Is it absolutely necessary to change the larger bearing on the differential spool when changing the smaller outer bearings?

What is the downside to only changing the smaller ones?

Reason I ask is because I've noticed alot of members here mentioning the differential bearings (smaller ones), but no mention is made about changing the larger one.

Also, since my car had been leaking and leaving little puddles, I found myself topping the tranny oil level off before driving to be on the safe side. Last night when I started my car for the first time in a couple of days I noticed a rather audible clanking sound on start up. I cut the car off and have not cut it on until I could get the bearings fixed. The noise came from the tranny.

Any idea what that could be?

 

You should change all bearings that are bad...inspect them (or have them inspected) and see if they need replacing.

Clunking sound at startup, or when you release the clutch?

 

The clunking sound came upon startup.