Went fast, but stopped short of the summit (4)
I believe the answer is:
sped
'went fast' is the definition.
(I've seen this before)
'stopped short of the summit' is the wordplay.
'short of' is a deletion indicator.
'the summit' becomes 'top' ('top' can be a synonym of 'summit').
'stopped' with 'top' taken out is 'SPED'.
'but' is the link.
(Other definitions for sped that I've seen before include "Rushed" , "Made haste" , "Moved quickly" , "Dashed" , "Moved fast" .)