Copper breaks into a clapped-out car with precision (8)
I believe the answer is:
accurate
'with precision' is the definition.
(precision is accuracy)
'copper breaks into a clapped-out car' is the wordplay.
'copper' becomes 'cu' (chemical symbol).
'breaks into' means one lot of letters goes inside another.
'clapped-out car' becomes 'crate' (term for an old car).
'a'+'crate'='acrate'
'cu' going inside 'acrate' is 'ACCURATE'.
(Other definitions for accurate that I've seen before include "Factual" , "Care a cut is exact" , "Precise, correct" , "Spot-on" , "telling it like it is" .)