I will be adding solid diff covers front and rear to my rubi and according to the write up Heavy Duty Axle Differential Cover Installation Write-Up step 14 the rear takes more oil than the rear. 1.35 quarts front and 2.375 quarts rear. If they're both D44s why does the rear need more oil?

 

Axle tubes are larger on the rear 44, front 44 axle tubes really Dana 30 sized

 

Also in the rear the diff oil lubes the wheel bearings at the outer ends of the tubes. In the front the oil is contained inside the pumpkin by the axle seals. (When the seals aren't leaking, lol)

 

Appreciate the info. So the front has inner seals close to the pumpkin, and the rear only has outer seals? The stock front fill hole does look lower than the rear.

 

A quantity number isn't good enough to get the correct amount of fluid in the diffs, especially with aftermarket covers.

The important thing is to get the fluid level a tad above the bottom of the inside of the axle tubes, front and rear.
Some aftermarket covers have the fill hole a lot higher than the stock covers. So, make a little dip stick out of a bent zip-tie. Use it to make sure the level is as described.