @ 9000 RPM. The diesel clutch would have to handle nearlly 2500 lb-ft of torque, but low RPM. The racing small block would only have to handle about 500 lb-ft, but much greater revs.)

I don't have any experince with C1 clutches, but given John Hinckey's advice, I would use the diaphragm type in a C1 and stay away from the OE three-finger type, but you may need to evaluate and improve the OE external return spring system to prevent hangup. I can offer no advice because I'm not familiar with the details of the design.

Diaphragm clutch hangup can also be solved or mitigated by careful clutch freeplay adjustment. If hangup is a problem increase the freeplay to the maximum amount without clutch drag. This will help prevent the diaphragm spring from being pushed "over center", which is the root cause of high rev diaphragm clutch hangup.

As far as PV is concerned, the judge doesn't operate the clutch, so there's no way he can know what's installed. The diaphragm type should provide lower effort for the same clamping force, and be much more pleasant in typical around town driving where you do a lot of shifting.

Duke

[Joe L.]

Re: C1 Clutch and Flywheel Question

I never had any problems with the OE diaphragm clutch including some drag racing and race track hot lapping. I was aware of the "sticks-on-the-floor" issue, but it never happened to my 327/340 SWC. It could be that a C1, which was originally designed for a three-finger type needs some sort of overcenter spring or stiffer return spring. The C2 release system appears to have adequate overcenter restoring force in the pushrod spring - the one from the dash to the cross shaft.

AFAIK the Luk replacement is essentially the exact same design as the OE diaphragm type and should be perfectly adequate for any reasonable street use and light racing. OE clutch clamping force specs varied slightly over the years and big blocks had a bit more than SBs along with larger diameter (except L-88).

The '67 AMA specs list the clamping force of the 327 clutch as 2100-2300 pounds, 2450-2750 for L-36/68 and 2600-2800 for L-72 (no specification for L-88). The torque capacity of the 427 clutches are greater than just the increase in clamping force would indicate because they are larger diameter.

I don't have a spec for the Luk 10.5 and 11" replacements.

The only option to consider IMO is replacing the OE gray iron 33 lb. SB 153 tooth flywheel with the nodular iron 18-pound L-88 flywheel, but I only recommend this option for consideration with SHF/FI engines and a 3.70 or shorter axle. I do know of one individual who did this with a "327 LT-1" engine, and after getting accustomed to it, he said it was fine for normal use. He later replaced the 4.11 axle with a 3.36 and again said it was satisfactory in normal driving.

A low inertia dual disk clutch that will handle 600 lb-ft and safely rev to 10,000 is way overkill for any street application, and the money is much better spent on head massaging and upgrading connecting rods. A "tricK" clutch is only worthwhile if your car is meant for serious racing. (As a technical point of interest, clutches (and transmissions) are rated by maximum input torque capacity and maximum RPM, not horsepower. For example the clutch design for a diesel engine rated at 800 HP @ 1800 RPM would be very different than a small block rated at 800 HP @ 9000 RPM. The diesel clutch would have to handle nearlly 2500 lb-ft of torque, but low RPM. The racing small block would only have to handle about 500 lb-ft, but much greater revs.)

I don't have any experince with C1 clutches, but given John Hinckey's advice, I would use the diaphragm type in a C1 and stay away from the OE three-finger type, but you may need to evaluate and improve the OE external return spring system to prevent hangup. I can offer no advice because I'm not familiar with the details of the design.

Diaphragm clutch hangup can also be solved or mitigated by careful clutch freeplay adjustment. If hangup is a problem increase the freeplay to the maximum amount without clutch drag. This will help prevent the diaphragm spring from being pushed "over center", which is the root cause of high rev diaphragm clutch hangup.

As far as PV is concerned, the judge doesn't operate the clutch, so there's no way he can know what's installed. The diaphragm type should provide lower effort for the same clamping force, and be much more pleasant in typical around town driving where you do a lot of shifting.

Duke

Duke-----


Big blocks didn't always have greater clamping force clutches than small blocks. For the 1965-68 period, they did. But that changed.

For 1969-71 all small blocks (except ZR-1) used an 11" clutch. This clutch pressure plate was GM #3893236 and was the same as the 66-68 L-36/L-68 unit.

For 1972-80, most small blocks (except ZR-1 and 1978-E79 L-48) used the former L-72 and L-71 11" clutch pressure plate, GM #3884598. This pressure plate also became the SERVICE unit for the above referenced 1969-71 applications and 66-67 L-36/L-68 applications described above when the GM #3893236 was discontinued in December, 1971.

All 1969-81 Corvettes (except L-88/ZL-1 and ZR-1) used a 14" flywheel.

All 1967-80 Corvettes with 14" flywheels (except 1969 MA-6, 1971 LS-6 and 1978-E79 L-48) used clutch disc GM #3908960. 1966 L-36 and L-72 used GM #3869183 which was discontinued and replaced for SERVICE by the GM #3908960 in January, 1968.

So, what this all boils down to is that all 1972-80 small blocks (except ZR-1 and 1978-E79 L-48) had the exact same clutch system as 1967-69 SHP big blocks.

[Bill M.]

Re: C1 Clutch and Flywheel Question

I never had the problem, but I recall that the clutch sticking to the floor with a diaphragm clutch occurred on on pressure plates that had straight fingers. When the clutch pedal was depressed, the centrifugal force acting on the fingers at high rpm overcame the spring's restoring force. When the rpm came down, the clutch pedal would snap back.
Once the design was revised so that the fingers were bent toward the release bearing, that problem was cured. when the clutch pedal was depressed, the fingers never got to a position where the centrifugal force on the fingers worked against the spring's restoring force

[John H.]

Re: C1 Clutch and Flywheel Question

Once the design was revised so that the fingers were bent toward the release bearing, that problem was cured. when the clutch pedal was depressed, the fingers never got to a position where the centrifugal force on the fingers worked against the spring's restoring force

Correct! All '63-up Corvette applications used the bent-finger diaphragm configuration, while many passenger cars used the flat-finger configuration (and the longer 1-3/4" throwout bearing).