Inspecting Brake Wear: Pads, Rotors, Shoes, Drums, and Hardware Condition

Inspection Routine Overview: What You’re Looking For

A good brake inspection is a repeatable routine: you check wear surfaces (pads/shoes and rotors/drums), then the moving/support parts (slides, hardware, adjusters), then the sealing parts (boots, wheel cylinders), then the mounting surfaces (hub face), and finally you document what you found and convert it into a parts-and-labor plan. The goal is to answer decision points like: Is this safe to drive? Can it be reused? Does it need cleaning, lubrication, machining, or replacement?

Quick decision map

• Friction material near minimum, cracked, separating, or contaminated → replace pads/shoes (and usually hardware).
• Rotor/drum below minimum thickness/diameter, cracked, heavily heat-damaged → replace (machining not allowed if it would go under spec).
• Uneven wear inner vs outer → inspect slides/caliper function and hardware; fix root cause or new parts will wear the same way.
• Leaks or torn boots → repair/replace leaking component; don’t “pad slap” over a hydraulic issue.

1) Pad Inspection (Disc Brakes)

Step-by-step routine

1. Compare inner vs outer pad thickness on the same wheel. If you can’t see both clearly, remove the caliper and pads for a proper look.
2. Measure friction material thickness (not including the backing plate). Use a pad gauge or a small ruler; measure at multiple points (top/middle/bottom) because tapered wear is common.
3. Check for uneven contact patterns: look at the pad face. A healthy pad usually shows a fairly uniform “swept” area. Edge-only contact or diagonal wear suggests sticking slides, bent hardware, or rotor runout issues.
4. Inspect for cracks, chunking, or separation between friction material and backing plate. Any separation is an immediate replace decision.
5. Look for glazing (shiny, glass-like surface) and heat spots. Glazing often pairs with noise and reduced bite; it’s a sign to inspect for overheating causes (sticking caliper, riding brakes) and typically replace pads.
6. Check for contamination: grease, brake fluid, gear oil, or coolant on the pad face. Contaminated pads should be replaced; cleaning rarely restores consistent friction.
7. Inspect wear indicators (if present): mechanical squealers should be close to the rotor when pads are low. If one pad’s indicator is contacting early, that’s a clue of uneven wear.

Minimum thickness guidelines (practical)

Always prioritize the vehicle manufacturer specification when available. As a beginner-friendly guideline for passenger vehicles:

• ~3 mm (about 1/8 in): plan replacement soon; performance and heat capacity are reduced.
• ~2 mm or less: replace now (safety risk; likely to reach metal-to-metal quickly).

Decision point: If the inner pad is much thinner than the outer pad (or vice versa), don’t just replace pads—identify why the caliper isn’t applying evenly.

Common wear patterns and what they suggest

2) Rotor Inspection (Disc Rotors)

Step-by-step routine

1. Visual sweep of both rotor faces (outer and inner). The inner face is often worse and is easy to miss without removing the caliper bracket.
2. Check for scoring and grooves. Light, shallow lines are common; deep grooves that catch a fingernail suggest accelerated pad wear and reduced contact area.
3. Feel for a lip at the outer edge. A noticeable ridge indicates wear; it’s not automatically a failure, but it hints the rotor may be near minimum thickness.
4. Look for heat checking (fine surface cracks), blueing (blue/purple discoloration), and hot spots. These indicate overheating; severe heat damage usually means replacement.
5. Inspect rust: surface rust on unused areas is normal; heavy rust in the swept area or rust “jacking” around the hat/vents can cause pulsation and poor pad contact.
6. Check for contamination: oil/grease, anti-seize, or brake fluid on the friction surface. Clean with brake cleaner; if contamination has soaked into pads, replace pads.
7. Measure rotor thickness with a micrometer (preferred) at several points around the rotor and across the face (avoid measuring on the lip). Compare to the rotor’s minimum thickness spec (often stamped on the rotor hat or found in service data).

