Brake rotors, or brake discs, are an incredibly important part of your vehicle’s braking system. As your brake pads clamp down on the rotors to slow your vehicle, the friction causes wear and tear over time. To ensure safe driving, it’s vital to know how to inspect brake rotors to determine if they need to be replaced.
Failing to promptly replace severely worn rotors can be very dangerous. As rotors wear thin, they have less mass to absorb and dissipate heat. Excessive heat buildup leads to reduced braking power, longer stopping distances, and more rapid wear on the pads themselves. Letting rotors wear too thin also warps and cracks them more easily.
Follow this easy 7-step visual guide to learn everything you need for inspecting rotors yourself. We’ll teach you to spot all the critical signs of wear and determine if a replacement is necessary. With just a few tools and a bit of know-how, you’ll be checking your brake rotors like a pro!
When to Inspect Rotors
We recommend inspecting your brake rotors at least every 10,000 miles. Double check the rotor thickness if you’ve noticed any symptoms like vibration or squealing brakes. It takes less than 30 minutes to complete the full inspection process.
Pick up these tools beforehand to make the job easier:
- Jack and jack stands
- Wheel chock
- Lug wrench
- Ruler or caliper for measurements
Step 1: Check Rotor Thickness
The minimum thickness specification varies by vehicle make and model. Most rotors should be replaced when worn to 18-22mm thick or less.
- Remove wheel.
- Locate manufacturer’s thickness specification often stamped on rotor edge.
- Use a ruler or caliper to measure rotor thickness in 3 places.
- Compare measurements to specification.
- Repeat on all rotors.
If any measurements are below spec, the rotor is too thin and should be replaced.
Step 2: Inspect Surface Condition
With the wheel removed, check the visible facing surface of the rotor disk for issues:
- Cracks – Small hairline cracks may be safe for street use if rotor is in-spec. Large cracks mean replace immediately.
- Grooves – Deep grooves caused by worn brake pads digging into the rotor. Needs replacement.
- Heat Spots – Bluish discolored spots from uneven pad deposits. Causes vibration. Resurface or replace rotor.
- Edge Lip – Raised worn lip around rotor edge. Rotor is too thin.
- Rust – Surface rust is normal. Deep reddish rust that pits/flakes needs replacement.
If any of those wear patterns are severe, the rotor should be replaced right away.
Step 3: Check Rotor Runout
“Runout” refers to side-to-side wobbling of the rotor when it spins. Excess runout causes brake pedal pulsation and vibration.
- With wheel removed, have someone slowly spin the rotor by hand.
- Hold a dial indicator gauge firmly against the rotor edge, 90 degrees from caliper mount.
- Measure runout distance on dial as rotor spins.
- Repeat test on rotor hub mounting surface.
Runout should not exceed 0.003-0.005 inches (0.07-0.13mm). If runout is excessive, resurface or replace rotor.
Step 4: Look for Oil Contamination
Brake fluid, grease, oil leaks, or sprays can soak into the rotor surface over time. This reduces friction and braking performance.
- Check rotor friction surfaces for oily black deposits.
- Clean small amounts of oil with brake cleaner solvent and considered resurfacing the rotor.
- Heavily oil-soaked rotors should be fully replaced.
Step 5: Listen for Grinding
Have a helper repeatedly press the brake pedal with moderate force while you listen next to the rotor area.
Any grinding noises mean the brake pad material has worn completely through. This allows the pad backing plate to dig and gouge into the rotor surface. Severely scored rotors must be fully replaced.
Step 6: Check Hub and Mounting
The rotor attaches to the wheel hub assembly. Inspect that the mounting area is clean and intact:
- Check for damaged studs.
- Make sure the rotor sits flush against the hub mounting surface.
- Look for any debris, rust, or burrs that prevent proper seating.
Correct any issues prior to installing replacement rotors.
Step 7: Decide if Rotors Need Replacement
Based on the full inspection, determine if replacement is required. The rotor should be replaced if any of the following are true:
- Below minimum thickness specification
- Severe cracking longer than 1 inch
- Deep grooves, pitting, or edge lipping
- Excessive or uneven heat spot discoloration
- Runout exceeds specification
- Contaminated with oil or brake fluid
- Grinding sounds due to pad gouging
Replacing brake rotors in pairs maintains even braking. Include new brake pads to prevent re-wearing old grooves.
And that’s everything you need to know to fully inspect brake rotors! Be sure to use jack stands, wheel chocks, and proper supports whenever going under a raised vehicle. Stay safe out there!
Frequently Asked Questions
How much does it cost to replace brake rotors?
The average total cost for front brake rotor replacement ranges from $300 – $700 including labor at a shop. Rear rotors cost $225 – $550. DIY replacement rotors can be purchased for $50 – $300.
Can I resurface brake rotors instead of replacing them?
Yes, resurfacing by machine shops can add life to solid rotors with some wear left and mild imperfections. However, resurfacing also makes the rotors thinner and may not fix issues like cracks or excessive grooving.
What causes brake rotors to wear unevenly?
The most common causes of uneven rotor wear are improper bedding of new pads, unequal brake hydraulic pressures, seized caliper slides, and worn wheel bearings. Address those underlying issues when replacing rotors.
How often should brake rotors be replaced?
With proper driving habits, quality brake pads, and regular visual inspections, most brake rotors last 3-4 years and 50,000+ miles before needing replacement. Aggressive driving shortens rotor life considerably.