# Clutch chatter



## Dsetzer49 (Jul 25, 2020)

I recently installed a new clutch pressure plate throw out bearing and pilot bearing in my 1968 GTO. It has the original Muncie m-20. I used an economical (cheap) kit from rock auto. I did not have the flywheel machined when it was apart and I believe it to be original 200k miles. I now get chatter in first gear on occasion and in reverse. I’d machining the flywheel the answer or will it go away? Should I have replaced the flywheel with that many miles on it?


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## Old Man Taylor (May 9, 2011)

Chatter doesn't usually go away. The original flywheels are cast iron, so it would not be a bad idea to replace it with that many miles on it. As a band aid you could try slipping the clutch a lot under power, but that also risks making it worse. I would just leave it as it is until you get enough money to do it right.


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## NOS Only (Nov 14, 2017)

First mistake was to not have the flywheel resurfaced. Second was "cheap" parts. Because for those two it will cost you twice as much to do it right the second time as the new parts are damaged and there is no repair for those.

Go buy a good clutch setup and have the flywheel machined.

Think of a clutch setup like a disc or drum brake setup because they are basically the same. You wouldn't put new pads or shoes on without machining the surface of the rotor or drum.


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## Dsetzer49 (Jul 25, 2020)

Old Man Taylor said:


> Chatter doesn't usually go away. The original flywheels are cast iron, so it would not be a bad idea to replace it with that many miles on it. As a band aid you could try slipping the clutch a lot under power, but that also risks making it worse. I would just leave it as it is until you get enough money to do it right.


Thank you for the info. I will probably live with it for a while. It seems to happen only pulling in and out of the garage. I am working on interior now and it will run and drive pretty well for now. I do think that when I get on it and the motor starts pulling hard the clutch is slipping. It just feels like when it gets to about 3000 rpm the torque and traction are more than the clutch can handle. I drove it with the old clutch but it had 25 year old tires on it that would not bite at all.


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## Dsetzer49 (Jul 25, 2020)

NOS Only said:


> First mistake was to not have the flywheel resurfaced. Second was "cheap" parts. Because for those two it will cost you twice as much to do it right the second time as the new parts are damaged and there is no repair for those.
> 
> Go buy a good clutch setup and have the flywheel machined.
> 
> Think of a clutch setup like a disc or drum brake setup because they are basically the same. You wouldn't put new pads or shoes on without machining the surface of the rotor or drum.


Thanks for help. The parts that I bought from rock auto were hit and miss, none of the parts from Summit racing fit my applications. All of the parts from Ames have been spot on.


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## Jared (Apr 19, 2013)

When you have the trans out again, double check the bearing retainer on the front of the transmission for wear. I'm not sure if it's an issue on Pontiacs but I know the stick shift Oldsmobile's would develop a jagged groove along the bottom where the throw out bearing rides. Also check the pilot bushing/bearing for wear. Both those parts are cheap and easy to replace while you have the car apart. I have a Ram clutch kit that was on my car before the engine blew. I was pretty happy with it and it definitely would not slip on a stock output GTO.


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## PontiacJim (Dec 29, 2012)

Old Man Taylor said:


> Chatter doesn't usually go away. The original flywheels are cast iron, so it would not be a bad idea to replace it with that many miles on it. As a band aid you could try slipping the clutch a lot under power, but that also risks making it worse. I would just leave it as it is until you get enough money to do it right.


With that many miles, as has been pointed out above by *OMT*, the flywheel should have been removed and surfaced by a machine shop. While out it can be inspected for any bad cracks (they usually have heat cracks which is normal), worn ring gear, and if it has ever been machined in the past - like rotors/drums, the flywheel has a minimal thickness before it becomes too weak and is not safe anymore. Your flywheel surface could have uneven wear, scoring, or dips/valleys and be contributing to the chatter issue.


