I know the answer is overhaul but still don't understand how it is reached. Brackendale explained it as relating to car A overtaking car B I still don't get it.
Chambers dictionary defines "overhaul" as to overtake or gain upon (amongst other meanings - examine, repair where necessary). The clue is simply a triple definition of the solution.
Some dictionaries are now showing the meaning as including overtaking:
a : to examine thoroughly b (1) : repair (2) : to renovate, remake, revise, or renew thoroughly
2: to haul or drag over
3: overtake
— over·haul \ˈō-vər-ˌhȯl\ noun