Hallo Together
I may be a little bit stupid, but i don't find the Filler Plug on the differential of my 1973 Olds Delta 88 Royal Convertible. After replacing the Axle-Bearings i hav to fill Oil in the Differential, but ....

 

It will be on the side of the case above the pinion. It will have a square hole (3/8" I believe). It could be stuck so be prepared for that.

 

Thank you! I found it on the right side of the differential, but your are right: is very hard to open, is not until now. I press with my small hydraulic-Jack to the ratchet wrench, but nothing happens ...
(i'm in my garage at home without carlifter)

... never give up: with a little bit of oil and some 'lovely' blows from a hammer the screw is now open!

 

Yeah, those filler plugs can be a real pain to remove. When you do succeed in removing the plug you can apply a compound that will resist the plugs natural tendancy to wield it self to the diff. There are several brands, i use permatex anti seize, on any fastner thats exposed to heat or corrosion. It makes removal a lot easier.
Good luck, 64 olds charlie