The stock flywheel is cast and is fine for most stock or mild build applications. But it is always better to step up to an aftermarket steel flywheel as they are stronger, and of course fresh machined surface and new ring gear. The aftermarket steel flywheels are drilled for both the factory 10.5" pressure plate and 11" pressure plate bolt pattern. The 11" gives you more surface area for grip when using the larger size, and you can still get a low pedal pressure. With the aftermarket flywheel you want to make sure you get/use the correct flywheel bolts as some of the replacement sets will say they fit, but the heads are too tall and the center springs on the clutch disc will strike them. Not sure if the factory flywheel bolts work on these aftermarket flywheels because I went with new replacements and learned the lesson on which bolts you don't want to use. LOL The aftermarket flywheels are also "neutral balanced" and can work as is in most cases, but I have read that it is best to have the new flywheel balanced to match your factory take-off flywheel. Again, a good engine machine shop can do this or send both flywheels out and the replacement balanced to match the factory flywheel.

I have had new quality clutch set-ups chatter. It can depend on the clutch face material in some instances as there is a variety of compounds used depending on application. Some clutch discs use a solid hub versus a sprung hub - which is important for a street car. Sprung hubs really help make a clutch streetable to a large degree, meaning reducing chatter and jerking when letting the clutch out. Sprung hubs reduce the stress on the drivetrain that is caused by crank harmonic twisting. Solid hub discs can be difficult to drive on the street and exhibit extreme on-off engagement characteristics making them hard to drive smoothly, and exhibit chattering upon engagement. Some clutches use a "Marcel spring" between the 2 halves of the clutch disc. This is a wavy flat spring that is bonded to the friction material, and then riveted to the disc itself. You can see it when looking at a clutch disc on its edge. The marcel acts like a cushion, smoothing out the final engagement of the friction material by allowing the clamping forces to build up a little slower. When the clutch is fully engaged, the marcel smashes flat and has no effect. Not all discs will have a marcel spring. So some of these features allow for a smoother take-off and minimize chatter, while other features you would not want with regards to a high performance or race car.

Using a stiff rear axle ratio, like when swapping from an automatic to a 4-speed and using the automatic's "highway gearing" takes a lot of clutch to get the car rolling from a stop and this is where I have experienced chatter if you don't bring the RPM's up enough to really slip the disc more than you would like. So raising the RPM's and slipping the clutch more to get rolling may minimize the chatter, but wear the clutch more.

I used to purchase the NAPA remanufactured pressure plate/clutch set-up when I was young and had a 1967 GTO. They were inexpensive and all I could afford. I had swapped the 3.90 rear end with an automatic rear axle of unknown gearing, but most likely 3.08's or 2.90's coming out of another GTO with a 2-speed auto. I had a close ratio 4-speed which made taking off worse, so I had to slip the clutch to get rolling, and when I would do a hard power shift, the clutch would slip a bit as well. The remanufactured parts just were not up to the task with regrads to the clamping forces needed to keep the clutch from slipping due to the high torque of the 400CI and those highway gears in the rear. At that time, I did not know all this. So a remanufactured kit lasted about 3 months before the clutch started slipping and no further clutch adjustments could be made. It was then time to put in another kit. After doing 3 of these changes, when I was ready for number 4, I put a TH-400 automatic I had laying around into the car and that ended the problem and healed my wallet.

So the bottom line is that you can get an inexpensive clutch set-up to save money, and it may work in most instances, but with the torque the 400CI has and depending on your transmission's first gear and the rear axle gearing, the inexpensive clutch kits may not have enough clamping force to prevent the clutch from slipping even if you have everything perfectly adjusted. The other side of the coin is that you don't want a pressure plate that has the clamping force of a 10-ton press in your street car as it will take 2 left legs to push it in and your left arm/hand to keep your knee locked up when the pedal is pushed to the floor. Used one of these set-ups in another car - that clutch never slipped, ever! LOL So you want to do the research and select a good set-up that provides a good clamping force on the clutch, but is not killer to push in the clutch pedal and have to hold it down when in stop/go traffic.


