8 3/4 howling badly.

[challngd73]

sounds loose inside when you have it up in the air..no parts rolling around it seems, but I stepped on the gas and when I backed out of it there was a loud howling noise from the rear end.  Wouldnt make the noise unless I let out of the gas.  As I limped it home, it began making the noise all the time, just worse when i let off the gas.  any idea what this ones gonna cost to repair??

[femtnmax]

If your real lucky, maybe a bad u-joint.  Undo the rear u-joint, and rotate by hand.  Is it dry, or is the joint oily.  Also check the front u-joint.  While you have the drive shaft off rotate the pinon gear, try to shake up and down. 
If your lucky, maybe the pinion gear flange nut has come loose, and just needs retightened.  If your differential is the 489 case it has a crush sleeve (may have a large "9" on the drivers side of the case).  If it is the 742 case it has shims, and may have a large "2" on the case.
For the crush sleeve, we used to change the pinion seal, hold the drive shaft yoke with a large pipe wrench, then tighten the pinion nut to take up all the slack, then a little more...like rotating from 1 oclock to 2 oclock.  Put loctight on the CLEANED pinion and nut threads before tightening.
If its the 742, hold the drive shaft yoke, and tighten with torque wrench to specified torque.
If this does not work, sounds like you have something coming apart.  I would then look for rebuilt differential assy, or find one in the parts yard.  We have lots of them in the parts yard here, so may find one at low cost.
After you remove the old diff, then clean the inside of the axle housing real good, all the way down the two axle tubes to get out any debris.  After you go back together then drive it maybe one hundred miles and change the fluid again.
We need more test data to help isolate the trouble.  I would NOT climb under the car, even on jack stands, and run the engine/drive train, although this could help isolate the problem area.
Hope this is of some help.

[challngd73]

lots of info, thanks for the reply.  I will let you know what I come up with.

[DocMel]

If it is indeed the rear end, its not just a matter of replacing "The Part" that is broke.  Remember, if its your original rear end, its 40 years old.   The rear end is the one thing almost no one goes into for routine, and usually, its only when something breaks.  And when something breaks, it usually means other stuff is, or about to do the same, or at least other parts are just about worn slam out.  Regardless, all the parts are very old, and are getting ready to go south as well.  Bottomline, dont go cheap on the repairs.  That is, if you see just one part that is obv broke, you really need to take the time to change out just about every part that is subject to wear.    You will have to take everything apart to inspect everything anyways.   You dont want to take it apart, just replace the obv broke part, to have to take the rear end apart again when another 40 yr old part goes south

[challngd73]

yeah, it depends on how much it will need.  My father offered up a 3.91 suregrip center section that he took out of his barracuda.  Just dont know if that will be completely unbareable at 65.

[dutch]

this might be helpfull

http://vexer.com/automotive-tools/speed-rpm-calculator         

[challngd73]

very helpful, thanks

[challngd73]

So I have the Challenger up in the air now, and dropped the driveshaft.  My center section is the 741.  I am assuming the pinion nut is what is holding the yolk on?  If so, that nut seems to be tight...That mean something is going on inside then?  Can I safely drive this the 20 miles to my mechanic so he can put in the 742 center section with 3.91 suregrip?