Rear Differential Lube Change

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Ingredients /
tools needed:
– 1.69 Quarts of M1 Synthetic Gear Oil (GM equivalent
12378261) SEA 75W-90 (Z06 3.42’s, other gears may vary slightly)
– 4
oz. of limited slip additive (EQUA TORQUE) or GM part #1052358
– A big
‘ole Hex Key, like 1/4″ I think it was ..
– Some rags and a fluid oil
pump ($5 at pep boys, very useful)
Here they
the car up or drive it on some ramps, so you can get under the rear axles.
Then support it, so it doesn’t kill you (:smash:). Next, find the drain
plug on the bottom of the gear box, which there are two of, so don’t get
confused … one is actually on the side, it’s the FILL Plug !
Safey is first
actually used ramps on the rear, but you get the picture, right

The one from the back, is the FILL (It has a little tag
attached to it) pointing rearward and facing
between the rear swaybar and leaf spring … DO NOT GO TO YOUR
This big thing is your
… so let it all
18.5K miles, this is what the old gear lube looked like
In my case, there were no significant “metal” particles or
anything like that – but some have reported a couple of lose gears and
ball bearings (just kidding) – in their gear box, especially all you 3.73
and 3.90/4.11 racers ! 😆
Now … retighten bottom plug to 26
lbs-ft. & pump in 1.69 (about 1 and 3/4, little less — quarts of the new
stuff – as such, using the
In the process, you will add ANOTHER 4 ouches of limited slip diff
fluid, to top it off until little begins to pour out, or to top of rear
fill plug! Don’t over fill it !
Retighten, this second bolt to 26
lb.ft – and drive normal, NO WOT – until 300 miles have passed. Send me
email, if you got more questions. Total time to do this is approx 30-45
mins, if you’re maticulous. Total cost was $30 vs. $140 @ dealer.

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