Break away from predecessors in retreat (6)
I believe the answer is:
secede
'break away' is the definition.
(I've seen this before)
'predecessors in retreat' is the wordplay.
'in' indicates the answer is hidden within the clue.
'retreat' is a reversal indicator.
'edeces' is hidden within 'predecessors'.
'edeces' reversed gives 'SECEDE'.
'from' is the link.
(Other definitions for secede that I've seen before include "Make a formal withdrawal" , "Withdraw from a body, a nation say" , "Withdraw (politically)" , "leave union" , "Withdraw from, say organisation" .)