12 bolt rear axle may be going out?

[84Silverado4x4]

I have a 12bolt rear axle in my 84 k10 that was in the truck when I bought it.  I know it has a locker and I was told it has 4:56 gears in it witch appears to be true with the tire per driveshaft revolution ratio.  The truck has a weird noise when I cost in OD with no load on the rear.  If I shift down to drive the noise goes away.  Also I can grab the rear yoke and it will rotate about a quarter turn or maybe a little more with free play.  Any ideas what my be going on in my rear end or is it the type of locker it has?  Other than these issues the rear end is quiet and works fine.

[mcintyrederek]

A quarter turn of free play sounds really excessive.  Take the cover off and drain the oil in a clean pan in case you want to re-use.  Get a new gasket from any auto parts place.  They're under $10.  Examine what's going on in there for yourself.  You won't have much money in it and not a whole lot of time, either.

What kind of trans. are you running with O/D ??  700R4 ??

[84Silverado4x4]

I had it apart a bit ago to fix a leak and didn't see anything that stood out.  Oil was clean and no metal flakes or anything.  I am running a 5.3 vortec out of an 06 pickup with a 4l60e o/d trans.  The noise I have was present with the old drivetrain 350 small block with 700r4.  I also rebuilt the np208 transfer case when I did the engine and trans swap. I never noticed the play in the rear end yoke before and now I'm thinking that must be my noise culprit.  I'm not sure what type of locker is in it but it's quiet and works well!   

[Captkaos]

It is actually moving 1/4 of a turn?

[84Silverado4x4]

Yeah...it has about a quarter turn of play in it.  I'm guessing it's on borrowed time.  I'm baffled it keeps working but I don't even know how it can have this much play in it and work as well as it does.  The only indicator besides the play that something is wrong is the noise it make on coast in O/D.  The minute I manually shift it into 3rd the noise completely goes away.  It works great otherwise and is completely quiet.  I have used some of the new eaton soft lockers that have a worm gear in them and they operate a lot different than a limited slip or Detroit locker and so I thought maybe it was one of these lockers.  I'm now thinking there is an issue and my rear end is coming apart.

[mcintyrederek]

If you just run the transmission in "D" (3rd) do you ever hear a noise?  Seems like if it was a rear end problem, you'd hear a noise in whatever gear you were running.  When a transmission goes into O/D, there is a set of planetary gears that are constantly in motion, unlike when you're running in 3rd or just a normal GM 3 speed transmission, when it's in 3rd, there are no gears rotating, the planetary is locked together and you're running 1:1..  I have heard of O/D gears making a whining noise in 200-4R's and such.. 

But then again, if you're free-spinning 1/4 of a turn, that kind of sums things up.

When you're rotating 1/4 turn of free play, is that turning 1/4 of a turn and the driveshaft is not moving during that 1/4 of a turn, or is the driveshaft moving, and there's 1/4 turn of play in the transmission?

[84Silverado4x4]

The play is all down at the rearend.  I can grab the rear end yoke and give it a 1/4 turn before it will want to turn the wheels in either direction.  I can hear the noise for a split second when I let off the throttle in 3rd but the noise is constant in O/D when coasting until the truck downshift to 3rd.  I had this noise with both the 700r4 transmission and now my 4l60E and the noise is identical.  I always thought it was the trans but now that I have the same exact noise with the trans and I rebuilt the T-case I am thinking it is the rear end and the play in it is pointing me that direction.

[84Silverado4x4]

I now know that the play in my rear end is considered normal.  I have a Yukon grizzly locker and they said the rear yoke could move up to a third of a drive shaft rotation before engaging the locker.  I don't think the noise is coming from my rear end but I still have it.  I know it's not the transmission and I recently had the transfer case rebuilt but the noise does seem centrally located.  It make the noise in overdrive on coast only and either in 2 or 4 wheel drive.

[84Silverado4x4]

Update.  The noise looks to be from improper gear lash in the rear end.  It was pretty far off.  I had a shop set the gears correctly but it doesn't seem like it took care of the noise... Looks like I will need a new gear set to solve the noise problem.

[84Silverado4x4]

Another update!!     So I bought a new motive gear set all new bearings, seal, gaskets, etc. and guess what?!  I still makes the noise!!  The shop is pointing to the yukon grizzly locker in the diff and saying the design with all the free play in it is the culprit.  Anyone else have any ideas about this?  The noise is driving me crazy but I can't afford to keep spending money and chasing my tail!