re: diff fluid black

["William Mitchell" <mitch48@xxxxxxxxxxxxx>]

Jason asks:
This past weekend I changed the differential fluid for my 94 325i with
Redline 75w90.  It currently has 67k miles and I doubt the fluid has
ever been changed before.  The used fluid that came out of the
differential was jet black and pretty thick and gooey.  Is this
expected or bad?  If it is bad, I'm wondering if there's anything else I
should do besides replace the fluid.  Should I be concerned with gaskets
or filters?  The Redline that went in was a translucent reddish color.

<The color is completely normal for that mileage, and the petro based gear
oil is pretty thick to begin with, and only gets thicker with time.

Since replacing the fluid, I've noticed a couple of things.  First,
there used to be an occasional groaning noise from the rear of the car
when making turns.  This has completely gone away.

<This would be one of the benefits of changing the fluid, and particularly
of using RedLine.

 Second, I believe
the car has much less body roll then previously.  Can fresh differential
fluid have that effect or am I just imagining it?  Body roll was a big
concern for me.  It felt like I was always being pulled out of my seat
whenever making turns.  Now it feels more stable; I don't feel nearly
the same pull out of my seat as before.  Am I going crazy?

<Probably.  Changing gear oil will have NO effect on body lean whatsoever.

One more question, is there a jack point in the middle of the rear of
the car?  I'd like to be able to jack up the entire rear and place the
jackstands on the sides instead of doing one side at a time.

<You can jack using the differential as a jacking point.  I've done it, but
some folks don't recommend it.  I see nothing wrong with this if you support
the car on jack stands and relieve the pressure on the diff.


Bill Mitchell

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