Ok,
Every year before Woodward, I go under the car from front to rear, grease, oil change,etc.
I checked the level on the differential through the hole in the center section, which is not original to the car, and it was low, which I thought was strange, so I toped it off.
Then I noticed that the fill hole on the center section and the fill hole on the rearend housing are at different levels. The one on the housing is an honest 1 1/2 inches LOWER. I figure, volume wise, about a quart.
So the question is, wich would you use to determine "Full"?

It's to compensate for the roatation of the earth since you're in the northern hemisphere.

Go with the center chunk hole. It's there to keep the pinion bearing oiled... Any lower and maybe a hard launch and drive might thin it up until the momentum equalizes. More is probably better than less in the pumpkin...

Maybe check if either is above the bottom of the bearings.

 Not an expert, and in a pinch, would defer to the guys that answered already. But what makes me wonder is whether either fill is above the level of the wheel bearings? I would guess that you would not want standing fluid in the tubes. Wheel bearings are not sealed, so I would expect if the level is too high there might be some seepage?

Could that be a real issue over long term?

I always use the hole in the center section

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You can't condemn the bad if you don't commend the good

Well, that's better than having a case with no plug and a housing with no plug.......

I have seen fill specs that vary. Some books say 9 pints some say 7 pints.

Many drag racers run the fluid level low. That stuff is sticky enough that it stays in the bearings and as long as the ring gear is slinging it you're good.

There are axle seals at the end of the housing outside of the bearings.

I always use the one on the center section. The one in the housing, if you look in it with a flashlight, seems to just cover the bottom 1/2 inch of the pinion, but what the heck, its where the factory put it.
The one on the center section brings it up to just shy of being level with the axle tubes

That seems logical to me.

I also agree that putting a drain hole at the bottom of the carrier is a good, very good idea... Never could figure out why the factory stopped installing drain plugs.No drain plugs on gas tanks, Automatic transmission pans, rear ends...its like they want you to neglect changing fluids.

Never could figure out why the factory stopped installing drain plugs.No drain plugs on gas tanks, Automatic transmission pans, rear ends...its like they want you to neglect changing fluids.

money

They save $5.00 a Car. One million cars..more money in the Big guy's pocket. American Corporations are run by People whom came up thru Finance....(beancounters) German Corporations are run by men whom came up from Enginering.......You decide! I have a magnetic drain plug in my 9 inch, owner installed.

Glad Steve and Tom gave the right answer. Money talks in the "American" car business. As new car owners kept cars less time the bean counters questioned long term maintenance. Sealed bearings and elimination of zirk fittings and fill plugs saved a lot. Once they figured out how to broach the decks on thin wall engine blocks without crushing them, they had a party.