rear end noise

[1970RT]

I posted this on moparts looking for some advice and thought I'd post it here too.

I'm looking for some educated guesses as to what is causing the noise in my 8 3/4.  It's a 70 charger with 3.23 sure grip.  The sure grip seems to work good, no noise going around corners and it is putting power to both tires.  There is a slight noise at all speeds but at about 35 - 40 it is more of a whine.  The whine is most noticeable floating power.  I can change the pitch by just slightly accelerating or decelerating when floating power.  My first thought was that the pinion nut had either loosened or at least that the crush collar had lost enough tension that it allowed the pinion to move back and forth.  The only other gear noise I have ever had was a old Chevy 10 bolt that made noise under deceleration.  Tuned out the pinion nut was practically falling off.  I put lock tite on it and snuged it back up and the noise went away and it was fine as long as I owned it.  I took the third member out last night and checked the pinion preload with an inch pound torque wrench and it was about 15 inlb as close as I could measure it, definitely not loose.  The gear teeth didn't look bad to me (not that I know anything about gears).  The car makes a little more of a clunk going into reverse than I would expect so my next thought was backlash.  I checked the backlash and it was on the high end of the spec.  I adjusted it one notch less backlash on each side and it then tested on the low side of the spec.  When I put it back together I checked the axle bearings and they seemed good (original tapered style)  I shot some more grease into them and set the axle endplay.  Took it for a drive this morning and its the same, no better no worse.  I have no clue what to look for now.  About the only thing I can think of is to buy a cheap open gear 2.76 8 3/4 just to try it and see if it's any different so at least then I know its the third member.

Anybody have an suggestions?

Anybody close to Duluth MN have a 2.76 8 3/4 that good that they will sell for a reasonable price?

[aifilaw]

check your pinion angle on both ends of the drive shaft to be sure, although that will cause more vibration than whine in most cases.
Aside from that you've checked everything I can think of as well... maybe someone else will chime in.

[firefighter3931]

Usually a whine from the 3rd member indicates the backlash is incorrectly set. How does the wear pattern look on the ring gear/pinion. Was there any free play in the rear yoke after you reassembled it ?


Ron