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## JohnStauver (Nov 29, 2020)

Dsetzer49 said:


> I recently installed a new clutch pressure plate throw out bearing and pilot bearing in my 1968 GTO. It has the original Muncie m-20. I used an economical (cheap) kit from rock auto. I did not have the flywheel machined when it was apart and I believe it to be original 200k miles. I now get chatter in first gear on occasion and in reverse. I’d machining the flywheel the answer or will it go away? Should I have replaced the flywheel with that many miles on it?


On other thing to think about along with the other good posts is using a proper aligning tool for the disc and gradually tightening the pressure plate. If your trans didn't slip into the clutch easily then it's possible to distort the hub on the clutch disc.


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## 64since65 (Dec 11, 2019)

PontiacJim said:


> ....So you want to do the research and select a good set-up that provides a good clamping force on the clutch, but is not killer to push in the clutch pedal and have to hold it down when in stop/go traffic.


So any advice on how to do that research? I've been looking at catalogues and they just say "it fits". (OK, some say they handle higher torque but never seem to give any numbers.) I haven't seen any info about torque capacity, clamping force, or bearing loads (pedal force) anywhere. I used to know some guys at LUK that I could have asked (probably even got a free clutch) but they retired a few years before I did.


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## O52 (Jan 27, 2019)

I bought a LUK clutch for my 68. Haven't heard anything bad and lots of good things about them. Seem to work well with stock or mild builds.


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## Old Man Taylor (May 9, 2011)

I’ve stuck with two clutches: McLeod and CenterForce DF.


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## PontiacJim (Dec 29, 2012)

64since65 said:


> So any advice on how to do that research? I've been looking at catalogues and they just say "it fits". (OK, some say they handle higher torque but never seem to give any numbers.) I haven't seen any info about torque capacity, clamping force, or bearing loads (pedal force) anywhere. I used to know some guys at LUK that I could have asked (probably even got a free clutch) but they retired a few years before I did.



Most will include HP levels. Many are for the 11" set-up, so select to match your flywheel if you plan on using your factory 10.5" You want to make sure you get the correct spline count on the clutch disc/hub to match your trans input shaft - which you probably already know about.

Everyone will have a personal opinion, so it makes it tougher to choose what you think is best. Generally, any nam brand manufacturer/supplier should do the trick. I have used McLeod. Just make sure you get the correct/matching length throwout bearing for the application. McLeod sent me the wrong one in one kit I ordered - it was too short and my pedal went near to the floor and it would not disengage the clutch. The correct longer length solved the issue, but had to pull the trans out all over again to replace it.


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## RMTZ67 (Mar 12, 2011)

PontiacJim said:


> Most will include HP levels. Many are for the 11" set-up, so select to match your flywheel if you plan on using your factory 10.5" You want to make sure you get the correct spline count on the clutch disc/hub to match your trans input shaft - which you probably already know about.
> 
> Everyone will have a personal opinion, so it makes it tougher to choose what you think is best. Generally, any nam brand manufacturer/supplier should do the trick. I have used McLeod. Just make sure you get the correct/matching length throwout bearing for the application. McLeod sent me the wrong one in one kit I ordered - it was too short and my pedal went near to the floor and it would not disengage the clutch. The correct longer length solved the issue, but had to pull the trans out all over again to replace it.


Hey Jim I noticed you mention the longer throwout bearing when it comes to clutches. Mine had the short one when I got the car and have installed two short ones since with no issues. Question is...I wonder what the difference is? 3 speed Dearborn? Fork difference?


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## Old Man Taylor (May 9, 2011)

The best clutch I have ever used was the Corvette L88. It was discontinued a long time ago. I still have a couple of coarse splined disks, but I no longer have any pressure plates. They were 10 3/8" (stock) clutches.


