Driveline vibration

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SlantedDart

SlantedDart

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Really hoping to get some help here. I’ve had a vibration at 70 that I can’t get rid of. It’s a harmonic growl vibration( whom whom whom). More so on decel but still present while normal cruising at 70. I had a bent wheel that was fixed, still there. I bubble balanced the rears still there, one still takes a lot of weight to get right. Now I’m onto pinion angle. I did notice that one of the thrust washers inside the u joint cup was missing. Drive shaft would move in pinion about .050 north and south. Put that in, still no change.
Engine angle is 1.5 down, drive shaft is 1 down and pinion is 3.5 pointed toward ground with shims that calvert said to put in. No change there. I flipped the shims which actually made it more pissed off just to see (pinion up). The only real change I’ve seen was when I moved the weights around on the wheels the frequency of the hum/ vibration changed.
At 70 I push the clutch in and it’s still there. Definitely in the back of the car.. any suggestions? All these parts are new. Drive shaft, 9” rearend, housing, axles, wheels..
 
Did you have the drive shaft made. I had a Volari years ago we put and 8 3/4 in . Had a drive shaft made and they balanced it. They did it again twice.

I found a old original drive shaft in my pile that fit and the vibration was gone. It ended up being the drive shaft u-joints were not clocked the same front to back. If they are off just a little it will vibrate.

Hold it tight on a solid straight Steel beam on its side. Make the caps equal side to side on the front and the rear should be identical. Not saying this is definitely your problem but Something to check. Its something that many overlook.
 
Oldmanmopar said:
Did you have the drive shaft made. I had a Volari years ago we put and 8 3/4 in . Had a drive shaft made and they balanced it. They did it again twice.

I found a old original drive shaft in my pile that fit and the vibration was gone. It ended up being the drive shaft u-joints were not clocked the same front to back. If they are off just a little it will vibrate.

Hold it tight on a solid straight Steel beam on its side. Make the caps equal side to side on the front and the rear should be identical. Not saying this is definitely your problem but Something to check. Its something that many overlook.
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Yeah custom drive shaft. Every time I’ve brought a drive shaft back to get it checked out “nothings wrong with it”
 
x2 on the driveshaft- out of balance, not true, or yokes not clocked right.
And just to eliminate the wheels/tires, rotate them if possible; or throw on a different set (even if you have to borrow them) and see if the vibration disappears or changes.
 
SlantedDart said:
It’s a harmonic growl vibration( whom whom whom).
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IMHO what you are hearing is a heterodyne.

It's the frequency that two other frequencies create, typically it's a low frequency.

Like if 1 tire is making a 1000 hz sound and the other is making a 1100 hz sound the resulting heterodyne frequency would be 100 hz.

As a test, take one rear tire and move it to the front.

Any change in sound?

Rotate the rear tires side to side (now rotating in the opposite direction)

What brand of tire?

If you look at BFG TA Radials you will notice that the treads are not uniform size and they are in a random size spacing. Like large, small, medium, small, large, small, medium, large etc.

The random size pattern reduces the likely hood of a tone being generated

Like when you are on a highway and it has left to right cuts in the road bed, you here a tone, if they are all equally spaced the time is constant. But if the spacing is specifically spaced it plays a song.

This is real.
 
Just throwing this out there. Check for a bad tire.A slight belt break or one that is going bad.
Had it happen to my Dart. Did balance,driveshaft balance. Even had the tires machined trued.
Finally let the air out of the tires and found the problem.
Professor Fate said:
throw on a different set
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Yep.
 
This has happened with different tires. Unfortunately can’t swap fronts to backs. I have 5/8 stud on back and half inch on front. 15x8 back and 15x5 front. Other indicators is that the pinion on rearend is seeping a little bit. Possibly from vibrations.
 
The slicks and radials made same noise. Common denominator is wheels for that instance. Car is smooth as glass up till 70
 
SlantedDart said:
This has happened with different tires. Unfortunately can’t swap fronts to backs
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Understand, you can swap them side to side which will reverse the direction of rotation and if the tone or speed makes a difference it gives you a direction
 
find someone with a road force balancer that will take the tires out of the diag
can be perfect balance and have a heavy spot on the tire or slight out of round or bent wheel
i think your driveshaft is out of true
 
Think I narrowed it down to my wheels. The wheels were fixed but I guess not. I jacked the car up pulled the wheels off and “drove” it at 70. Very minimal vibration honestly what I felt was re verb of exhaust and probably no load of the backlash in third member. Put tires back on and the vibration was back at the same speed..
 
Not the wheels.. thought I got it figured out. Drilled out my old steel wheels for 5/8 studs, went on the freeway, same vibration at 70. Anybody know something on critical speeds. 5th gear is .68 rear gear is 4:30 and tire size is 26. Am I spinning drive shaft too fast. 3.5 inch steel can’t recall how long..
Also like to note my drive line angles are about the same, within half degree how the old 8-3/4 was and that didn’t vibrate.
 
with it on the jack stands in the back run it in gear ,tape chaulk to a stick and lightly touch the front/back of your drive shaft see if its spinning true
 
nutz said:
with it on the jack stands in the back run it in gear ,tape chaulk to a stick and lightly touch the front/back of your drive shaft see if its spinning true
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I will check. Going to check run out of drive shaft, pinion and axles with dial indicator
 
Also be sure the yoks on the drive shaft are aligned.

My dad had a similar issue in 67 when he bought his Dart, the dealer worked on it for a few months they replaced the ring and pinion, tires, and the drive shaft. In my dad's noted he noted that the dealer said the shaft was not assembled correctly and was slightly out of alignment.
 
Dana67Dart said:
Also be sure the yoks on the drive shaft are aligned.

My dad had a similar issue in 67 when he bought his Dart, the dealer worked on it for a few months they replaced the ring and pinion, tires, and the drive shaft. In my dad's noted he noted that the dealer said the shaft was not assembled correctly and was slightly out of alignment.
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How bad were they off? And did that fix it?
 
Are you removing the bevel that the lug nuts center into when you drill to the 5/8 stud size? That bevel is important. It serves two purposes. First, it acts as a "lock" when the lug nuts tighten against it to keep the nuts from backing off. Secondly, it also helps center the wheel. If you remove all or most of the bevel when you enlarge the stud holes in the wheels, that could be the problem.
 
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Ultimately something fixed it enough that my dad stopped pestering the dealer.



I went back through my dad's noted.

Ultimately the dealer in the first 2 years ....

Replaced the ring and pinion
Replaced one wheel due to run out
Rebuilt the transmission
Replaced the driveshaft

And that was the last entry about the beat / howl at between 50 and 70.

His notes say:

"Test drive with factory man Leon Crady (Dad underlined name) up to Overland Blvd and back beat at 72 - howl at 65 back to Claude's up on rack. Leon looks at drive shaft - says it is twisted counter to normal. Looks to be a manufacturing problem, will replace. Will pull windshield to correct leak"

I don't have any info about how much it was off, there is info online about u joint angle tech and what happens if they are off.

Easy to check, with a long straight edge or maybe a chalk line.

I would suspect they if it was off by a degree or two there would be no noticable effect but 5 or more might.
 
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