If you suspect that one of your rotors has gone bad, here’s a way to save money: inspect the rotors yourself instead of paying a shop to do it. It’s pretty easy to evaluate the condition of your brake rotors if you have all the right tools and this guide.
Basically, the inspection process involves lifting your truck, removing the wheels, and then thoroughly inspecting each rotor to see if you find any issues.
Lifting Your Truck and Removing the Wheels
For safety, always put your truck or Jeep on jack stands after lifting it.
Once you have the wheel off, you can take a look at the condition of the brake rotor. Here are a few important things you should check:
1. Disc Surface Condition
The condition of the disc surface is the first thing you should check. When you have the wheel off, inspect the front and back of the rotor for:
- Burn spots: This usually means that the rotor should be replaced. If burn spots are minor, they may be turned or sanded off. If they are larger, the composition of the disc in the burn area has hardened. This makes the rotor extremely difficult or impossible to turn.
- Cracks: Minor hairline cracks are normal. If you see any larger cracks, the rotor should be replaced.
- Unusually Deep Grooves: Minor uneven wear is ok. Deep grooves may result in discarding the rotor if they can’t be turned out on a lathe.
It’s normal for rotors to thin out over time due to repeated contact with the brake pads. Rotors that are too thin are dangerous because they’re unable to absorb and dissipate heat effectively. They can also warp and seriously compromise your truck’s braking performance. If a rotor wears too thin, it must be discarded as soon as possible. Here are a couple of things you can do to determine whether your rotor has become too thin:
Look for the rotor minimum thickness, which is a good number to use to determine if the rotor is still safe to use. It should be stamped on the edge or hub of the rotor. Next, use a micrometer to find out how thick it the rotor is. If it is below minimum thickness, the rotor must be discarded for safety. Rotors that are too thin can cause a couple of problems:
- As they have less metal, worn rotors cannot absorb and then shed as much heat as rotors within spec. The excess heat gets transferred to the pads and caliper, and leads to brake fade.
- The caliper piston can extend too far. This can lead to damaged seals and leakage. In the worst case, the piston can pop out.
Also look for uneven wear of the rotor plates. If one plate is thinner than the other, that indicates the caliper is not moving freely. It should be repaired or replaced.
Disc Thickness Variation
If the rotor is still thick enough, it’s time to see if the disc thickness is uniform. The disc thickness variation (DTV) can be measured with a micrometer. Find the thickest and thinnest parts of the rotor, measure each area, and then calculate the difference between both areas. The DTV should be no more than 0.001 inch. DTV of more than 0.001 inch can usually be corrected by turning the rotor on a lathe. If you don’t turn the rotor, you will most likely feel the DTV in the steering wheel.
Sometimes braking vibrations are caused by a rotor with excessive runout. Rotors are supposed to rotate on a perfectly flat plane. If this isn’t happening, the variation from perfectly flat rotation is called runout. Runout can be caused by the disc or the hub.
Disc runout can be measured with a dial gauge. If there is any runout, it means that the surface of the brake is not spinning on a perfectly flat plane. Ideally, the runout should be less than 0.002 inch (or 0.05mm). More runout than this will be felt in the brake pedal or steering wheel.
Automakers commonly recommend replacing the rotor if the runout is more than 0.004″. Disc runout should always be measured with lug nuts tightened to the correct torque spec.
Disc runout can be caused by:
- Overtightened or unevenly tightened lug nuts
- Rust between the hub and rotor
- Rotors that have been turned to beneath minimum thickness
Disc runout can also be caused by underlying hub runout. If you find disc runout, you should also check the hub for runout.
A brand new hub and bearing assembly should have runout of less than .000″. Some automakers spec a max runout of 0.0015″. (It’s still a good idea to check a service manual to see the max runout spec for your truck.)
Any runout at the hub is magnified by the rotor due to the rotor’s larger diameter. So it is critical that the hub runout is within spec.
Hub runout has a few potential causes:
- Worn bearings
- Mis-assembled hub and bearing assembly
- Collision damage
- Rust on the wheel mounting surface of the hub
Tip: Use a wire brush to remove surface rust before checking the runout on a used hub.
Got any questions about inspecting your brake rotors? Please contact us!