I am actually wondering why the car should have a front differential at all. While driving on road, you mostly won't need 4WD so front weels will spin freely- the front diff will not be in function. While off road and using 4WD, you will want to lock the front (and rear) differential for best traction. So after all, why do we have the front differential? If I can not find a good reason, I will end up in locking it permanently by welding it together. I am curious for your ideas?