69 Barracuda Clutch Shake Help Needed.

[jbc426]

I should have specified. What I measured about 5 degrees negative was the drive shaft angle toward the pinion as it was still hooked to the yoke. I unhooked the drive shaft from the rear pinion and rotated the pinion yoke around so I could attach the magnetic angle finder to it. I got 2 degrees positive that way. I'm going to do the same thing with my 71 Cuda and make sure I see a difference. That car has an 8 3/4 with 4 speed, and if I'm doing this right, should be negative at that spot. The 71 does not chatter. Just comparing.

So , with the car up on jack stands located under the rear end. You measured 2 degrees positive for the rear end pinion centerline? (pointing upward towards motor).

What is the angle of the transmission centerline? You will need to know this to determine the relation of that angle to your pinion angle. Under full throttle, they should be offset, but parallel. At rest, the pinion angle should be pointing down a few degrees in relation to the transmission centerline angle to allow for the upward rotation of the rear end under power.

 

[TimS]

So , with the car up on jack stands located under the rear end. You measured 2 degrees positive for the rear end pinion centerline? (pointing upward towards motor).

What is the angle of the transmission centerline? You will need to know this to determine the relation of that angle to your pinion angle. Under full throttle, they should be offset, but parallel. At rest, the pinion angle should be pointing down a few degrees in relation to the transmission centerline angle to allow for the upward rotation of the rear end under power.

No that 2 degrees positive was measured with the tires on the ground at ride height. I did get a more positive readying with the car on stands. Not a true one I don't think. Were would I set the angle finder, tail of the tranny or at the drive shaft toward the tranny?

 

[AJ/FormS]

IMO,only two sources could be your issue; the clutch or a dancing pinion angle.
A pinion angle by itself and not dancing,has to be pretty lousy to be noticed on take-off. All other sources of vibration would be continuous. The only source for a changing pinion angle is the rear springs.I would get someone to eyeball them while you do the E-brake test .

 

[TimS]

IMO,only two sources could be your issue; the clutch or a dancing pinion angle.
A pinion angle by itself and not dancing,has to be pretty lousy to be noticed on take-off. All other sources of vibration would be continuous. The only source for a changing pinion angle is the rear springs.I would get someone to eyeball them while you do the E-brake test .

I will do that E Brake test as you suggested. My plan was to pinpoint the angle issue and if it is there to just replace the springs. I may try wedges at the perches just as a trial for an ease out take off. I suspect that the bad springs is a root cause of the bad pinion angle.

 

[Inertia]

Does your diff have a snubber on it. If so, measure distance between snubber and vehicle floor, cut 2x4 a little longer. Jack up rear, place 2x4 between floor and diff snubber, lower jack trapping the 2x4, thus stabilizing diff , drive it.
All diff motion has been cancelled and shake will likely still be there.

I would also chain down the driver's side of the engine to limit engine lift, and subsequent clutch linkage motion.

RE-Resurface flywheel. jmo

 

[AJ/FormS]

I would also chain down the driver's side of the engine to limit engine lift, and subsequent clutch linkage motion.

Good call!
But if it was thaaat loose, I expect it would really bang during the shift, and any time the power is shifted from on to off,as the engine falls down.

 

[TimS]

Good call!
But if it was thaaat loose, I expect it would really bang during the shift, and any time the power is shifted from on to off,as the engine falls down.

Correct. I have had a motor mount issue in past years and you would feel that on a 1st to 2nd shift as well. At least I did in the past.

 

[TimS]

Does your diff have a snubber on it. If so, measure distance between snubber and vehicle floor, cut 2x4 a little longer. Jack up rear, place 2x4 between floor and diff snubber, lower jack trapping the 2x4, thus stabilizing diff , drive it.
All diff motion has been cancelled and shake will likely still be there.

I would also chain down the driver's side of the engine to limit engine lift, and subsequent clutch linkage motion.

RE-Resurface flywheel. jmo

Hey thanks for the trick. Did just that with the 2X4. No shake and I can even turn the tires a bit. I believe that seals the deal on the weak springs or too positive of a pinion angle. I will say I did my pinion angle checking on my 71 Cuda I've owned for 22 years that has no shake. That car is 1-2 degrees negative.

 

[TimS]

Hey thanks for the trick. Did just that with the 2X4. No shake and I can even turn the tires a bit. I believe that seals the deal on the weak springs or too positive of a pinion angle. I will say I did my pinion angle checking on my 71 Cuda I've owned for 22 years that has no shake. That car is 1-2 degrees negative.

I'm thinking of putting an adjustable pinion snubber on it till I get my springs.

 

[Inertia]

Hey thanks for the trick. Did just that with the 2X4. No shake and I can even turn the tires a bit. I believe that seals the deal on the weak springs or too positive of a pinion angle.

I'm glad it worked out for you..

cheers..

