Shy when fixing wheel again, you say? (8)
I believe the answer is:
retiring
'shy' is the definition.
(I've seen this in another clue)
'again you say?' is the wordplay.
'again' becomes 're' (prefix meaning 'again').
'you say?' becomes 'tiring' (I can't explain this - if you can you should give a lot more credence to this answer).
're'+'tiring'='RETIRING'
'when fixing wheel' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for retiring that I've seen before include "Shunning contact with others" , "shrinking" , "Leaving work - shy" , "Shy; stopping work" , "stepping back" .)