Vibration over 65mph

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matt030305

matt030305

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Hey FABO, I’ve been chasing around this issue on my 71 duster for a little while now. It has a 72 340 and a 727TF. It is a rotating assembly vibration from 65mph and up, the faster I go, the worse it gets. It feels as if it’s under the whole car, can’t really target the noise to the front or back.

So far, I’ve replaced:
- all wheel bearings
- brand new driveshaft made from a reputable drivetrain shop
- engine mounts and tranny mounts
- replaced tail shaft bushing
- wheel alignment
- wheels balanced (clip on weights)
- checked differential fluid levels (I have yet to pull out the differential to inspect it but will be doing it very soon)

Is there anything else that I could have missed? I would appreciate the help! Thank you FABO!
 
If the block states its a 72 340 then it is out of a 73 car. That would probably mean its a cast iron crank. If you don't have the original torque converter in the car or balanced for a cast iron crank you will get a bad vibration.

Many times I have seen this issue because of that problem. Something you may want to check. Look at the Damper and see if it has the words cast crank on it behind the crank pulley. That could be your issue. Just had a 360 car here with the same vibration. Do you feel a vibration at steady higher RPM's in neutral.
 
Oldmanmopar said:
If the block states its a 72 340 then it is out of a 73 car. That would probably mean its a cast iron crank. If you don't have the original torque converter in the car or balanced for a cast iron crank you will get a bad vibration.

Many times I have seen this issue because of that problem. Something you may want to check. Look at the Damper and see if it has the words cast crank on it behind the crank pulley. That could be your issue. Just had a 360 car here with the same vibration. Do you feel a vibration at steady higher RPM's in neutral.
Click to expand...
No vibrations are felt in neutral when maintaining a steady, high rpm. Its speed based from what I gathered.
 
When did it start? What was changed prior? Assuming it does not happen while the car is stationary and when revved in park or neutral. Have you checked the drive line angles?
 
Could the drive shaft be to long when on the ground? Also we had a volari here that had a shop do a drive shaft for a 8 3/4. It ended up being the joints clocked wrong.
 
JoePole1 said:
When did it start? What was changed prior? Assuming it does not happen while the car is stationary and when revved in park or neutral. Have you checked the drive line angles?
Click to expand...
That’s the Only thing left to check now… it’s been happening since I’ve had the car. Will be checking the pinion angle tomorrow and buying shims accordingly.
 
With the car at normal ride height, peak under and see if the drive shaft yoke face is almost jammed against the tail housing. Also, try taking the shaft loose at the rear yoke and clocking it 180*. Have you tried putting the rear axle on stands and bringing the RPMs up to see if it is indeed the rear end, of something in the transmission, of engine.
 
Demonracer said:
Have you tried putting the rear axle on stands and bringing the RPMs up to see if it is indeed the rear end, of something in the transmission, of engine
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That's what I was going to say.



Get the rear on jack stands and put it in drive, then steadily increase the rpm till it shifts the do it more till it goes into 3rd. Then increase till your at 65 mph.

Remember to use the brake till both wheels are at a full stop before you put it in park if it's an automatic.
 
It sounds tire or wheel related. Does it change if rotation of tires? Vibration will remain. But feel and sound difference.

Balancing doesn't pickup higher RPM issues.
 
Demonracer said:
With the car at normal ride height, peak under and see if the drive shaft yoke face is almost jammed against the tail housing. Also, try taking the shaft loose at the rear yoke and clocking it 180*. Have you tried putting the rear axle on stands and bringing the RPMs up to see if it is indeed the rear end, of something in the transmission, of engine.
Click to expand...
I have in the past, but I’ll try the 180 degrees rotation to see if that changes anything.
 
Inspect the engine mounts and transmission mounts very closely. Make sure they are not soft and collapsed.
 
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