 

[1969383S]

I'm thinking of putting an adjustable pinion snubber on it till I get my springs.

Glad you think you got it!

So you think the springs are bad? You started the post by saying "All is original". Even if the springs are weak the pinion angle should not have changed drastically. You even have talked about referencing other vehicles for the angle. I can understand that if the springs are junk you could have these issues. Seems you could have easily determined there was an issue long ago just looking at the springs and inner liners, are they still there? Mine still has the "Original rebuilt springs" and never had pinion angle issues before or after rebuild. Hope your not throughing more good money for bad at it.

 

[TimS]

Glad you think you got it!

So you think the springs are bad? You started the post by saying "All is original". Even if the springs are weak the pinion angle should not have changed drastically. You even have talked about referencing other vehicles for the angle. I can understand that if the springs are junk you could have these issues. Seems you could have easily determined there was an issue long ago just looking at the springs and inner liners, are they still there? Mine still has the "Original rebuilt springs" and never had pinion angle issues before or after rebuild. Hope your not throughing more good money for bad at it.

What are you referencing when you say inner liners? Springs in stance and appearance look no different than my 71 or 72 Cudas. In 40 years of working with and restoring lots of 68-74 Mopars I have never had a spring issue that effected the cars performance. Juts been lucky to this point I guess. However I can't deny the fact that when I put that 2X4 between the snubber and the floor to prevent any rear positive load change, car did not shake. This car also shook with the old clutch.

 

[1969383S]

The plastic pieces between the springs
Like these. Our cars have an extra leaf the kits do not cover. I had to order 2 extra of the black plastic inter liners when I refurbished them. When I rebuilt mine the springs were much taller if that makes sense. All of mine were mostly disenergrated after years of drag racing. Again my pinion angle was never an issue. Seems to me only changing the perches would effect the angle much!

 

[TimS]

The plastic pieces between the springs
Like these. Our cars have an extra leaf the kits do not cover. I had to order 2 extra of the black plastic inter liners when I refurbished them. When I rebuilt mine the springs were much taller if that makes sense. All of mine were mostly disenergrated after years of drag racing. Again my pinion angle was never an issue. Seems to me only changing the perches would effect the angle much!

View attachment 1714934585

I'll take a look at the liners. I put an adjustable snubber on it and put the end very close to the floor. It still shakes a bit but isn't violent as with the stock snubber that's about 4 inches away from the floor. It does make sense that the liners would make it taller. I'm just thinking of buying a set of the super stock springs so I can increase that right height in the rear and get the stock shackles back on it. Though I only added an inch to the rear with the aftermarket ones.


I'll check out the inner liners. I did put an adjustable pinion snubber on and got the rubber nose very close to the floor. Unlike when I wedged the 2X4 I get some shake that way, just not violent as with the stock snubber.

 

[1969383S]

I'll take a look at the liners. I put an adjustable snubber on it and put the end very close to the floor. It still shakes a bit but isn't violent as with the stock snubber that's about 4 inches away from the floor. It does make sense that the liners would make it taller. I'm just thinking of buying a set of the super stock springs so I can increase that right height in the rear and get the stock shackles back on it. Though I only added an inch to the rear with the aftermarket ones.


I'll check out the inner liners. I did put an adjustable pinion snubber on and got the rubber nose very close to the floor. Unlike when I wedged the 2X4 I get some shake that way, just not violent as with the stock snubber.

Sounds like a good plan!

Save the original springs if you have space though! Having all the clamps front and rear makes a difference as well and good through pins. I had taken the rear clamps off mine with slapper bars installed back in the racing days!

 

[Killer6]

Even after I've gotten this one warmed up, it still chatters violently. I went as far as putting the car in 1st gear, setting the mercy brake and easing out the clutch, throttling the motor to heat up the clutch.

I wasn't suggesting your clutch had to be cold or damp, I simply stated even some stock clutches behave that way under certain conditions. The finish on the flywheel & type of lining/hub are what I was addressing in your case. If mounts-etc. all check out, I have installed truck & Hipo discs that chattered no matter what you did, some racing clutches are either in or out,there's no "sliding" 'em.

 

[TimS]

I wasn't suggesting your clutch had to be cold or damp, I simply stated even some stock clutches behave that way under certain conditions. The finish on the flywheel & type of lining/hub are what I was addressing in your case. If mounts-etc. all check out, I have installed truck & Hipo discs that chattered no matter what you did, some racing clutches are either in or out,there's no "sliding" 'em.

I see. I did have someone stand behind the car and watch the rear. The springs really seemed to move allot with torque applied. Kind of an up and down motion. I'm even wondering now, could it be possible I have a perch weld broken which allowed the pinion to go a bit positive. I also noticed that when I put the the adjustable snubber on and dumped the clutch real hard just to see what kind of rubber trail I could leave, I got allot on the LH side, basically till as long as I stayed in it. Not much on the right. I know that could be a rear gear issue. I do have a sure grip rear with 3.23's. Wondering if that's a clue.

