Tractor Differential Lock Mechanism 

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Sorry about the quality of this video. We just saw this demonstration piece of the diff-lock mechanism and thought it was worth taking a quick video on a mobile phone, as it really shows the action of the pedal.
Cut-away of differntial housing, so we can see what happens when the diff-lock pedal is depressed. The two rear axle shafts are locked together with the differential lock coupler.
Downward motion from the pedal is transfered along a shaft and then the shifter fork is moved by the action of a cam. The splined lock coupler then engages the two axle shafts.