Coach that's kaput - its back-end's come off (3)
I believe the answer is:
bus
'coach' is the definition.
(synonyms)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for bus that I've seen before include "Use transport" , "Public transport vehicle" , "People carrier" , "Coach" , "Large passenger vehicle - small business!" .)