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1967 Clutch Chatter

 
Old 04-13-2019, 06:36 PM
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CrystalRedZ
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Default 1967 Clutch Chatter

Hi all - looking for some advice. I have a 1967 L79/M21 coupe that I acquired in 2017. It has always had a clutch chatter when slowly engaging the clutch from a standing start and it can also be felt on gear changes. In addition, the clutch pedal has a slight vibration when driving (clutch fully released) and also makes a slight noise similar to a dry speedometer cable. The clutch pedal free play is adjusted correctly. The previous owner had the engine rebuilt and at the same time also installed a new clutch. It has about 2,500 miles on the rebuilt engine and new clutch, and I have put about 600 of those mile on it with no change in the chatter issue - if anything, maybe it has become a bit worse.

I suspected that perhaps the clutch fork was incorrectly installed onto the throwout bearing. So, I finally decided to bite the bullet and take the transmission and clutch assembly out. The throwout bearing was correctly installed on the clutch fork, but the throwout bearing is very sloppy. I measured .070" of radial play, and .025" of axial play in the throwout bearing. I suspect this is causing the pedal noise/vibration when driving, but not sure about the clutch chatter when engaging the clutch. Thoughts? The transmission input shaft pilot diameter measures 0.590" but I need to obtain an inside micrometer to measure the ID of the pilot bushing in the crankshaft to make sure the input shaft is properly supported.

I have attached photos of the components. I believe the flywheel, pressure plate, and clutch disc all look good, but let me know if you see anything or think otherwise.

Thanks!
Dave

Flywheel with clutch dust residue

Flywheel after wiping off clutch dust

Pressure Plate clamping surface

Clutch disc - trans side

Clutch disc - flywheel side

Valeo AMC-13 pressure plate (made in Korea)

Pressure plate

Throwout bearing - trans side

Throwout bearing - clutch disc side
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Old 04-13-2019, 07:19 PM
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We have been talking about this type issue for awhile, so a lot of info in the older threads if you go back and search.

For now I would:

1. Buy a new TO bearing. I recommend the all metal one with self-alignment feature. I can find the part number for you if needed.

2. Install a dial indicator on the engine block and check the flatness of the flywheel 360 degrees rotation. Do this at 3 or 4 different points outward along the radius (area where clutch disc will contact flywheel)

3. Remove flywheel or borrow one that you know if flat and install the pressure plate without the disc. Using a hydraulic shop press and TO bearing, push the TO bearing to open up the clutch. Lars has recommended this clearance, and I can find it. But the point is to see if the gap between the flywheel and pressure plate is uniform at 8 different places around the circumference. This will also ensure the PP can in fact provide the full gap to allow the disc (once installed) to spin completely free from contacting both flywheel and pressure plate surfaces during clutch engagement.

Larry

EDIT: TO Bearing is BCA # 614018 = GM #15680264 = Delco #CT24AG.

I believe Lars stated that 0.500 to 0.580 inches TO bearing depressed should provide 0.050 inches total clearance for the clutch disc. The 0.500 inch is desired, and the 0.580 inch represents a worst case. Lars entire tech presentation on this subject is in the archives.

Last edited by Powershift; 04-13-2019 at 07:34 PM.
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Old 04-13-2019, 08:25 PM
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Thanks, Larry. I plan to check the flywheel flatness as mounted on the engine. Also, I see the previous posts, and Lars recommends the pressure plate and clutch system be verified to produce the full .050 of clutch disengagement at just .400 of throwout bearing movement. I will need to find somewhere with an appropriate shop press to perform this measurement and do so at several points around the perimeter.
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Old 04-13-2019, 08:48 PM
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This can be a nightmare anymore because of so many defective parts . Check out my recent thread last fall . It turned out to be a defective new flywheel "AND" pressure plate and were both higher priced brand names .

