Vehicle backed into unusual kind of engine (8)
I believe the answer is:
traction
'kind of engine' is the definition.
'vehicle backed into unusual' is the wordplay.
'vehicle' becomes 'cart' (cart is a kind of vehicle).
'backed' says the letters should be written backwards.
'unusual' indicates anagramming the letters.
'cart' written backwards gives 'trac'.
'into' is an anagram of 'tion'.
'trac'+'tion'='TRACTION'
(Other definitions for traction that I've seen before include "(In orthopaedics) the pulling on a bone or limb to relieve pressure during healing" , "Pulling power" , "Gripping power to permit movement" , "Continuous pull on limb in medical treatment" , "Action of drawing or pulling something" .)