Dilapidated cart's bearing old wheel (6)
I believe the answer is:
castor
'wheel' is the definition.
(castor is a kind of wheel)
'dilapidated cart's bearing old' is the wordplay.
'dilapidated' indicates anagramming the letters.
'bearing' indicates putting letters inside.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'carts' with letters rearranged gives 'castr'.
'castr' enclosing 'o' is 'CASTOR'.
(Other definitions for castor that I've seen before include "Fur of the beaver" , "One star" , "Twin to Pollux" , "Oil beloved by parents of old" , "Powdered sugar" .)