Last edited by bj1k; 04-13-2019 at 08:49 PM.
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Old 04-14-2019, 07:23 AM
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DansYellow66
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The clutch and pressure plate surfaces don't look all that bad but it does appear that maybe there is uneven contact radially. In other words the pictures appear to show more wear in the outer half than the middle half. But the pictures may be deceiving and that may not be the case in direct visual examination. But I don't see any heavily burned areas that generally are seen with bad runout on the flywheel surface or a pressure plate disc that is engaging on one side before the other. I would lay a high quality straight edge across the pressure plate surface and see if it is flat or shows some slight gap towards the inside edge. I don't know what clutch that is but with the effort to R/R a Corvette transmission and clutch I would probably bite the bullet and put a new one in. If the flywheel checks out flat with minimal runout it may not even need to be re-surfaced as the previous surface machining pattern is still clearly present. But if you have a quality machine shop around that does flywheel surfacing I would probably go ahead and have it done as a precaution.

If you decide to investigate the pressure plate further I would dig out LARS post from years ago on testing pressure plate engagement in a hydraulic press. With the pressure plate in full release (.050 gap between pressure plate and disc) I would confirm thee gap is reasonably consistent all around the circumference with feeler gages. Basically what Larry covered above but LARS thread goes into more detail

https://www.corvetteforum.com/forums...vel-range.html
https://www.corvetteforum.com/forums...-c1-vette.html

I would check all the motor mounts also to be sure they are tight and in good condition.

Good luck

Last edited by DansYellow66; 04-14-2019 at 07:33 AM.
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Old 04-14-2019, 07:50 AM
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Tampa Jerry
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I agree with the above. While it's out, consider having the assembly balances by a competent machine shop. Jerry
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Old 04-14-2019, 10:54 AM
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Frankie the Fink
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Was everything dry when you got it apart? It only takes an eye dropper worth of grease to cause problems.
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Old 04-14-2019, 01:02 PM
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Thanks for all of your responses so far. I have some items to check in the near future.

And yes, Frankie, everything was dry inside the clutch area when I pulled it apart.

Thanks,
Dave
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Old 04-15-2019, 10:58 AM
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Default Pressure plate diagnosis

OK. I made some measurements on the old pressure plate this morning. The face of the clamping surface is "cone shaped." The inner radius is .006 to .008" shallower than the outer radius. Secondly, the clutch diaphragm fingers are not in an even plane. From high to low, the height varies .086". (I am thinking of purchasing a McLeod Street Pro clutch, and their tech support stated that any finger height deviation above .050" is unacceptable).
I am pretty sure this issue with the fingers was the cause of the clutch pedal vibration/noise when the clutch was engaged and also the clutch chatter issue. See illustrations below...

I still have to measure the flywheel flatness. I plan to get to that in a couple of days.

Pressure Plate inspection...






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Old 04-15-2019, 01:48 PM
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DansYellow66
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I think you have pretty much diagnosed the issue. One suggestion however, when you receive your new parts give them a good check over also to make sure they are not substandard also. I've bought new stuff and it was no good, as have a number of other posters on here.
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Old 04-15-2019, 02:07 PM
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Yeah - I think you've definitely tracked the issue down...annoying problem for sure..
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Old 04-15-2019, 02:51 PM
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Thank you for excellent documentation. I have wery same problem and would like to know what clutch are you going to bay?
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Old 04-15-2019, 03:04 PM
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Originally Posted by DansYellow66 View Post
I think you have pretty much diagnosed the issue. One suggestion however, when you receive your new parts give them a good check over also to make sure they are not substandard also. I've bought new stuff and it was no good, as have a number of other posters on here.
Believe me, I plan to measure as many features as possible before bolting things back up!
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Old 04-15-2019, 03:07 PM
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Originally Posted by bowtie racing View Post
Thank you for excellent documentation. I have wery same problem and would like to know what clutch are you going to bay?
I am not going to jump the gun and assume that this is the entire root cause. I still need to check flywheel flatness.
I plan to purchase a McLeod Street Pro clutch kit.
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Old 04-16-2019, 12:26 AM
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Originally Posted by CrystalRedZ View Post
I am not going to jump the gun and assume that this is the entire root cause. I still need to check flywheel flatness.
I plan to purchase a McLeod Street Pro clutch kit.
That's what I put in my 67 a few years ago. I cured my clutch pedal travel problem but I still have a little chatter in reverse. I've come down to believe its the material that the clutch is made of, maybe ceramic.
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Old 04-16-2019, 08:04 AM
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DansYellow66
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Originally Posted by Desert Nomad View Post
That's what I put in my 67 a few years ago. I cured my clutch pedal travel problem but I still have a little chatter in reverse. I've come down to believe its the material that the clutch is made of, maybe ceramic.
What type of disc did you use - dual friction by any chance (organic one side and ceramic the other? I've noticed a few of us with McLeod clutches and dual friction discs have reported a bit of chatter at times in reverse. Don't recall that with the organic disc.

