Do i need to pay deflect to kill a gear, using Salvage, that is attached to a unit that has Deflect?

No. Salvage targets the gear, not the unit it's attached to, so the unit's Deflect doesn't apply.

Deflect only triggers when a spell or ability chooses the permanent with Deflect (Rule 809.1.c). An attached gear is a separate game object — targeting it isn't targeting the unit, and the unit's Deflect doesn't extend to its gear (FAQ #734). This holds even though killing the gear will cause it to detach.