Fury as bonnet falls off old car (5)
I believe the answer is:
anger
'fury' is the definition.
(fury is intense anger)
'bonnet falls off old car' is the wordplay.
'bonnet falls off' means to remove the first letter (in a down clue, bonnet could mean the top letter).
'old car' becomes 'banger' (slang for an old, dilapidated vehicle).
'banger' with its first letter removed is 'ANGER'.
'as' is the link.
(Other definitions for anger that I've seen before include "Great annoyance" , "blaze of this?" , "Wrath, fury" , "Emotion" , "Spleen" .)