R66

Went through the stash of 50 years + and found a perfect 11" flywheel (168 tooth), new 11" clutch disc, and 1 new and 2 good pressure plates that I forgot I had from racing a V-8 Vega. (I used to change the clutch and PP every racing season) I also have two 11" bell housings and a couple of starters to make it all work with no additional investment.

I have a new (but 20 years old) RAM 3 finger Borg and Beck PP and two very good (slightly used) GM diaphragm PPs. Don't know which to chose.

The stock 10 1/4" diaphragm setup is perfect for my old legs and current driving habits, but I am anticipating having to buy a new PP and grinding the flywheel ($$$$ out of the fragile retirement budget) if I stick with the 10 1/4".

The problem is, if I replace the 10 1/4" with an 11", is the petal pressure going to be stiffer than the 10 !/4" and my old leg. I can't compare with the Vega as I was 20 to 40 something when I raced it some two and a half decades ago. :total:

Also, if I go with the 11" flywheel and PP, which is heavier that the 10 1/4", should I go with a different heavier harmonic balancer to offset any torsional twist in the crankshaft from the heavier clutch setup???

Not worried about numbers and not twisting the wrinkle wall slicks anymore. Just a driver and loving it between twisting the wrenches.

JohnZ

Most aftermarket 11" clutches have a higher pedal pressure requirement than their production 10.5" brethren, although it's not always the case. If it has a "hot-rod" brand name (Zoom, Ram, etc.), it's likely to require higher pedal pressure.

The harmonics, excursions, and natural frequency variations and tuning of harmonic dampers is way above my pay grade - just stick with what the OEM used on the high-performance versions of that engine and you'll be fine, for a street engine.

R66

Thanks John.
It appears you are one of the experts on the forum. Thank you for taking time to respond. You have confirmed my thoughts. I may try to sell the 11" stuff and buy new 10 1/4" for the car, the conservative way to go.
Ron

DansYellow66

I'm not so sure the leg effort on an 11 inch stock diaphragm clutch is higher than that of a stock 10-1/2 inch diaphragm clutch. I believe the additional torque capacity comes from the larger surface area - at least with stock units. A diaphragm clutch should be easier on the leg than a 3 finger B&P unit. If you really have to have a light pedal pressure due to leg problems you might look at the McLeod twin-disc clutches - but they are pricey.

wmf62

my experiences....

a Borg & Beck PP has higher leg requirements than a diaphragm PP.

that said, I have an 11" diaphragm LUK clutch assembly in my 62 behind a ZZ4 with no problems/discomfort.

Bill

rfn026

I can't address the clutch issues but I can add something on the harmonic damper.

I would stay with the stock GM damper but use a brand new one. All of the aftermarket dampers have issues The Fluidamper units have to be replaced on a regular basis. They deny this but all of the NASCAR teams treat them as a disposable item.

"A few years back GM ran a series of test using a 427-cubic-inch small block. From 3,000 rpm to approximately 6,500 rpm all of the dampers tested limited crankshaft twist to no more than 0.6 degrees. Above 6,500 rpm things got interesting. At 7,800 rpm one damper allowed a rather considerable 2.0 degrees of crank twist. The second damper they tested allowed 1.7 degrees of twist, and the third had allowed 1.25 degrees of twist. And these were all brand new units.

You’re in even bigger trouble if you use a 20-year-old damper. Over time the rubber layer deteriorates causing the outer part of the damper to shift. The outer balance ring actually shifts out of position over time."

Here's the complete article.


This is from one of the Lightweight Grand Sports

Richard Newton

R66

FYI,
I checked the RAM website, and they say the Borg and Beck using springs will require more pedal effort than the diaphragm. I am guessing the 11" diaphragm will also require more effort than the 10 1/4" diaphragm. Makes sense. I remember having to reinforce the clutch arm and rod both on the race car as they were bending on me using a B&B 11".
rfn 026, great info on the damper. I always believed GM used what was best for the application. Not always right, but a safer bet.

