Video tutorial on how to check a rotor for warpage. Rotor warpage is usually caused by extreme heat from either hard braking, riding the brakes, or having a stuck caliper assembly. Other reasons for warped rotors can be from poor machining when having them resurfaced or from new when a manufacturer has inadequate quality control. Warped rotors will cause a vibrations in the steering and a pulsating pedal when the brakes are applied. This particular vehicle I am working with is a 1998 Ford Ranger equipped with a 2.5L 4 cylinder.
- magnetic base
- wheel wrench
- axle/jack stands
- ratchet and socket set
- dial indicator
Jack your vehicle up safely and remove the wheel. I have removed the brake caliper and pad to remove any drag and also to provided an easier area to setup my instrument. Set the magnetic mount in such a way so the dial indicator is able to ride on the surface of the rotor. In this case I have it mounted to the lower control arm. It is the best practice to mount it directly to the vehicle to reduce the chance of any movement between the vehicle and measuring instrument which allows for maximum accuracy. You can also mount it to the caliper carrier, steering knuckle, strut or any other stationary object that does not move. Mounting it to a floating caliper would be incorrect as there is the chance for moving. Preload the dial indicator to about one hundred thousandths of an inch and ensure the clamps and magnetic mount are security in place. It is important to have the dial indicator riding closer to the outer edge of the rotor as it will show the max runoff. Now rotate the rotor and watch the dial. Max runout will depend on vehicle manufacturers, some vehicles maybe 0.001 or 0.003. Depending on the design of a braking system, some vehicles can be easily affected by the smallest of runout. As an example, I have pulled back the plunger on the dial to falsify a warped rotor.
If your rotor is separate from the hub, then it is also important to do the same procedure to the hub to check for runout. The rotor must be removed and then take a reading from the hub face. It is also important to ensure both the hub mounting surface and the backside of the rotor is clean because this can cause runout as well. Here is a test using a brand new rotor.