I replaced the 7-1/4" rear-end in my 65 Barracuda with a 7-1/4 from a 74 Duster when I upgraded to slider disc brakes. My guess is that the oil has never been changed in the new axle so I thought I would drain the old stuff and fill it with a quart of 75W-90 synthetic GF-5. Rather than sucking it out, I decided to pull the cover to check the condition of the gears.

I didn't see any unusual wear which was expected since it's quiet. However, I see that there is what looks like brown sludge on the bottom. My plan is to let it drain overnight and then refill it after putting the cover back on.

Should I spray in some solvent while the cover is off to more thoroughly clean the insides?

I would................

I'd use paint thinner and an old tooth brush.

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes