Violent Take-Off Shudder

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So was this a new install or just a clutch change, because 5/8 is a HUGE move.

Everything is a new install. Motor and all. The conversion mounts do not place the engine at a perfect angle every time since the tolerance of these cars allowed for some errors. If the motor mounts are rotated ever so slightly, that can result in a large change at the tailshaft of the trans. I actually had to shim my motor up to clear some steering. To combat my issue, I am going to remove my motor shims and keep the 5/8" tail shaft shim. This puts me at a perfect coinciding angle with the pinion. Of course once all of that is done, I will add a degree or two to the pinion side and add some caltracs to help with axle rotation. I would keep the snubber, but I like caltracs more. Both work, one is easier for me to fit my lard *** in to adjust at the track. :lol:
 
I’d like to thank everyone for this thread, I’ve had a similar problem in my 340 dart but never thought to look at the trans joint angle. As one poster stated it should be the same as the pinion joint angle. I’ve been living with it thinking it was the clutch, I’m going to check the trans joint angle now!
 
I’d like to thank everyone for this thread, I’ve had a similar problem in my 340 dart but never thought to look at the trans joint angle. As one poster stated it should be the same as the pinion joint angle. I’ve been living with it thinking it was the clutch, I’m going to check the trans joint angle now!


No problem! Here is am image of what you want to look for. Bare in mind that the pinion angle needs to be the same as dive line angle UNDER LOAD. So 5-7 degrees lower is what MP Performance books say per RustyRatRod.

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Everything is a new install. Motor and all. The conversion mounts do not place the engine at a perfect angle every time since the tolerance of these cars allowed for some errors. If the motor mounts are rotated ever so slightly, that can result in a large change at the tailshaft of the trans. I actually had to shim my motor up to clear some steering. To combat my issue, I am going to remove my motor shims and keep the 5/8" tail shaft shim. This puts me at a perfect coinciding angle with the pinion. Of course once all of that is done, I will add a degree or two to the pinion side and add some caltracs to help with axle rotation. I would keep the snubber, but I like caltracs more. Both work, one is easier for me to fit my lard *** in to adjust at the track. :lol:


Ok, I ASSumed this was just a clutch swap. Now it makes more sense. And no one said pinion angle doesn’t matter.

I still wouldn’t use that clutch. It’s a parts breaker, especially if you put some bite to it.
 
This is correct Rusty. I will add to this. Though the spec is 5-7, this wouldn't have made much of a difference until I put my foot in it. That 5-7 degrees is for the allowance of axle wrap to avoid trashing your ujoints. I think if I would have stepped on it enough with only a 2.4 degrees of pinion angle delta, I would have exploded the ujoint or even worse, the chunk. One thing I do want to highlight from this is the 0 degree delta from the tailshaft to the driveshaft. This can actually be worse than having your pinion angle out of spec. Why? I am still trying to think that through, but its all in rotational kinematics.

Talk to me about the SS springs. Are you referring to the straps that prevent the springs from spreading under acceleration? I haven't had the opportunity to experiment with that yet. I did read somewhere that auto cars like to have them completely unstrapped from the axle back, but stick cars do not. Do you have some wisdom for me on that?






I disagree with the masking statement. Your 1st gear will impose the biggest angle change due to axle wrap due to the tall gear. I did have a very slight vibration at around 70 mph +, so that suggests that there was a very small difference in drive angle and pinion angle. The car drives very smooth now even at 80 MPH. Also, I want to point out that with such an aggressive clutch, you cannot have differentiating velocities between the tail shaft and the rear end. Differentiating velocities is a result of not having equal and opposite angles between the clutch and the driveline. This will cause the clutch to have a "skipping" affect during acceleration which is the actual definition of "jerk". This was causing the clutch to grab and let go cyclically (Shudder). That explains the entire problem. With that said, though going with less pressure plate pressure and a non-puck type ceramic clutch would have definitely gotten rid of the shuddering, it would not have fixed the fact that you still have differentiating velocities due to bad drive angle. In the end, that still would have resulted in wearing out the clutch faster. Its all dynamics. I hope this helps explain some of the situation. There are quite a few people who have had this exact same problem and was never able to fix it without swapping to a stock style clutch. If your drive angles are perfect, a puck style ceramic disc is very doable and will take much more abuse.






This is why I do business with folks that care about their customers and their reputation. You show me someone who doesn't trust Dan and I will show you someone I wouldn't pee on if they were on fire. Thanks for all the help brother.

The short straps that wrap the leaves together. Removing them from the rear segments allows more lift on acceleration.....in other words it makes the tires plant harded. I cannot remember if it's referred to in the MP suspension book or not......I think it is but I honestly cannot remember. It's a mod that's been done a long long time though and it works. They should be left on the front segments, though, as removing them there would have the opposite effect.
 
No problem! Here is am image of what you want to look for. Bare in mind that the pinion angle needs to be the same as dive line angle UNDER LOAD. So 5-7 degrees lower is what MP Performance books say per RustyRatRod.

View attachment 1715739755

Trust me, it ain't "per me", it's per Larry Shepard and company. ...and I wasn't trying to argue with the clutch theory, certainly that needs to be right......but in my mind, you want the pinion angle RIGHT before you start chasing demons, because if it's not, you'll keep chasin um.
 
I’d like to thank everyone for this thread, I’ve had a similar problem in my 340 dart but never thought to look at the trans joint angle. As one poster stated it should be the same as the pinion joint angle. I’ve been living with it thinking it was the clutch, I’m going to check the trans joint angle now!
Be sure to let us know what you find. Have fixed many "clutch" problems by simply fixing driveline angles. Just because it's all factory parts, ex: motor/trans/rear doesn't mean angles are correct either. Leaf springs sag, perches were welded on incorrectly, etc.
 
Hope to be able to look at it this weekend. I know the pinion is about 5 deg down, will be interesting to see the trans angle.

On my Dart, the factory aluminum bell housing visibly flexed when the clutch pedal was pushed. I’ve been in a couple of other A body manuals that chattered, wonder if that flexing causes chatter. Lakewood scatter shield fixed that, no flex on mine now.
 
Have not had a chance to look yet, it was so long ago.... but I think that’s what I did.
 
Did you make the transmission centerline parallel to the pinion centerline at rest?

No. I had my pinion CL 4 degrees below the engine/transmission centerline at rest. I figured for 4 degrees of axle wrap during acceleration. My issues came from having the engine/trans centerline 0 degrees with the drive shaft. For some reason, my clutch did NOT agree with that. I shimmed the transmission up and all my issues are gone. Once I install the "pretty" shim, I will reset my pinion angle back to the 4 degrees below engine/transmission centerline and readjust my snubber location.
 
Ok guys, life got in the way but I finally looked over the U joint angles. All was well, about 3 deg on each end. Turns out the shudder was a combination of cam overlap, carb settings, and rear gear. Swapped a 3.91 in (3:23 orig) and it was pretty much fixed. Reset the idle screws and now it’s back to like new. Thanks for all the help!
 
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