1997 Cobra, 60K miles, bone stock. Rear diff is an 8.8, same at GT for
past many, many years.

    I have been noticing quite a bit of noise coming from the rear diff on
the car. At slow speeds (<15mph), the noise is either not there or is
barely noticeable. At higher speeds, it becomes a kinda loud noise,
which is constant in pitch and level a a specific speed. The noise does
not change pitch, level, or go away when I step on the brakes. I do not
have a point of reference for how loud a rear should be in a late model
GT/Cobra, so it might be completely normal.

    I've had rear diff gear sets installed incorrectly in the past which
resulted in 'howl' coming from the rear end. The noise I am hearing is
definitely not the same as the 'howl' I have had in the past, its more
like a dull grinding noise. Like something is rubbing, or a bad bearing
(eg: outer axle bearing).

    I took the rear apart today to try and narrow down the problem. With
the rear on jackstands, I spun the rear wheels. It seems like I can hear
something coming from the rear end while I turn by hand. Its not
obvious, and the rear turns smoothly, but does require a moderate amount
of effort. Again, I do not have a point of reference for how loud a rear
should be, so it might be completely normal.

    Figuring that there might be something wrong, and feeling motivated
(maybe stupidly), I removed the rear wheels, rear brake calipers, rear
caliper mounts and the rear discs. I then turned the rear axles by hand
and the noise was the same. I then pulled the driveshaft and turned the
axles again and still the same noise. I then pulled the center-section
cover, removed the wrist-pin and c-clips and pulled the axles. Neither
wrist-pin or c-clips show any signs of abnormal wear (grooves, galling,
etc). I then turned the gearset by hand, and while it turns smoothly, it
seems to make a moderate amount of noise while turning.

    So basically I *think* I've eliminated rear brake noise, U-joint and
outer axle bearing as sources of the noise. Now I am down to:

    1) Pinion bearing/race
    2) Carrier bearing(s)

    Can I use a torque wrench to see how much resistance the rear gear set
is providing?

    I'd like to hear some thoughts on this.

    Do 8.8 traction-lok rear make a good deal of noise? I had the rear diff
fluid changed at a 'Mr Lube' about a year ago (similar to Jiffy Lube).
They use a vacuum to suck the old fluid out and then put new fluid in.
Now I know that 8.8 trac-loks need the friction modifier gunk from ford.
I know I asked the guy at the Mr Lube if they were going to put the
friction modifier in with the new fluid, and I am pretty sure he told me
that since they were putting in GL-5* 80-90w I didnt need the friction
modifier.

    TIA for your responses.

    Chris

P.S. I am also posting this in the SVT Tech Stangnet Forum.