C2 clutch

[brumbach]

Hope you can help me with this one. I bought my 65 vette a year ago. The previous owner had the clutch replaced at the time of purchase. He said the old one was fine but making a noise so he replaced it. My initial test drive took place at the garage where the clutch was installed. The previous owner paid the bill and passed the invoice to me for my records.

Approximately a month later as I prepared to depart from a Sonic drive-in, I started the car, depressed the clutch pedal, slipped the car in reverse, and a loud grawling noise that seemed to come from the clutch. I clearly could feel a corresponding fibration in the clutch pedal. I immediately pulled the car out of resverse, released the clutch and the noise stopped. I depressed the clutch, shifted in reverse again, and there was no noise. The car operated fine for the rest of the day. Some months later, the same happened again but this time while setting at a red light. The only difference was that I was in first gear, with the clutch depressed awaiting the light to change. I placed the car in neutral, released the clutch, and the noise stopped. I then re-engaged first gear, leaving the clutch depressed and the noise stopped.

After the episode at the traffic light, I scheduled a visit to a local mechanic but could not get the car to do it again. By the way, I bought the car in Atlanta, Ga and live in Kentucky so returning the car to the shop that replaced the clutch was not an option. The mechanic know where to begin since the car was acting okay. I suggested the throwout bearing but he said that would only occur when the clutch pedal was out...not when it was depressed. He speculated that maybe the clutch was going through a breaking in period. Never heard of a break-in for a clutch!

This morning, after several months since the last occurance, it happened again. I can now make it happen at will, as opposed to it occurring without warning. Don't know it the situation is worsening but at least I should be able to get it to repeat for a skilled mechanic to witness. To get it to occur, I do the following: Hold the rpm between 1500 - 2000 and depress the clutch pedal. I might have to move the clutch pedal in and out a little but the noise will return. If I have the car in gear at the time, I can feel a accompaning vibration in the gear shift with the noise. As I said, the noise is a grawling (or moaning) sound with a varying pitch.

Any thoughts as to what is going on?

 

[JohnZ]

It's either the pressure plate or the throwout bearing, and/or the throwout bearing I.D. is chattering on the bearing retainer O.D. as it moves in and out due to no lube in the groove in the bearing I.D., or it could be a worn pilot bushing. Do you know what kind of clutch the shop installed and whether the throwout bearing and pilot bushing were also replaced?

 

[brumbach]

The bill doesn't state the type of clutch. You suggest possibly the throwout bearing. The mech I talked to with the first occurance said the throwout bearing, if bad, would be sounding off with the clutch pedal out, not in. Is he wrong?

It's either the pressure plate or the throwout bearing, and/or the throwout bearing I.D. is chattering on the bearing retainer O.D. as it moves in and out due to no lube in the groove in the bearing I.D., or it could be a worn pilot bushing. Do you know what kind of clutch the shop installed and whether the throwout bearing and pilot bushing were also replaced?

 

[studiog]

I had a similar experience years ago in my 64 Vette. Hard to describe the noise... sounded like a sick horn blowing but not as loud. It did turn out to be the throwout bearing.

 

[brumbach]

Your description of "sick horn" is a better example of what's happening with my 65. When did it make the sound? Was it when you had the clutch pedal depressed?

I had a similar experience years ago in my 64 Vette. Hard to describe the noise... sounded like a sick horn blowing but not as loud. It did turn out to be the throwout bearing.

 

[studiog]

As best as I can remember it made the noise in the beginning of the travel when stepping on the pedal and sometimes constantly when stepping on the pedal. It would come and go. I think your mechanic may be talking about more of a soft chatter sound that you can hear when your foot is off the clutch. A completely different sound altogether and maginally noticeable. Good luck.

 

[JohnZ]

The bill doesn't state the type of clutch. You suggest possibly the throwout bearing. The mech I talked to with the first occurance said the throwout bearing, if bad, would be sounding off with the clutch pedal out, not in. Is he wrong?

When the clutch pedal is out (up against its stop bumper), the throwout bearing isn't touching anything and isn't rotating, so it can't make any noise. It will only make noise when you push on the pedal so it contacts the clutch fingers. Proper clutch adjustment (pedal free play) is critical to throwout bearing life - if you don't have correct pedal free play, the bearing will be touching the clutch fingers all the time, which will fry it in short order.

 

[brumbach]

Short order...how short order? I'll certainly check the free play and make sure it's correct but if not, the clutch (with new throwout bearing) has approximately 1000 miles on it. Would it, or could it burnout in this length of time?

When the clutch pedal is out (up against its stop bumper), the throwout bearing isn't touching anything and isn't rotating, so it can't make any noise. It will only make noise when you push on the pedal so it contacts the clutch fingers. Proper clutch adjustment (pedal free play) is critical to throwout bearing life - if you don't have correct pedal free play, the bearing will be touching the clutch fingers all the time, which will fry it in short order.

 

[JohnZ]

It's highly unlikely that a properly-installed clutch or throwout bearing would go south with only 1000 miles on it, if the throwout bearing was installed correctly on the clutch fork (the design allows it to be done wrong, which makes it impossible to get the clutch linkage adjusted properly) and the linkage was adjusted with the correct pedal free play. If there was inadequate free play in the initial adjustment (should be 1" to 1-1/2" of pedal movement from the up-stop to the point where you feel resistance from the throwout bearing when you push on the pedal) or the return spring is missing, it could easily fry the throwout bearing in less than 1000 miles.

 

[brumbach]

I'm now reasonably convinced that the problem is within the throwout bearing. I guess the only way I'm gonna know for sure is to tear things down. Haven't done it before but will take my time and follow closely the tech manual. Before I do, I have another question. In searching the web for other diagnostic suggestions, I discovered that some throwout bearings should be lubricated periodically (every 6 months or so). Have I been remiss in lubing mine? If so, how is this done? The article seemed to indicate lubing the bearing can be done without any disassembly. Your thoughts, please.

It's highly unlikely that a properly-installed clutch or throwout bearing would go south with only 1000 miles on it, if the throwout bearing was installed correctly on the clutch fork (the design allows it to be done wrong, which makes it impossible to get the clutch linkage adjusted properly) and the linkage was adjusted with the correct pedal free play. If there was inadequate free play in the initial adjustment (should be 1" to 1-1/2" of pedal movement from the up-stop to the point where you feel resistance from the throwout bearing when you push on the pedal) or the return spring is missing, it could easily fry the throwout bearing in less than 1000 miles.

 

[JohnZ]

The rotating portion of throwout bearings are permanently lubricated and sealed and require no periodic maintenance. Lubrication is important at assembly, however, in the groove on the O.D. of the bearing where the fork and spring goes, and in the groove in the I.D. of the bearing so it slides freely on the transmission bearing retainer (this is shown in the Assembly Manual). It's also important to lube the end of the clutch fork ball stud and the recess it fits into on the clutch fork; all of the above require gray moly lube. Make sure you get the correct (1-1/4" long) throwout bearing, not the 1-3/4"-long one, and when you assemble it to the end of the clutch fork, make sure both the ends of the fork AND the flat tension spring are in the groove around the O.D. of the bearing; it's possible to "capture" the flange on the rear of the bearing assembly in the "curls" on the end of the fork, and that will prevent you from being able to adjust the clutch linkage with proper pedal free play.

 

[allcoupedup]

from LUK's website: