just finished installing riddler D44 front and rear diff covers a few days ago.
used the ziptie method.

these are the amount I've used (Royal Purple 75W-90)
Front: 1.70 - 1.75 quarts
Rear: about 2.80 quarts

so far with those amounts in the diffs, after long highway driving and moderate offroad driving, no diff fluid puking out and running very smooth.

just thought i'd throw this out there as when i was trying to install mine i looked around and couldn't find a definitive measurement for filling up riddler's front and rear diff covers.

hope this helps

edit:
just found another post verifying the front fill amount

 

But, why would the Jeep engineers have specified the capacity for an after-market cover with a larger volume? Or are you saying that the Riddlers are not a larger volume cover? That's why I thought we used the zip-tie method--it ignores the volume and just measures the fill level, which is what is critical. It would seem that Gump's figures are useful for those filling D44s plus Riddlers, but not other brands of covers. Yes, no?

 

Thanks for the input.

I thought about using OEM specs at first, but riddler has a much different shape. as a quick test before the covers were installed, i filled up the OEM cover and the new riddler diff covers with water, and the riddlers held quite a bit more than stock covers in terms of volume. the top half of the two covers are similar but the bottom half of the OEM cover is concaved inwards.

there has been discussions on this on other threads about using different amts for aftermarket covers.

just found this

 

The key is to just be under the centerline of the axle if you can do that and still add a little bit of fluid then it will work great

David

 

I have these. I used a coat hanger, bent it 90 degrees, stuck it in the old cover and made a mark on it. Then I used it as a dipstick for the Riddlers. Works great. If you use this method, make sure you make 2 marks cause the hole in the rear cover is higher up than the front on the stock covers.

 

I don't have Riddlers but when I installed my SOLIDS (Similar shape and volume, fill hole is also higher) I just added another 50-75ml. I accidentally added 2.5 quarts to the front diff instead of 2.375 and I got a little spewage from the breather tube. Drained out ~1/10 of a quart and no problems since.

I would say there's a threshold of about +~.15 quarts max with a new diff cover because of the added volume, anymore than that and It will start to spew.

The main purpose of the groove on the inner side of the diff cover is to dissipate heat away from the gears, not add volume.