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## Old Man Taylor (May 9, 2011)

In my experience the high cone diaphragm pressure plates work best in Pontiacs. That's the type of clutch that came stock, but the stock ones weren't good on higher horsepower engines. I've tried the 3 finger clutches (called Long clutches) with poor success. I tried running a Scheifer in the late 60's. My problem at the time was how the car launched at the track. I had hoped that I would be able to slip a 3 finger clutch and get it to hook up better. However, when I slipped the clutch and gave it power, it wouldn't engage. The clutch just slipped more. Plus it required an incredible amount of pedal effort. I was driving into the work parking lot, depressed the clutch, and the pedal went to the floor. It had broken the bracket that is welded onto the frame. I had a thicker bracket welded back on and changed back to a diaphragm clutch as soon as I had the time and money.


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## PontiacJim (Dec 29, 2012)

RMTZ67 said:


> Hey Jim I noticed you mention the longer throwout bearing when it comes to clutches. Mine had the short one when I got the car and have installed two short ones since with no issues. Question is...I wonder what the difference is? 3 speed Dearborn? Fork difference?


Pic #1 & #2 - As *OMT* mentioned, it depends on what type of pressure plate you use and how the "fingers" are orientated. I have seen the diaphragm type having both a flat and a raised finger arrangement. In this case, the raised height of the fingers could dictate the short/long throw out bearing length. The height of the pressure plate "hat" can also dictate the throw out bearing needed.

Pic # 3 - The Long style is a 3-finger pressure plate and has the narrow fingers and usually has weights fitted to their ends so the faster the plate spins, the more clamping force it applies to the disc - used for racing and the weights can be changed. This style is a Ford design.

Pic #4 - The Borg & Beck style is also a 3-finger pressure plate and can be identified by looking at the width of the clutch fingers, which is about one inch. The pressure plate applies clamping force to the disc using coil springs similar to a valve spring. By combining these springs at a specific installed height, different pressures can be attained for the pressure plate. These are generally used on higher HP cars, either street or race. Had one in one of my cars - 2-left legs were needed to hold it in if you got stuck in stop/go traffic. It has some pressure to it, but it won't slip. LOL

It can also depend on the shape of the clutch fork and I suppose the pivot ball found inside the bellhousing that the fork rides on. The McLeod kit I got that had the incorrect short throw out bearing, I was told it was a kit for a Chevy and not a Pontiac, that they used the short bearing. I don't know how true that was, I just went and got what I needed in throw out bearing length. This was not the first time I have run into this. It had happen a couple times in my youth, so apparently it still happens if you are not aware of it or have an old bearing to measure against. Easy to insert the wrong one when you are doing a swap from automatic to stick because you don't have that old one to go by. 

The throw out bearings also have different faces, ie differing diameters, flat, or rounded (self centering), and these have to match the pressure plate's finger type.


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## PontiacJim (Dec 29, 2012)

Old Man Taylor said:


> In my experience the high cone diaphragm pressure plates work best in Pontiacs. That's the type of clutch that came stock, but the stock ones weren't good on higher horsepower engines. I've tried the 3 finger clutches (called Long clutches) with poor success. I tried running a Scheifer in the late 60's. My problem at the time was how the car launched at the track. I had hoped that I would be able to slip a 3 finger clutch and get it to hook up better. However, when I slipped the clutch and gave it power, it wouldn't engage. The clutch just slipped more. Plus it required an incredible amount of pedal effort. I was driving into the work parking lot, depressed the clutch, and the pedal went to the floor. It had broken the bracket that is welded onto the frame. I had a thicker bracket welded back on and changed back to a diaphragm clutch as soon as I had the time and money.


Not saying this applies, but some pressure plates have several small blocks between the fingers and "hat" and have to be removed before using. I believe the Borg & Beck I once used had these. Instructions generally make you aware of this, but as us guys go, who reads instructions? LOL


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