I sort of question that we really need a dual friction clutch in our cars even with close to 500 HP as long as original size-equivalent tires are being used and the car isn't being used for racing. An organic clutch held up in these cars even under some heavy use conditions for years with no problem. But McLeod likes to recommend them, especially for the 427 cars.

Last edited by DansYellow66; 04-16-2019 at 08:17 AM.
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Old 04-16-2019, 09:29 AM
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Originally Posted by CrystalRedZ View Post
I am not going to jump the gun and assume that this is the entire root cause. I still need to check flywheel flatness.
I plan to purchase a McLeod Street Pro clutch kit.
Can you ID the flywheel and clutch manufacturer? If the flywheel is GM it will have a casting number on the front side. Report any ID info you find and maybe we can figure out what you have. All GM clutches and flywheels have a stamped X, which should be aligned as close as possible to get the best flywheel/clutch balance.

Check that the flywheel and crankshaft mounting surfaces are clean and free of any burrs, which could cause runnout.

Check that the clutch cover is properly torqued to the pressure plate. This could be the cause of the uneven finger face. If the flywheel is GM I would recommend having it surfaced by a machine shop rather than purchasing aftermarket, and those who have replaced the clutch with an OE replacement Luk have reported satisfactory results as long as the flywheel face was true.

Duke

Last edited by SWCDuke; 04-16-2019 at 09:36 AM.
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Old 04-16-2019, 10:20 AM
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Originally Posted by CrystalRedZ View Post
I am not going to jump the gun and assume that this is the entire root cause. I still need to check flywheel flatness.
I plan to purchase a McLeod Street Pro clutch kit.
I think you did a excellent job looking at all the different stack up things that could cause the clutch chatter. I remember checking my GM flywheel at .004 runout and installing an all stock clutch on my 63 car, it works normal.

Seems like these conversations are happening more around here with all the expensive off sure parts, you have to check everything, FWIW I would also check the total runout after you install the flywheel on the crankshaft.
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Old 04-16-2019, 10:26 AM
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http://www.powerparts.it/valeo_clutches.htm Large international company with a large following in Europe. They are moving into the American Market as well. They have a very large and complete catalog with excellent troubleshooting and pics if you just Google the name. I thought it was a bit too much to post here, but was a good read.

Larry
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Old 04-16-2019, 10:38 AM
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Originally Posted by SWCDuke View Post
Can you ID the flywheel and clutch manufacturer? If the flywheel is GM it will have a casting number on the front side. Report any ID info you find and maybe we can figure out what you have. All GM clutches and flywheels have a stamped X, which should be aligned as close as possible to get the best flywheel/clutch balance.

Check that the flywheel and crankshaft mounting surfaces are clean and free of any burrs, which could cause runnout.

Check that the clutch cover is properly torqued to the pressure plate. This could be the cause of the uneven finger face. If the flywheel is GM I would recommend having it surfaced by a machine shop rather than purchasing aftermarket, and those who have replaced the clutch with an OE replacement Luk have reported satisfactory results as long as the flywheel face was true.

Duke
Duke brings up a good point about torquing and tightening. When installing a pressure plate, one needs to first finger tighten all the bolts. Then tighten in a star type torque pattern (like wheels) tightening only about 1/4 to 1/2 turn each round until final torque is reached. Takes awhile to do this.

I have never seen one that was tightened incorrectly and failed............but then I have always done my own work and never had an issue. Perhaps the install for the OP car was done incorrectly and caused some of the problem.

Regardless, every step these days needs to be checked, rechecked, and verified.

In previous threads we stated flywheel run-out for flatness should be less than 0.003 inches. Perhaps the 0.004 inch barb mentioned is also okay as a guide, but one can see that we need to keep it very low to get success. If it was over 0.004 I would question the final product, and look for something else, or refinish and then recheck. FWIW.

Larry

Last edited by Powershift; 04-16-2019 at 10:41 AM.
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