A buddy of mine has a 94' timberwolf, he changed the front brakes. After he spun both wheels.(forward & reverse). Then he proceeded to go to the back tires to do the brakes there. He tried to spin the wheels, but they wouldn't move. This bike is all time 4wd. Any ideas why he cant get the back wheels to move ,when the front are? He had all 4 wheels off the ground.

 

It might be due to the limited-slip differential?