what is most common part in the trans to fail? causing the trans to bind up

Its an auto and im thinking by the way its acting that the pin that the spider gears are on has come loose and will slide out and contacting other components

I was in the area...... I was being very general.....I was more leaning towards ring gear dropped-seen that in older Corollas.......EITHER WAY it ain't a good sound to hear. Good luck.