How do you know when to change your rotor?

If you feel pulsating, shudder, or vibrating, when you come to a stop, your rotors are warped. Remove the rotor and take it to a machine shop and see if it can be turned and resurfaced. Usually this can be done one time unless the rotor is badly damaged. The machine shop will determine if it can be resurfaced. If not, you will need to purchase a new rotor. Make sure to replace the brake pads even if they look good when replacing or resurfacing the rotor.