 

[1969383S]

Don't forget to address the shocks as well. If you go with super stock springs or extended shackles you need a longer shock than stock. I suggest the MOPAR long shocks available from JEGS or others.

 

[TimS]

Don't forget to address the shocks as well. If you go with super stock springs or extended shackles you need a longer shock than stock. I suggest the MOPAR long shocks available from JEGS or others.

Thanks for the heads up on the shocks. I didn't know that. I put the 2 degree angle shims in. Shake is less but still a bit present. I'm wondering if I should go 4 degree shims if that would take the shake out altogether.

 

[TimS]

Well just to update on this shake situation, I'm still shaking at standing start take off. My efforts had been placed at the rear of the car thus far. I have:

Added 2 then 4 degrees to my pinion angle. Ensured there are no broken welds at the perches.
Fabricated and installed bar clamps on the front section of the leaf springs. The springs already had 2 stock clamps.
Added an adjustable pinion snubber and have that about 1/2 inch form the floor.
Removed my aftermarket rear shackles and reinstalled the stock shackles.
Installed new shocks (old ones were junk) and added springs over those to raise the car rear a bit.
Removed inspection cover and made sure the new pressure plate fingers make uniform contact with the new throw out bearing. Also checked it's operation which appeared very smooth as the clutch is engaged and disengaged.
Checked all motor mounts to make sure they are not broken or loose.
Checked the linkage again for free movement.
Car has a non stock rear sway bar so I unhooked that. Thanks members for clearing that up for me. I thought it was stock.

My next checked was going to be on the rear carrier itself. Before pulling I called DR Diff in Montana. He felt based on my shake only at take off the issue was no where in the rear end area including the carrier.

In my previous posts I mentioned I was going to buy a set of springs. 1969383S, I believe your right on the throwing good money for bad at this. I believe I would have, buying new springs. For now I've decided to ditch that and pull the clutch assembly back out. Now that I've driven the car a bit I suspect a check of the flywheel would be in order.

 

[nm9stheham]

Sounds like a clutch release chatter interacting with the natural resonant frequency of the spring and axle wrap. That is always there unless some positive control is added to stop it.

BTW, what DO you have for motor and trans mounts? They are all part of the drivetrain wrap up.

I had the same type of thing in a plain old /6 early Dart. A different new clutch solved it. Nothing could clearly be seen wrong on the other one, but it chattered just the same. Could be a lot of things in the clutch area.

 

[1969383S]

Lets go back to the clutch.

You had an issue with the install that may seem minor, but could have really effected the hat and disc when it made contact with the bell housing. Think about that and how it may have upset the springs on the clutch facing. Did one break? There may be more info you have not shared that may help one of us lead you to the real issue you search to find.

 

[TimS]

Lets go back to the clutch.

You had an issue with the install that may seem minor, but could have really effected the hat and disc when it made contact with the bell housing. Think about that and how it may have upset the springs on the clutch facing. Did one break? There may be more info you have not shared that may help one of us lead you to the real issue you search to find.

I would agree. Even though I posed the question to Wayne Brewer and he didn't feel it would have an impact, that pressure plate housing was hitting the bell housing while running. I had a well known shop in town do the swap for me. I mentioned I thought they did make a mistake by not checking the clearance before they stuck all that together and started the car. Should have at least rotated everything around a couple of times before buttoning up the inspection cover. I've got a picture of that around here somewhere that I sent to Wayne. I will post it as soon as I find it.

 

[TimS]

I would agree. Even though I posed the question to Wayne Brewer and he didn't feel it would have an impact, that pressure plate housing was hitting the bell housing while running. I had a well known shop in town do the swap for me. I mentioned I thought they did make a mistake by not checking the clearance before they stuck all that together and started the car. Should have at least rotated everything around a couple of times before buttoning up the inspection cover. I've got a picture of that around here somewhere that I sent to Wayne. I will post it as soon as I find it.

Here a couple of shots of the nick in the pressure plate housing. This happened in 4 or 5 places I believe.

 

[Inertia]

I maintain its the clutch/flywheel,.. re-remachine the flywheel, or try a different one.

It's really painful watching someone go thru something you been thru a few dozen times cuz the customer was too cheap to machine the flywheel, and then had to re-do the job in order to machine the flywheel true, to correct the "shudder".

I realize you had it resurfaced, but machine shops make mistakes too, trust me, I've come across lotsa incorrect machine work. One piece of grit on a mounting surface ..

And then there's the clutch interference issue.. to me that's a flag there's something outta proportion there, and be more curious about that.

IMHO you're chasing your tail trying to cure symptoms, instead of the fundamental cause, power is being transffered to the drivetrain in an inconsistant manner.

The spring motion is a visual representation of the power being received. Smooth power transfer, the spring would remain evenly torqued.

jmo

good luck..