How do I know if I need a repair or the whole spindle replaced?
While we can weld up and machine down a bearing or seal surface to its original diameter, your spindle may not be in good enough shape to do so.
A spindle that has only a slightly galled surface can be fixed. Generally the bearing can be pulled off the spindle. There may be metal transfer from the bearing to the spindle. The other reason for spindle wear is from high mileage. The bearing wears on the bottom of the spindle and causes a groove where the metal has worn away. We can also fix damaged threads. In the event the end of the spindle threads are damaged from abuse or the axleshaft breaks and oblongs the end of the spindle. As long as the spindle end is not split or metal is missing, the end can be welded up, machined down, and rethreaded.
A spindle that has had excessive heat from a burned bearing will be damaged to the point that it needs replacing. Sometimes the bearing is stuck on the spindle and cannot be taken off. Other times the spindle is obviously damaged due the bearing burning up and hub falling on the axleshaft which rides on the spindle. This causes the end to wear thin and split beyond repair. Worst case is the hub and wheels leave the vehicle and the spindle hits the ground causing it to bend. In these cases the whole spindle needs to be replaced.
If you have more than 1 damaged surface, it means the spindle took some abuse and it would be better to replace the spindle.