I just changed my rear differential for the first time a few weeks ago, and the oil that I took out was Black or a real dark gray. .. I figured it was just because it had been 17 k mileage, but then I just changed it again last nite (to get the rest of the black crap out) and it was the same black color again ....Is this normal ?

 

Diff fluid should be changed on this car annually or about every 10K miles. Anytime the fluid gets that cruddy, it will not completely drain out, especially if you do it when the diff is cold. Therefore, if you change it again right away, the rest of the remaining crud will get flushed out. You should NOT worry about what it looks like. Diff fluid is notorious for looking like mud. This doesn't mean that the fluid has stopped working.
Now that you've done it twice within such a short period of time, do it on at the interval I mentioned and you'll be fine.

Oops, edited to read: should NOT worry (above)

 

THANKS A MILLION VIPER

 

Mine was black at 4k.

After the initial change, it comes out rather clean at 10-13k intervals.

 

For your interest:

Here is Redline diff fluid. Left was in the diff for about 2500 miles, right is new.


Here is Mobil 1. Left was in the diff for maybe 2500 miles, right is new.


Here is OEM fluid ('04) with about 2000 miles on it on the right, new Mobil 1 on left:


I would consider most of these "old" fluids as "clean", so this is a relative term.

 

Very small change in color for the Red Line stuff, huh!!

 

beautiful glasses i must say

 

very detailed viper

has anyone tried motul differential oil?

 

It was only in there for a very short time. As it turned out, even after such a short period of time, the Redline Shockproof came back with an oil analysis that indicated that it has reached the end of its protective lifespan. It is not a good product for street use.

I should revise those mileage figures now that I've found the thread where I conducted the experiment. It was 2500 mile interval for both the Mobil 1 and the Redline.
Here is that thread:
https://www.s2ki.com/forums/index.php?showtopic=141409

(I'll go back and edit the figures in this thread.)

 

Why, thank you!
(They are about 30 years old and I got a big whack of them for free when I bought Shell gas. So they aren't what you would call "high class". )