Differential Sight / Fill Plug

[Chevrolet1]

Changed the differential oil today, but am having to use the vent tube to fill it back up (slow proces, even with the vent "T" I made. Sight/fill plug won't break free despite hammer taps & WD-40, but I'm also using a 3/8 drive extension and don't want to push it too hard. Is there a special tool that this this square cavity better?

[txab]

This is why you always break the plug free first, before removing the cover. Use something like PB Blaster or Kroil for frozen nuts/bolts. You can also apply heat in some cases.

 

How are you determining proper fill now?