Yamaha BIG BEAR 400 Owner's Manual page 110

In addition, the differential gear oil level must be
checked and the oil changed as follows at the in-
tervals specified in the periodic maintenance and
lubrication chart.
To check the differential gear oil level
1. Place the ATV on a level surface.
NOTE:
The differential gear oil level must be checked on
a cold engine.
2. Remove the differential gear oil filler bolt, and
then check the oil level in the differential gear
case.
8
1. Differential gear oil
2. Differential gear oil filler bolt
3. Correct oil level
NOTE:
The oil level should be at the brim of the filler hole.
3. If the oil is below the brim of the filler hole, add
sufficient oil of the recommended type to raise
it to the correct level.
4. Install the oil filler bolt, and then tighten it to the
specified torque.
Tightening torque:
Differential gear oil filler bolt:
23 Nm (2.3 m·kgf, 17 ft·lbf)
8-18