Plead to exchange bicycle part (5)
I believe the answer is:
'bicycle part' is the definition.
(I know that pedal is part of bicycle)
'plead to exchange' is the wordplay.
'to exchange' indicates an anagram.
'plead' is an anagram of 'PEDAL'.
(Other definitions for pedal that I've seen before include "cause a revolution in cycling?" , "One of two a cyclist needs" , "Foot-operated lever" , "Lever operated by foot" , "related to feet" .)