Vibration at 70 mph and checking diff oil levels

[Chryco Psycho]

Vibration is one thing , whine is another , the whine is improperly set gear mesh

[1970GranCoupeConvert]

I bet your driveline angles are setup wrong or that the driveshaft is out of balance (got dinged or a weight fell off).  Read this post:

http://www.cuda-challenger.com/cc/index.php?topic=95284.0

Regarding tire balancing...whenever you get your tires balanced go t a shop that will do a "Lug Centric Road Force Balance".

Most shops will place the rim in a spinner and use two cones to center the wheel assembly in the center hole.  If you are using steel wheels then possibly the center hole is not the exact center of the punched steel rim.  Centering the wheel assembly on the lugs is the "lug centric" part.

The Road Force part is that they will spin the wheel on a machine that has a roller that rolls along the tire tread and it has a very accurate sensor that will measure if the tire was molded out of round.  It will also measure your rim to ensure that it is both "true" (not bent side to side) and round. 

If your rim is not round and your tire is slightly out of round the two errors can be magnified.  A Road Force machine can take the out of round rim and phase it opposite of the out of round tire and cancel out the two errors for a VERY SMOOTH RIDE.  High speed race cars they even go as far as setting up a lathe and spinning the wheel assembly and cutting off the high spot on the tire so the the wheel assembly is perfectly round (but that is super ridiculous for our applications).

[DocMel]

All are def possible issues.   

But I would check that 40 plus year old drive chain FIRST

Do the easiest, low cost options first that you can do at home.  I went thu it all, balancing tires, DS, u joints, wheel bearings, tourque converter and finally came back to the rear dif.  NOTHING got even a little better on my 71  , until I checked the rear end

-U joints all u joint bolts for stability
-Play in rear end yoke

So whats the latest?  What have you checked since  you posted your problem?

[Aussie Challenger]

  The rear end is the last thing I would suspect, they are known to fail but they do not need servicing, just check oil level at regular intervals. Yours is not a LSD so very little to go wrong, yes while the tail shaft is disconnected check for pinion movement up and down.
  The first thing I would check is the U joints, check for slop, if none, undo at rear end and make sure that they are not seized.
  Also check rear trans mount. Wheel balance can also be a problem but at 70mph an out of balance tire would show up at a much lower speed usually.

[DocMel]

I disagree to a point:  While rear ends do rarely fail, its an item that is almost totally neglected when it comes to maintenance   The oil gets low from leaks, thins out and accumulates moisture:  Now add 40 plus years of that and hard use, things do wear and will wear and come out of spec. Metal to metal contact with a poor maintenance history typically starts with a vibration that is very hard to detect:  It eventually gets worse, but little by little, until the driver goes WTF?  Then one day you romp on it, and the dif could fail.  Again rarely will a dif just fail, but worn parts will keep getting worse

My main issue here is don't go chasing down, like I did, AND REPLACING,  u joints, possible wheel bearings, wheel balancing, DS out of balance until you check the easiest things first

-Like said, check U joints, and take the 10 minutes it takes to see if you have a play in the rear yoke.  No one likes bad news in a rear end, so some will chase issue elsewhere, and never isolate the prob:   I was a classic case.  Im sharing what I shouldve done in the first place:  I checked the u joints, but avoided checking a loose yoke = wear in the dif if its loose

I wasted so much time and money on balancing the wheels, driveshaft, replacing u joints, wheel bearings, and nothing got it better in the least until I removed the DS at the dif, grabbed hold of the rear end yoke, and it wiggled around with so much play that I couldnt beleive it, an it wasnt because the yoke nut was loose either. 

Got the dif rebuilt and no  NO vibrations  (finally)   

So what has been ruled out so far?:  Give us an update

[jordan]

I just did my rear end.  Not because of a vibration, but because it is 42 year old!!  The guy I had rebuild it said it was worn out.  The bearings were junk and it looked like the rear end was filled with mud.  It wasnt mud.  It was clutches, and worn bearings settling in the gear oil!  It wasn't that hard to put it back together either.  Just bolt in stuff and an easy adjustment on the pass side axle.  Go for it.  This was my first time too.