3.09 gear set with 3.23's

[MOPAROFFICIAL]

1st and 2nd gear there is Zero vibration all the way to 6500.

vibration happens in 3rd above say 3600-4000.

3.23 gears 100+ mph. Fixed

if you’ve got a driveshaft you want to send me that doesn’t vibrate I’ll gladly try it.

Tail shaft bushing, have you ever replaced it?
Is there a dent of any kind/size on the driveline?

The drums, have they weights or balance marks on them?

Is the vibration centralized to the firewall trans tunnel and do you feel the steering wheel vibrate when it occurs?

Is it in the rear of the car and does it pulsate?

 

[skep419]

Tail shaft bushing, have you ever replaced it?
Is there a dent of any kind/size on the driveline?

The drums, have they weights or balance marks on them?

Is the vibration centralized to the firewall trans tunnel and do you feel the steering wheel vibrate when it occurs?

Is it in the rear of the car and does it pulsate?

I’ve replaced the tail shaft bushing, trans mount.

swapped in a 904 (bought specific b&m plate)

ran a 4 speed for awhile

different driveshafts on all of the above.

pulsating vibration from rear/seat
Changes with deceleration.

I believe it did it without axles/drums but it’s been awhile.

 

[AJ/FormS]

If it changes with the throttle,or power application; it may have something to do with the pinion angle or the springs.
What I did on one job, was install an adjustable snubber and jacked it high enough to force the pinion into a more or less a fixed angle, then road tested it. On that job it turned out to be a bad right-side spring. A new pair with new bushings cured it. Sometimes I get lucky.
On another job, I ran the combo into the vibration zone, and noted the rpm and engine vacuum. Then checked the timing. Then changed the timing a bunch and retested. That cured it. So I figured the engine was vibrating and sending it thru the clutch all the way to the back and into the springs. But it was not perceptible in neutral. So I figured the engine had to be under power. I'm drawing a blank on what it took to cure that one, but it most definitely was in the engine tune.
The Mopar unibodies have a natural resonating frequency at about 50/60 hertz in the A's. With the right gearing and speed the tires can excite this frequency, and send a somewhat annoying whoo-whoo-whoo thru the car.. Mine, with 3.55s, starts at about 50mph peaks at 55 and is gone before 60; So I can't drive 55, lol. I found mine by blasting up to 70, putting the trans in neutral, and shutting off the engine; then coasting down thru the vibration zone, and Hyup, there it was. This vibration varies only a little with gear, tire, or power changes.

 

[MOPAROFFICIAL]

Only common denominators are the car and the engine.

Vibration is or has to be isolated to a specific rpm range if it does it on a lift, no road contact.
That would mean its the motor or bad drivetrain angle perhaps. After diff trans drivelines , rear diffs, tires, wheels, balancers n flex plates... somethings really far off in the motor and resonating into the trans... or the trans builder is making the same mistake over n over...or the entire engine and trans is offset and there is a slight kink at the tail shaft u joint.

Check if the car has been hit in the front and the k member and trans are not inline with the tailshaft/ diff yolk. You can have all the pinion angle adjustments you want..up n down.. but if its at an opposing side to side angle at one end... wahala.