Location of Drain Plug on Rear End Differential 1972

[Ark Bigfoot]

I have a 1972 Bronco with "posi-traction" rear end. It is making a banging noise about every 5-8 feet around a corner . I disconnected the drive shaft and drove it with the front end and it still made the noise. Eliminating the U Joints. Was told perhaps needs additive added to the differiential oil. Where is the drain plug where I can put this in and your thoughts about the noise.

 

[Rustytruck]

the fill plug is on the side of the cast iron center section there is no drain plug you have to use a small suction hose either down the fill plug or remove the axle vent and go down that hole or pull the axles and then pull the pumpkin to drain which needs resealing back up before adding fluid. none of it is quick or fun.

 

[Ark Bigfoot]

I found the fill hole under mud and filled it up with the posi-traction grease oil and it fixed the issue after driving it back and forth about 100 feet. Took about 20 trips. Works now and is releasing. Thanks