67 Barracuda Formula S 451 - clutch shatter

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CallMeAl

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Hello everyone,

I have read many many threads about clutch shatter problems - also the one which has recently discussed in this forum.
The problem is quite similar:

- Take off in 1st gear is nearly impossible - extreme shatter, as if the dash would like to jump out of the car.
- Take off in 2nd gear is possible
- Reverse no problem

Things done:

- resurfaced flywheel installed
- new Centerforce Dual Friction 10.5" 23-spline clutch - all mounted correctly - doublechecked
- Leaf springs were restored with new clamps - to make sure they are not the problem, we have changed to a set of new springs - no difference
- Torque strap on driver side installed
- Pinion angle checked - was 1 degree nose down - adjusted to 5 degree nose down - no difference
- Z-Bar bushings had some side play - with new bushings there´s no play left now
- tested with a range of clutch linkage play settings - no difference
- Clutch pedal Over-Center spring removed
- changed over to a different clutch fork which has a bit of a different angle
- Throwout bearing checked


All these tasks did not lead us to any usable result.

Then we have taken out the trans and changed the clutch back to a standard one (used but nearly no signs of use)
Checked the flywheel again - also with a dial indicator - runs absolutely even.

With the standard clutch, the shatter is not fully gone, but now it is at least possible to take off slowly. With higher rpm or harder launching, the shatter is still present.

I´m running out of ideas and hope that there´s something else left we have overlooked.

Here´s 2 videos which show how the leaf springs act due to the shatter:





And one showing the engine while under load:



It still looks like there´s some engine movement although it is held by a torque strap.

Any ideas appreciated - thanks in advance!
Lars
 
This might be a longshot but what about flywheel balance? BTW, nice Cuda! 65'
 
What leaf springs are those? They appear a little anorexic. Kudos to the person who's running along side of your car filming.
 
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A56 said:
What leaf springs are those? They appear a little anorexic. Kudos to the person who's running along side of your car filming.
Click to expand...

After changing to new ones, we went back to the original rebuilt ones - the Formula S has the heavy duty 6 leaf springs.

IMG_0937.JPG
 
Pinion angle? The pinion should be pointing down a few degrees. It looks like it's pointing up in your last photo.
 
CallMeAl said:
Original, which came with the 383 that was in the car.
Click to expand...

The flywheel is cast and over the years can develop a or multiple hard spots.
I bet if you put a good steel flywheel in it it would fix the problem.
 
In reality if it only chatters when in-gauging and you can leave the clutch out slow down till it almost stalls and take off it's not in the drive line it is in the clutch. You have changed everything but the flywheel and nothing fixes it, it has to be the flywheel.

Back in the day before disc brake we had to grind brake drums because the cutting bits would bounce over the hard spots and even after grinding they always came back shaking when trying to stop, the hard spots always come back.
 
What did the surfaces of the pressure plate and flywheel look like when you had it apart. I've had my share of clutch chatter problems over the years. It is frustrating.

A broken drivers side motor mount will induce chatter, but I read you have a torque strap installed. Can you tighten that so that there is no play in it and it completely stops the driver's side of the engine from lifting up at all? That could eliminate any up and down movement of the engine as the clutch is let out.

I've also had bad pressure plates that show three or more hot spots where it is not evenly applying pressure to the entire clutch surface, and that induced chatter. You did change that out too I believe, and it altered the dynamic of your chatter. Is that correct?

Another time, I had a bad Marcel spring which is a wave style spring located between the two faces of the clutch disk was flat. It compresses when clamped between the pressure plate and the flywheel.

As mentioned above, a heat damaged flywheel can have both soft and hard areas that have different coefficients of friction can induce it too.
 
Since you've gone through so much already, I take it you've indicated your bellhousing in.
How was the fit for the trans input shaft to the crank bushing?


Have you tried it with the sway bar disconnected?
 
brian6pac said:
In reality if it only chatters when in-gauging and you can leave the clutch out slow down till it almost stalls and take off it's not in the drive line it is in the clutch. You have changed everything but the flywheel and nothing fixes it, it has to be the flywheel.

Back in the day before disc brake we had to grind brake drums because the cutting bits would bounce over the hard spots and even after grinding they always came back shaking when trying to stop, the hard spots always come back.
Click to expand...

