Was gloomy about the vehicle (5)
I believe the answer is:
moped
I believe this is a double definition.
'was gloomy' is the first definition.
(I've seen this in another clue)
'the vehicle' is the second definition.
(moped is a kind of vehicle)
'about' is the link.
(Other definitions for moped that I've seen before include "Two-wheeled transport -- was in low spirits" , "means of transport" , "Brooded, hung about" , "Languidly moved" , "Mooned around" .)