Vibration... after getting rear diff rebuilt...

[UH60L]

So, the good news was, after 6 years, I got the rear diff rebuilt and my car back on the road.  The bad news is that after waiting approximately 700 miles, I took it onto the freeway and at 65 mph I had a vibration sound/feeling that was like a constant waahh-unnn-waahh-unnn-wahh-unnn until I slowed down.

Then over a few weeks and driving it here and there and to a couple cruise-ins and car shows, it now does it at 55 mph and sometimes feels worse when I initially let off the gas.

I called Six States, who rebuilt it, and they said it sounded like a driveshaft vibration, suggested bringing in the driveshaft so they could check it.  The driveshaft, which they built for my car many years ago, has only had between 2000 and 3000 miles put on it due to the car sitting so long.  Dropped it off on Tuesday and they just called and said it's straight as an arrow, nothing wrong with it.

So, any thoughts on if it's the rear end or something else and what else might it be?  I know I have read about harmonic balancers coming apart and getting out of balance.  I do sometimes have a squeak/squeal when I start the engine. (never happens when running or driving, only sometimes when it starts...)

My car is a '69 Charger (R/T Clone, originally 318) 440, 727B, manual brakes(front disc converted, rear drum) manual steering, 8 3/4 rear end was the original 2.76, but after the rebuild it's a 3.23 (no posi)

[will]

How old are the tires? There's a thread on moparts about this .

[UH60L]

How old are the tires? There's a thread on moparts about this .

Well... they don't have that many miles, but actual age, they are at least 6 years old, maybe a little older.  Can't remember if I put them on with the new wheels in 2017 or 2016...

Also, there is some wear on the inside edge of the ones that are now on the back. (front end bushings were all shot...)

Maybe they just need rebalancing?...  I definitely can't afford new tires right now...

[Gold Rush]

I don't know if balancing will cure your vibration but if you do go that route, find a shop that does Road Force Balancing. Had a vibration issues several years ago that was cured using that process when typical spin balance did not.

[UH60L]

I put the driveshaft back on and took it to have the wheels and tires balanced.  They said both fronts were an ounce out, so they fixed them, but they said due to the amount of wear on the inside of the backs (previously on the front) they couldn't balance them.

I went and drove the car and it's a little better, nothing at or below 55 mph.  But between 57 and 70-ish it's just as bad or worse, and it tends to get louder/shakier (I can feel it in the driver's seat) when I let off the gas pedal.  It's a constant vibration when I let off the gas, then it settles back to a waahh-unnn-waahh-unnn-wahh-unnn. (almost feels like a sine wave, increas/decrease over and over)

I don't know if all of what it has could be the back tires.  To me it feels like eaither the rear end or something else in the drivetrain...

[doctor4766]

Can you swap a different set of wheels to test that?

[UH60L]

Can you swap a different set of wheels to test that?

Unfortunately, I only own one set of wheels and tires that fits on my Charger, and my current financial situation is, well, not good.  Can't afford to buy a pair of wheels and tires.  I used to be in a MOPAR car club, but it broke up during covid.  Maybe I'll see if someone from the club could loan me two...  Although I won't rule anything out, to me it really feels more like a drivetrain thing.

I read that the pinion angle can cause vibrations.  I did....just before getting the car back on the road...replace the leaf springs.  The set I installed add extra leafs to the right side to counter torque.  Could that have messed up my pinion angle?

[b5blue]

No choice but to swap front to back to see if issue moves. A messed up front end can really hammer tires.   

[Kern Dog]

How old are the tires? There's a thread on moparts about this .

Moparts??