Thanks for looking -
I've had Mopars for many years, but differentials and axles are unknown territory for me:
I've got a '65 Satellite with a 742 diff and it's has a mild, off-throttle, whining sound.

1.) Is this sound causing harm? (I think not, cuz I lived with a whiny diff in a /6 Dart for over 200,000 miles).
2.) How is a 742 adjusted for noise like this? .... if that's even the right question to ask?

Background:
The 8-3/4" rear end of this car was ALWAYS noisy. It grumbled and growled for about 5,000 miles, took a wicked sudden turn for the worse in 2017 and it was obviously a bad rear bearing. I had a lengthy painful thread here about this. The short story is the old bearing wouldn't come out. It also showed evidence of having been tried removed before, but a previous owner left it and gooped red silicone in the bearings to seal them or some such nonsense. I broke a bearing puller trying, but couldn't pull the axles out past the stuck bearing race. So I cut through the axle tube, destroying the axle housing, and went searching for new 8-3/4" axle housing.

I kept the 742 diff and the old axles with blue/green paint marks.

I bought a used 8-3/4" axle housing with axles but not the diff from a local Mopar buddy. I refurbished the housing, stuck new OEM cone bearings on the axles, put the 742 pumpkin and inserted the axles easy peasy. The "new" axles have white paint marks.

The growling sound is gone, but a whining sound remains. It happens only off-throttle, sometimes not at all, but usually gently coasting.
(My '67 Satellite has its original 741 rear diff and is 100% quiet in comparison).
The whining is not bad enough to transmit any vibrations into the car.

I thought the "new" axles are matched to the "new" axle housing they came from and fit right in with no adjustment needed.

Thanks,
- Art

It never ceases to amaze me the amount of major work people will do without even looking at the FSM.

Right out of the 65 FSM, adjusting your axle end play, though that's probably not the only issue. Sounds like yout pinion to ring gear pattern is off. That would also b ein the FSM with pictures of what is good and what is not good.

IMHO, once a ring & pinion makes noise and runs for any length of time you're not going to adjust the noise away.

I agree, of course though it most likely isn't hurting anything either.

You may want to check the pinion nut and make sure it is tight with no end play present. If neither of those are at fault

The only way to get rid of it is louder mufflers (LOL), and from you description doubtful anything will get hurt.

The axle end play should always be checked.

Only easy check is the pinion nut to make sure the pinion pre-load did not slack off as mentioned above.

My first question would be "how loud"?
Had an unmolested original '69 RR about 20 years ago that had a little whine to it, at 130,000 miles it had never changed.
Had a molested hot rod Duster with a markedly louder whine from its 489 case at certain speeds and at decel, pulled it and the pinion depth was so far off it had eaten the outer diameter of the ring gear.
I think on that deal the guy just stood back and tossed the pinion in from across the room and called it good..!
I don't think a 742 can change its pinion depth from wear like a 489 can, but I could be wrong.

FWIW I've found lower ratio's sometimes whine a little more than higher ratio's...
I know my 3.91 makes a little more sound than the 3.23 does...
A local guy to me sets up a lot of rears in the area...Street cars...drag cars...whatever...The one thing he doesn't do is guarantee they won't make any noise...
Some rears can be set up perfect and will still whine...

Thanks all,

I'll start by checking the pinion bearing. That's the advice I was looking for - where to start. I've sourced an FSM, and will use it to educate myself, just didn't know where to start troubleshooting this. I'll check the other items you suggest after that. Axle end play was fine after the work last year.

It's an AC car with a 2.76 ratio, open diff. The whine is something I could live with - it's not very intrusive. But you know how once you hear a noise it gets under your skin and if it's a system you don't know much about, you gotta start asking. I drove the '65 all last week, played with the throttle to check it out, but the difference *really* hit me when I switched to the '67 Satellite (741 with 3.23 ratio) - that thing is completely silent, so it got me wondering.

I'll have the '65 back next week. If I find something worth sharing I'll post it here.

Cheers,
- Art

The 742 case has shims for the pinion preload so you can just make sure the pinion is torqued to spec. Like stated above if the noise is not increasing than it is probably not eating itself and you could go crazy attempting to get rid if the noise. Some just make noise.

I did a lot of ring and pinions back in the day for whining. I think Mopar stamped those things out with an axe.

You may want to try some different gear lube. I would suggest something like Redline's ShockProof. It may make a difference and quite things down but whining on the coast side isn't far up the list in terms of importance.
R.

Thanks all - the sound is almost gone - here's an update..

I drove the car home from the storage garage, listening the whole time. The whine came only "off throttle", and a lot of the time just not there at all. The sound wasn't really *that* loud after all.. was I dreaming the time I heard it so loud? ...maybe it's quieter with stiffer cold oil?

The next morning, I jacked the rear up, got the driveshaft off the yoke and checked how much play there was in the pinion bearing, just using my hands to yank on the yoke. There was no sideways play, and just a tiny bit of endplay... 1/16"? I noticed a drop of oil hanging from the bottom of the chunk, although nothing had dripped on the floor. The oil looked like it was probably weeping from the pinion seal. I checked elsewhere on the chunk and decided to check the torque on all the axle housing nuts. Well, I was able to tighten each nut a good full rotation. Even though I don't know the torque spec, I tightened them all as equally as I could. I did check the diff oil level last fall, it was right there near the edge of the filler port.

The whine is now imperceptible at speeds above 35-40.. above that speed the noise of the car itself makes it impossible to hear. I'll keep an eye out for oil drips and the oil level.
So thanks for walking me through this..
- Art