65 327/350 A/C Convertible terrible shudder when the clutch is let out

Q. I have a 65 327/350 A/C Convertible that I’ve had and babied for 25 years. A stunning show car. I finally had the engine out for a rebuild last year and had the transmission rebuilt too with a new clutch. I’ve been through 3 clutches in less than 200 miles. Each one with the same problem. A terrible shudder when the clutch is let out. When I have to slip the clutch to get up the incline of my driveway and slowly go into my garage, it vibrates like it’s going to shake itself apart. After the third clutch was put in, the transmission guy told me it just needs to break in. This does not seem normal. I did not have that problem previously. The brand of clutch that was installed was Luk. I was told that the flywheel was machined. And an engine mount replaced. Anyone have any ideas?

A. I think you’re looking at the wrong parts. Here in the shop we have ceased machining flywheels unless there is absolutely no alternative. We have had so many problems (mostly like yours) that we consider it cost prohibitive. When a flywheel is machined it has to be absolutely perfect or the clutch will shudder.

Consider that when you set the flywheel up in the lathe that it must be checked multiple times to be sure there is no run-out. In most cases this requires a mounting hub to bolt the flywheel onto. That hub has to have as close to zero run-out as possible and is often measured on the order of one ten thousandth of an inch rather than one thousandth of an inch.

Originally posted on National Corvette Owner’s Association newsletter http://www.nationalcorvetteowners.com/

As little as on thousandth of one inch at the center of the flywheel can equal several thousandths of an inch at the outer edge of the contact surface. To understand the principal for all those who were not trig masters in school put a ruler on your desk and lift one end while the other rests on the desk. As you look at the gap you see it increases as you move farther away from the point where it touches the desk. This is the same thing that happens when you have a tiny variance at the center of a flywheel.

So remove the tranny again and measure run-out relative to the crank shaft and don’t be surprised if it exceeds the allowable limit. If the run-out is out of spec remove the flywheel and carefully check the end of the crankshaft including measuring run-out and any signs of nicks, dents burrs, etc.

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