Changes of gear depend on them (7,5)
I believe the answer is:
'changes' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.
'gear depend on them' is the wordplay.
I cannot really see how this works, but
'gear' could be 'clothes' (I've seen this in another clue) and 'clothes' is found in the answer.
The remaining letters 'lines' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'of' is the link.
Can you help me to learn more?