No drain plug

Probably same reason they don’t put grease zerks in u joints anymore. Maintenance free.

 

Fluid probably drains thru a differential pattern mount bolt. What are we working on- Diff, Model , photo?

 

Probably located on the center section, rather than the housing. As mentioned above it might be one of the lower bolts.

 

If it's fairly new it could possibly be to force most folk to take it to a dealer to be serviced. The majority of folks dont know how, or simply dont want, to split a diff and get it back together without leaks.

 

The lower bolt when it falls out will drain most of the gear oil out but it will leave a space for dirty lube to sit in the very bottom of it?

 

Built to fail technology. The manufacturers have testing lab for the parts. They have calculated the amount of time parts last and compared it to the bottom line profits on getting more money out of you by either buying a new truck or replacing the part.

It's a business model that runs with the statistical risk of having a recall or a lawsuit vs boosting the corporate profits. They lessen the quality just enough to keep you coming back without getting in trouble

 

It always comes down to money. They save $20 per truck because the machining and plug for each axle is another manufacturing step they can skip.

 

What about the bottom-most bolt holding the carrier into the housing? The bolts either side of it have grade markings cast into the head, that one looks blank. Wonder if that bolt is intended to double as your drain plug?