2000 Dakota - Odd loud whine from rear end

From: Matt Beazer (teseract@enchantedbookstore.com)
Date: Mon Jan 12 2009 - 19:15:59 EST


A friend of mine has a 2000 Dakota SLT, 4.7L, 4x4, 5 speed manual with
the "handling package", 9.25" rear end with factory limited slip.

For the last year or so, it's been making a loud "whine" from the rear
end that is speed dependant, but not throttle dependent. It starts out
from a stop with a low noise, then peaks at 35mph, quiets down until 45,
gets really loud, and keeps doing this through 75mph. It's like an odd
resonance that can get loud enough to really annoy your ears and make
talking in the cab difficult. We had originally changed the diff fluid
6-8 months prior by using a suction pump in the fill hole, then used Red
Line "Shock proof" gear oil that had the correct rating per the owners
manual, but that seemed pretty thin and looked (and smelled) like yellow
puss. So we dropped the cover completely after the noise started and
cleaned it out and re-filled with Royal Purple gear lube. This quieted
it down by an order of magnitude, but it's getting louder again.

Does anyone have any ideas on what this likely is? Like I said, it's
not throttle dependent - you can put the truck in neutral and coast and
get the same noise. It's just completely speed dependent and
considering the Royal Purple quieted it down, it's definitely coming
from the rear end.

Thanks,

MattB



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