That´s worth trying - thanks for the hint - I have another flywheel with minimal signs of use - will have it balanced & resurfaced and test that one as one of the next steps.
 
jbc426 said:
What did the surfaces of the pressure plate and flywheel look like when you had it apart. I've had my share of clutch chatter problems over the years. It is frustrating.

A broken drivers side motor mount will induce chatter, but I read you have a torque strap installed. Can you tighten that so that there is no play in it and it completely stops the driver's side of the engine from lifting up at all? That could eliminate any up and down movement of the engine as the clutch is let out.

I've also had bad pressure plates that show three or more hot spots where it is not evenly applying pressure to the entire clutch surface, and that induced chatter. You did change that out too I believe, and it altered the dynamic of your chatter. Is that correct?

Another time, I had a bad Marcel spring which is a wave style spring located between the two faces of the clutch disk was flat. It compresses when clamped between the pressure plate and the flywheel.

As mentioned above, a heat damaged flywheel can have both soft and hard areas that have different coefficients of friction can induce it too.
Click to expand...

The surface of the clutch looked a bit burned at some spots and not 100% good - like some clutch friction material sticks out at some points - the pressure plate had some colored areas from heat. It was a brand new Centerforce clutch and we did not abuse it. But I think the chatter has put some stress at it.

The torque strap is very tight - but anyhow on the one video where you see the engine from below while being on the dyno, looks still to move as I just noticed.
So we´ll check the passenger side engine mount as well to minimize engine movement.

When we have changed the clutch, we also changed the pressure plate. The dynamic of the chatter has changed - lot less - but still there.
 
Daves69 said:
Since you've gone through so much already, I take it you've indicated your bellhousing in.
How was the fit for the trans input shaft to the crank bushing?


Have you tried it with the sway bar disconnected?
Click to expand...

Yes, bellhousing is dialed in to specs.
The input shaft to crank bushing fit has about 0.2 mm = 0,00787402 inch - not sure if that is ok. Bushing is brand new. Input shaft has same diameter on the bushing area as on the other areas.

We did not disconnect the sway bar yet - good idea - I think as the car tries to twist to the right, the sway bar changes the spring rate at acceleration. But it should work with sway bar in the end ....
 
CallMeAl said:
Yes, bellhousing is dialed in to specs.
The input shaft to crank bushing fit has about 0.2 mm = 0,00787402 inch - not sure if that is ok. Bushing is brand new. Input shaft has same diameter on the bushing area as on the other areas.

We did not disconnect the sway bar yet - good idea - I think as the car tries to twist to the right, the sway bar changes the spring rate at acceleration. But it should work with sway bar in the end ....
Click to expand...

Looking at the last picture the sway bar has a link missing, so it is some what disconnected
 
Finally we have solved the problem :)

Further things done were change of the 8.75 gears to 3.23 instead of I think it was 2.76 - the shatter was a bit less, but still there.
Then we have took of the clutch again and changed the flywheel for a new one and went back to the Centerforce clutch. Problem still there.

The last thing we did not change was the driver side engine mount, as there are very limited options on the market for big block A-body engine mounts, and we did not want to go for a Poly engine mount on the first go. And we thought the torque strap would eliminate all engine movement on the driver side - BUT before we went to the next steps, we have noticed when pushing the clutch pedal, that the engine moved a tiny bit to the front - that movement is not blocked by the torque strap, it only blocks the side-movement, but not back/forth.
So just to see if it could be related to the engine mounts, we have machined some aluminium blocks as solid engine mounts as a test.
And voilá - the problem has completely disappeared! No trace of chatter anymore.

The lesson learned, is that with a weak old driver side engine mount (even when having a torque strap), while engaging the clutch, the engine torque and take-off accelleration of the car pushes the engine to the rear on the driver side and slightly disengages the clutch again, the engine moves to the front, the clutch engages slightly and the loop goes on and on, resulting in the massive chatter.....

As no other options are available we have bought a set of Poly-Loc engine mounts from PST and installed them - still perfect - and with even less vibration than expected with poly mounts inside the car.
 
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Congratulations! I typically use the rubber motor mounts with a polyurethane transmission mount. Glad you finally figured it out, now go out and have some fun! 65'
 
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