ILBMF

I have a McLeod twin disc in my 700 hp Mustang and the pedal feels like a Ford Focus, grips excellent. When I reassemble the drivetrain in this '66 I will be looking into a McLeod twin if they are available for this application

babbah

I have been running a Fluiddamper on
my 67 Big Block for the past 10 years with zero issues.

Pop Chevy

The NASCAR racers change everything on a regular basis. There's too much at stake.
Besides, they are spinning those engines to what, almost 9 grand lap after lap ? Fluidamper is a good unit.
However, I don't believe the flywheel size will affect damper size (unless you too are turning 9k). I would stick with a diaphragm clutch.

DZAUTO

THERE IS NO SUCH THING AS AN 11in FLYWHEEL!!!!!!!!!!!!!!!!
But there is such a thing as an 11in clutch.

R66

Good correction DZAUTO, as I have a 168 tooth flywheel drilled only for a 10 1/4" pressure plate/clutch disc and another drilled for the 11" pressure plate/clutch disc. Others were drilled for both the 10 1/4" and 11" discs.
Technical, but correct. The 153 tooth flywheel will utilize either a 9" or 10 1/4" clutch disc (I have a couple of those also).
I should be comparing the 10 1/4" clutch/pressure plate to the 11" clutch/pressure plate. My original intent.
Thanks for the input
Ron

DZAUTO

EVERYTHING I own (that is, in the way of early Chevy products-------------and my Cutlass), has, or has been changed to, the larger 168 teeth flywheel so that an 11in clutch can be used. I realize that ALL 63-65 Corvettes came with ONLY the smaller 153 teeth flywheel and 10in clutch. But If I had one, it would get a 168 teeth flywheel and 11in clutch----------------originality be damned. And yes, I realize this would also require changing the starter.
Now, with that said, I HATE starters for 153in flywheels for one specific reason. If and when the time comes to drop the oil pan on an engine with the 153 teeth flywheel-----------------IT REQUIRES REMOVING THE STARTER!!!!!!!!!!!!!!! The reason for removal of the starter is because the starter on a 153 teeth flywheel covers up the two right rear pan bolts!

skunk22

Did we ever get an answer to the hard pedal pressure. I am having the same problem. I have replaced every component and still have a pedal I have to push with my heal because it is so hard. Used all standard 11" NAPA clutch pressure plate and flywheel. New push rods z bar and fork. The push rod is in the correct place. 66 vette 427 all stock. Any help ???
Skunk

R66

From my research here on the forum and at various pressure plate manufacturer's web sites, the stock diaphragm type 11" pressure plate will have a higher pedal pressure than the 10 1/4" as it takes more pressure to hold the larger surface area of the single disc 11" clutch.
The Borg and Beck 3 finger pressure plate requires even greater pedal pressure as the springs are heavier to give an even greater clamping force.
I am failing conservatively and going to buy a new 10 1/4" diaphragm pressure plate even though I have a couple of new 11" setups under the bench. I retired the slicks and race engines and now just enjoy cruising with a few hole shots now and then.

It sounds like you are already there with the 11" setup. About the only thing you might do is make sure the bell crank is lubricated. Maybe go to a hydraulic clutch setup?? :total:

Ron

DZAUTO

Hmmmmmmmmmmmmmm, I have an 11in clutch in all my cars (more or less stock diaphragm) with bone stock factory clutch linkage, I'm 73yrs old with total knee replacement on both knees, and I don't notice any excess effort to depress the clutch pedal in any of the cars (76 Cutlass w/455, 70 Chevelle w/SB400, 56 Vette w/SB400, 51 Chevy w/383, 68 Chevelle w/350).
You guys MUST BE wimps!

ILBMF

I drive 4 different standard shift vehicles and I don't even think about clutch pedal weight. I do hate traffic backups though.

R66

Guess you are right DZ, I haven't had my knees replaced yet nor my back worked on. Wimp as I am, I'm 5 years behind you. The surgeon recommends waiting as long as I can as he says arthritis will set in on joints they cut on.
I am also concerned about moving the starter out closer to the exhaust pipe. Could probably solve it with a heat shield, but that can be a hassle too.

Ron

wmf62

no heat shield and no problems, same starter for 40 years; but maybe i'm just lucky.....

heat shield can't hurt though...
Bill