More on vibrations

[XH29N0G]

I am having a problem with driveline vibration starting at ~40-50 mph.  I see a number of threads on this topic, but do not see them sorting out my issues.  I have some questions and am hoping there are those who can offer opinions on what to do.

The vibration starts at 45 mph when I depress the clutch.   Above 55 mph it is there whether the clutch is engaged or disengaged. It is high frequency (like a rumble strip).  It does not matter which gear I am in or what the engine RPM are.  Tires have been balanced after it started.

The vibration started after I had the gears changed from 3.23 to 4.30, but not right when I got the car back from the shop.  The only thing I can think of that could have been done other than chance is that I stomped on the gas shortly before it started. I would not think this would do it, but someone may know better.

The shop I took it to has looked it over, and has not found anything (lost balancing weights, obvious problems with U joints, visible inspection).  They suspect the transmission, but are hesitant to move forward with taking things apart until it can be definitively diagnosed.  I think they are competent, but cautious.  When I look under the car, I notice a little play in the coupling that links the transmission to the driveshaft and I do not know how much play is normal.

For those of you who know.  Do you have recommendations for other tests I can do, or ask to have a shop do?  My guess is I should take the driveshaft to have its balance checked, but I do not know if something in the tailshaft of the transmission might do it instead. 

Thanks,

James

The car is an original base model charger with benchseat, but 383HP and HD suspension and I am starting the process of restoring it and making it the way I want it. 

[Dino]

It's likely the rear end, did you set the bearing preload? 

[XH29N0G]

I did not do the rear end work myself.  The people I went to were heavily recommended and I believe are competent because they do this type of work on a regular basis.  I have taken it back to them and they have not suggested this as an option.  So if it is the rear end, is there a test I can do, or suggest that may point them that way?  Can you give me a primer on what an incorrect setting on the preload would do to cause the vibration?

[Dino]

I did not do the rear end work myself.  The people I went to were heavily recommended and I believe are competent because they do this type of work on a regular basis.  I have taken it back to them and they have not suggested this as an option.  So if it is the rear end, is there a test I can do, or suggest that may point them that way?  Can you give me a primer on what an incorrect setting on the preload would do to cause the vibration?

I'm sure these guys know what they are doing but for all we know they are not mopar guys and are not aware of this (unlikely but hey we need to check all options right?)

They may have but green bearings in the axle which would eliminate the need for setting end play so check with them first to see what bearings you have.

What I would do is put the rear of the car on stands and remove the wheels and drum covers.  You can grab the axle ends and see if there is any play on them.  If not then this may be the problem. 
Go to the passenger side, loosen the 5 nuts & back the adjuster out a few turns (it's the big circular nut with the notches).  Re tighten the nuts & the adjuster will turn inward very easily without loosening the 5 nuts.  Remove virtually all the end play , seat the axle with a hammer & you should just be able to feel a bump.  There's a small clip on one of the nuts that fits into the adjuster notches so make sure it's set so the adjuster can't go anywhere.

When you take a test drive do take your time as it the axle and bearings need to warm up a lot so the metals can expand.  If at that point you don't hear or feel anything you are good to go.

If none of this is the issue then something must be wrong with the ring and pinion, also make sure to check the u-joint and anything else for excessive play.

[Mick70RR]

I chased a vibration problem for a long time and couldn't get to the bottom of it. Some time later I replaced the rear tyres and the vibration was gone. I'd watched the tyre fitter balance the original tyres and all the weights were still on the wheels so I assumed they were ok. I'd get the rear wheels re-balanced before I looked any further.

[XH29N0G]

I had the driveshaft balanced today ($60) - problem solved.