When we need to change gear oil ?

It depends on the make model and year of the car or truck. Slice the recommended mileage in half if you do any towing or carrying heavy loads.When we need to change gear oil ?
about every 40000 klm particles of metal starts to increase wear of the gears and at lest you can see if the magnet in the drain plug is getting a metal flower building on it if it does you have a bearing going outWhen we need to change gear oil ?
The average car will never need to change gear oil. If however you do a lot of towing, or carry excessive loads, 100,000 miles would be sufficient.
its recomended every 50,000 miles to keep it in good shape. if you do heavy pulling probably every 25,000 miles.