Classic/Antique Car Repair: Rear end fluid, filler plug, warm climate

Question
I have a 68 mustang.I am changing third member. The one I am putting in dose not have a fill plug.Do I add fluid at axle? Also how much and what weight?

Answer
It has a filler plug.  Ford used two different designs, one has the filler plug through the rear cover, which is easy to see, but maybe you have the other design in which the filler plug is buried in the fins in the front of the cast housing, on the driver's side - but if you look carefully, you will see it.

I can only guess how much it will take, probably a bit over a quart, but whatever it takes, fill it to the bottom of the fill hole.  Use SAE90W oil in winter if you live in a cold climate, or SAE140W year round if you live in a warm climate (above 32 degrees or higher year round).

Dick