third gear noise

[mfp-66]

coming home from work today when i selected third there was a noise and vibration coming from engine/box that felt like the big ends had gone. when i went to any other gear it was quiet as normal.
any one had this problem and know what is causing it? expensive?
dangerous to use?

1980 z1000

[zed1015]

Weak spot is usually second gear but then only after lots of abuse and/or big power increases. Could be bent selector fork (usually caused by a high speed missgear) or teeth shedding to name the obvious. For the least amount of disruption you can take off the sump to inspect the cluster from underneath for any obvious signs of wear / damage and metal particles. Could also be worn dogs, selector drum or mechanism damage etc or something very simple like the selector mechanism working loose or a circlip on a gear shaft coming adrift allowing one of the gears to come into contact with something it shouldn't.

[mfp-66]

found the problem the 3rd gear had a tooth missing and a few chipped. see wanted ads. loks like the cam guide had broke off and dropped into the gearbox doing damage to the gear