The Stovebolt Site Forums The Shop Area Driveline Help choosing a clutch size

It's time to put a clutch and flywheel into my rebuilt 235. I have two 168 tooth flywheels, one for a 10" clutch and one for an 11" clutch. The engine is a fresh rebuild with dual carbs/exhaust hooked to a T5 in a '50 3100. I don't plan to do any towing. The 10" clutch seems to be a little less common to find, I'm worried the 11" might be too grabby or hard to push (I drive in traffic a lot). Any insights on which to choose? Am I over thinking and should just grab whichever is nearer on the bench?

In my experience, the 11" one is not much more harder to push, just more friction surface.. driving in traffic shouldn't be worst. If you have the parts plus the parts aviability is better.... Why not??

ditto on J.F.'s reply

In my experience... the larger the disc the more chance you will get clutch chatter.
I always put the smallest disc I could in my customers jobs as a kind of insurance.
Now if you are pulling a heavy trailer I would go big.

It's possible the larger clutch will have the same, or possibly less pedal effort. With a larger swept areas on the flywheel and pressure plate, less spring pressure to clamp down on the disc will be required. That extra inch of diameter dramatically increases the square inch area and traction of the disc, so less clamping force will be needed. Some of the circle track cars we ran used a 7" diameter triple disc clutch to decrease the inertia of the rotating assembly and allow for quicker acceleration. Even with a hydraulic throwout bearing, the clutch pedal pressure was horrendous!
Jerry

I have the 11 inch and it is no problem to push in at all. My suggestion would be while it is apart to get the flywheel resurfaced by a professional who knows exactly what he/she is doing and how to do it so that hard spots (some call them hot spots) are no longer a problem for you. Hard spots will cause clutch grabbing. If your flywheel is resurfaced incorrectly, I've learned the hard way these spots can remain higher than the rest of the surface and nothing will have been solved. You'll see these as bluish or rainbow looking hard shiny areas on your flywheel...and I haven't seen very many used flywheels which are free of them. You may also see lines or cracks radiating outward in the clutch disc path and places where metal has checked or flaked. If you don't fix these, my experience is that within a few thousand miles (maybe less) you will have lots of chattering and grabbing. If you start with a flywheel that has been surfaced correctly, have no oil leaks to foul your clutch disc and go back with new disc, pressure plate and t.o. bearing (hint...Rock Auto has good prices), you should be good for years to come. The Chevy 11 inch flywheels I've seen tend to resurface nicely. I had mine done at Wade Transmission and Gear and it came out looking brand new.

The problem with most hard spots is that they're football-shaped, with most of the hardened metal below the surface. It's usually necessary to do a VERY deep cut to get rid of them. Simply grinding a hard spot flat doesn't remove it- - - -the metal around it will wear away and the high, hard area comes back and causes the clutch disc to wear and chatter.
Jerry

See Jerry's post above. That explanation is why I said you want somebody who knows exactly what they're doing. You want those hard spots gone and a shade tree fix can be a big waste of time and money.