In vehicle, after argument start to brandish heavy implement (7)
I believe the answer is:
crowbar
'heavy implement' is the definition.
(type of heavy tool)
'in vehicle after argument start to brandish' is the wordplay.
'in' indicates putting letters inside.
'vehicle' becomes 'car' (car is a kind of vehicle).
'after' is a charade indicator (letters next to each other).
'argument' becomes 'row' (to row is to argue).
'start to' indicates taking the first letters.
The first letter of 'brandish' is 'b'.
'row' next to 'b' is 'rowb'.
'car' going around 'rowb' is 'CROWBAR'.
(Other definitions for crowbar that I've seen before include "Levering tool" , "Powerful opener" , "Tool for breaking and entering" , "Purchase may be obtained from this" , "Jemmy" .)