a new rear end 8 3/4 "rummbling" noise...

[culp71]

71 cuda 340 /727 w 8 3/4 3.23 gears. 480 miles.
last two times I drove it I noticed a new noise, coming from the rear end, its a very faint low tone rumble, only when I turn left, and only when under say 15 mph. it never happens while driving the normal roads  but only when turning around or when turning is a greater angle like when turning into/out of a parking lot/drive way, etc.
I heard it a few time during these drives. sounded like to be coming from rear left. again very dense and faint noise but definitely new. everything was completely rebuilt.
I jacked up the rear end and pulled wheels hoping to find excessive axle play, or something inside the brake drum but everything seems tight, clean, and no indication of anything touching anything, rubbing or grinding. before I put wheels back on I rotated wheels with trans in N, each wheel each direction, also tried to pull in/out and tip.  found that if I rotate the drive side forward direction I was able to get the sound to occur. no other movement on either end did it.

Is its a very faint low end rumble , turning sharply but moving slowly forward and to the left only. it also is not constant.

I checked the yoke and it seemed tight with no side to side play, and no in/out.
it is a 741 case and I remember rebuilding it with the shims and setting back lash, and using marking compound on ring gear to get the proper gear mess.

yesterday I took apart entire front end and put in all new bearings etc. hoping it was a wheel bearing but sound did not change at all.

so my question: what do you think it is?

I am hoping axle bearing, incorrect end play etc.? but have a feeling its ring to pinion issue.....

[1 Wild R/T]

What your describing isn't a ring & pinion... It could be an axle bearing... But it sounds allot more like a S/G unit that needs more additive.... Go to your local Ford store & ask for one of these....  Pour it in then go drive a dozen or so figure eights....

[culp71]

my 8 3/4 is not a sure grip equipped unit.
other thoughts?

[1 Wild R/T]

Ring & Pinion noises aren't effected by corners, they are effected by throttle, often you can float the noise in & out by playing with the throttle.... 

Is this rear end new as in freshly built or new as in new to you?

noises cornering are often in the spider gears but can be in the axle bearings....   But normally an axle bearing noise will be there while driving straight but may be more pronounced while cornering...

If the unit isn't newly assembled I'd pull the pumpkin & have a look at the spiders & cross shaft, they have been known to gall on the cross shaft...

[Chryco Psycho]

Re check you end play first , did you repack the axle brgs with grease ? You should hsve .010 end play across both axles but it is adjusted on the passenger side sp seat both axles using a hammer & se how much end play you have on the passenger side

[culp71]

sounds like I should check the axle end play, I will do that tonight. I will try anything "non-invasive" as I really don't want to have to pull the third member as everything is freshly rebuilt, sealed and painted.

I hope its simply that, but still wondering why it never make a sound until now.

thanks

[Chryco Psycho]

If the brg is running out of position in the cup it can take a few miles to make a noise

[culp71]

so, I removed rear wheels, drums, and axles, it did have about 1/8 inch play in the axle's end play. the bearings are still heavily greased, sound silent, have no wear of any kind and look perfect. when I rotate the axle it doesn't make the noise until I slide it in to engage into the third member. damn. again driver side only in the forward direction only. for the hell of it I re packed bearings, put it all back together set the end play four notches back off from "snug" and test drove. noise is still the exact same no change. damn. I guess the third member will have to come out. no idea what else it could be.

it is what I hear people lovingly refer to as a "1 tire fryer" so do these just make that noise when turning....I noticed that it makes the noise as soon as you can feel the rear of the vehicle body kind of roll slightly, the point where you can feel the body weight and momentum shifts over.

[Chryco Psycho]

Well it was worth checking that first at least

[1 Wild R/T]

Did the axle bearings get replaced?  If not I'd consider doing it... The noise coming at the point of weight transfer sounds like an axle bearing...  The noise when the wheels are removed doesn't....   Noises can be tough, especially through the internet... And my hearing hasn't been upgraded to wifi...

[culp71]

yes, during the complete restoration the entire car, everything was rebuilt including the third member, and axles received all new bearings, etc.
rear end has been silent first 400 miles.
but during the last 40 miles this odd noise has shown up.

so another question if I end up having to pull the third member unit out, and replace/rebuild, its currently a 741, would a 742 or 489 third fit right into current housing? and if I have it, more direct wheel drive power would be nicer...so also I understand the open type carrier, but what is differences with tru-trac ,sure grip, posi, etc. and which would have been on a 71 cuda?

[7212Mopar]

Try this

http://www.mymopar.com/index.php?pid=62

I ordered this one on Sunday. Waiting for it.

http://www.doctordiff.com/8-3-4-489-case-third-member.html

[Chryco Psycho]

Any carrier will fit into the housing , tru trac is my favorite , best design by far , it unlocks with wheel input & locks with power , no clutches to overcome at all just gear pitch

[nsmall]

@7212Mopar Can you share what the shipping bill will be on that purchase? 

[7212Mopar]

UPS ground residential delivery $93.57. It is a big chunk of cast iron and steel.