2006-2009 Honda TRX680 (TRX 680 FA-FGA) Factory Service Manual, Page 462Get this manual
FRONT DRIVING MECHANISM Remove the oil filler capNORMAL:
Rotate the ring gear several times in both directions of rotationCheck the gear tooth contact pattern through the oil
filler holeThe pattern is indicated by the Prussian Blue applied to the pinionContact is normal if the Prussian Blue is transferred
to the approximate center of each tooth, but slightly
to the heel side and to the flank side
If the patterns are not correct, remove and change
the pinion shim with one of an alternate thickness-
Replace the pinion shim with thicker one if the