'I'm not sure yet how that second gear fits into this contraption, but that is not your concern. I need you to get out there and find that third gear.
'The third missing gear was placed in a chest hidden in Emyn Hoedh, the old barrows of the Edain in Haudh Lin, north-east of Gondamon. I'm not sure exactly where it is, but it's said to be in the ruins of an ancient crypt.
'Be wary, though! I've heard rumour that barrow-wights roam those lands.'
Bávor is an artificer tasked with repairing the great lock which opens access to the fabled Vault of the Mountain.
Find the missing third gear
The third Bavor has asked you to recover the third missing gear for the Vault of the Mountain. He warned you of rumours regarding the presence of barrow-wights amongst the old mounds.
Bring the third gear to Bavor
Bavor is in Thorin's Hall.
Bavor will be pleased to begin working with the third gear.
The third gear is actually in Emyn Hoedn, just east of Haudh Lin, 17.9S, 94.0W. and is guarded by a few wights. It is the ruins north marked on the map, between Grimwater and Emyn Hoedn flag.
Be sure to get the Old Bones quest from Nithi as it's objective is in the same place