Fix up surplus transport (8)
I believe the answer is:
overhaul
'fix up' is the definition.
(thesaurus)
'surplus transport' is the wordplay.
'surplus' becomes 'over' (I've seen this before).
'transport' becomes 'haul' (hauling is a kind of transporting).
'over'+'haul'='OVERHAUL'
(Other definitions for overhaul that I've seen before include "Pass - examination" , "service" , "'Repair, renovate (8)'" , "Examine and repair (machinery)" , "Inspect and repair" .)