Possible diff/tranny issues - 85 Rx-7

My 1985 IT-A Rx-7 has the 4.77 Limited Slip from the front of a Kia Sportage. Ran the car this weekend and it seems to have started "howling" - sorry I don't have a better way to describe it.

Diff had Mobil1 75-90 LS GL-5 gear oil in it with less than five hours running time. Drained the diff fluid today. It is very dark gray - like way old coffee (with cream). The magnetic drain plug had an aspirin-size amount of goo on it and there seem to be some teeny silvery pieces in suspension. I drained it into an empty clear soda bottle to see what settles out.

Here's another video that may help with diagnosis -
Direct link - "http://www.youtube.com/watch?v=hO2t7Ko5d_I"
[ame]http://www.youtube.com/watch?v=hO2t7Ko5d_I[/ame]

Attentive readers may recall my earlier post with possible rear axle issues. I'm not sure if this is related -
https://improvedtouring.com...ad.php?t=28967

Any ideas? Thank you for the help!

Need to check the bearings in the diff first.

When you put the new gear in did you use the spacer behind the main pinion bearing from the new gear or the diff you put it in? These are factory ground to set the pinion depth in the housing and unless you have the proper factory setup tools it is most likely wrong and only contacting part of the gear face. Did you use gear paste to see the tooth pattern?

Thanks for the help. I've pulled the axle: turning the input or either wheel by hand gives smooth, even motion with no jerks or rough spots (diff fluid drained).
SEckerich - I didn't set up the rear, so no info. It was done at least two seasons ago before I bought it, so it's run for a while.
Joeg- I'm not sure how to do this, but there doesn't seem excessive play.
I'll take it to someone who knows these things.

You would have to look at the bearings (and races) to see if they are burnt, galled, etc.

It's primarly a visual inspection. You can also tell a lot by looking at the condition of the ring and pinion gears.

Once again--visual.

Are you feeling any vibration throught the shifter? Checked the drive shaft for play in the joints? Sure sounds like gear whine in the video. I run 75/90 Mobil 1 and change after every weekend.

Don't recall any shifter vibration.
Dropped the axle assembly off with a local racer friend who knows Rx-7s pretty well and I'll report what he finds.
Thanks again for the help and support.

Tardy update, but some info that might be helpful for others.
Turns out the pinion was trashed. Worn to the point where the pinion gear teeth are sharpened like blades. Very sharp. No apparent damage to the ring gear.
A local guru replaced the R&P, rebuilt the LSD and rear axle setup - including rear wheel bearings and more. Said it was "all messed up" so it's hard to say why this happened. It does not appear to a Mobil1 failure - more likely the R&P was misaligned, although not sure why that happened. At least one rear axle had splines twisted since it was backing out of the axle.
Lemme know if you have questions or wanna see pictures, and thank you for the helpful advice.