The rear axle of my son's car disconnected from the wheel and is now dragging on the ground. This also caused him to wreck into the curb and do damage to the front tire.
There are several components to the rear axle assembly on your vehicle. The GS300 has a drive shaft, a CV axle, and a rear hub bearing assembly. I am guessing your issue is either with the CV axle or the hub bearing assembly. The CV axle is what drives the rear wheel. It comes from the differential, through the hub bearing and is secured with a large nut. It is possible for the CV axle to break but this is not common. Usually if it does break the vehicle just wont drive anymore. If your tire came off, the hub bearing assembly is more likely to be the cause. This is what the wheel and tire are actually bolted to. If the bearing assembly breaks it is possible to lose the wheel and possibly control of the vehicle.
Having a mechanic actually look at your vehicle would be advisable. Since there was a loss of control and damage to the front as well, there could be other secondary damage that would need to be repaired for example brake lines torn, bent brake heat shields and suspension components. A mechanic will be able to determine the extent of damage and what components will need to be replaced.
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