Makes known the writer is backing band (7)
I believe the answer is:
'makes known' is the definition.
('impart' can be a synonym of 'make known')
'the writer is backing band' is the wordplay.
'the writer is' becomes 'I'm' ('I am', referring to the person who wrote the clue).
'backing' says the letters should be written backwards.
'band' becomes 'strap' (both can mean a strip of material).
'strap' reversed gives 'parts'.
(Other definitions for imparts that I've seen before include "Gives information about armpits" , "Transmits, knowledge perhaps" , "Passes on knowledge" , "Communicates" , "grants" .)