Thickness measurement: how to do it correctly

• Use a micrometer and measure at least 6 points around the rotor, about 10–15 mm in from the outer edge (not on the ridge).
• Record the lowest reading.
• Decision point: If the lowest reading is at or below minimum spec, the rotor must be replaced. If machining is considered, the finished thickness must remain above minimum spec.

Interpreting common rotor conditions

3) Caliper and Slide Inspection (Boots, Pins, Brackets, Clips)

Step-by-step routine

1. Inspect caliper piston boot: look for tears, missing sections, or wetness behind the boot. A torn boot allows corrosion; wetness suggests a leak.
2. Inspect slide pin boots: they should be intact and seated. Torn boots often lead to seized pins and uneven pad wear.
3. Check slide pin movement: with the caliper off, pins should move smoothly by hand. Any binding, gritty feel, or “stuck” pin is a service/replace decision.
4. Remove pins (if serviceable) and inspect: look for rust pitting, worn plating, or galling. Clean and lubricate with the correct brake lubricant; replace pins that are pitted or swollen with rust.
5. Inspect the caliper bracket: check for heavy corrosion where pads ride. Corrosion can pinch pads and prevent release.
6. Inspect abutment clips/hardware: clips should be flat, not bent, and not deeply rusted. Pads should slide freely in the clips without force.
7. Check pad ears/contact points: shiny rub marks are normal; heavy gouging or rust buildup indicates binding.

Decision points that prevent repeat failures

• Uneven pad wear + stiff pins → fix pins/boots/bracket surfaces before installing new pads.
• Pads tight in bracket (won’t move by hand) → clean bracket lands, replace clips, verify correct pad set.
• Boot torn or fluid present → caliper repair/replacement; don’t ignore, because new pads can overheat quickly.

4) Drum System Inspection (Shoes, Drums, Adjusters, Springs, Wheel Cylinders)

Step-by-step routine

1. Remove the drum and observe before disturbing parts. Take a photo first so spring routing and lever positions are documented.
2. Inspect shoe lining thickness and compare primary vs secondary shoe (they may differ by design). Measure at multiple points.
3. Look for contamination: brake fluid (wet, slick) or axle grease (thick, dark). Contaminated shoes should be replaced; also repair the leak source.
4. Check shoe wear pattern: even arc contact is ideal. Uneven wear can indicate out-of-round drum, sticking wheel cylinder, or hardware issues.
5. Inspect the drum surface: look for scoring, heat spots, cracks, and a ridge at the open edge. Light polishing is normal; deep grooves or cracking is not.
6. Check adjuster function: the star wheel should turn and the threads should not be seized. Verify the adjuster lever moves and engages the star wheel teeth.
7. Inspect springs and hold-down hardware: springs should not be stretched, heavily rusted, or heat-discolored. Weak springs can cause drag and overheating.
8. Inspect backing plate shoe contact pads (where shoes rub): grooves worn into the backing plate can cause sticking. Clean and apply a thin film of appropriate brake lubricant at contact points (not on friction surfaces).
9. Wheel cylinder leak check: pull back the rubber dust boots carefully. Any wetness indicates leakage. Also check for frozen pistons (shoes won’t move freely).

Drum and shoe measurement decision points

• Shoe lining near minimum (use manufacturer spec; common guideline: replace when very thin, around a couple millimeters) → replace shoes and hardware kit.
• Drum inside diameter over maximum (often stamped on drum) → replace drum.
• Deep scoring or heat cracks → replace drum (machining only if allowed and still within max diameter).
• Any wheel cylinder leak → replace/repair cylinder; replace contaminated shoes; clean hardware/backing plate.

5) Wheel Bearing and Hub Face Cleanliness (Rotor Seating)

Why it matters

Even a small amount of rust scale or debris between the rotor hat and the hub face can prevent the rotor from sitting flat. That can create lateral runout, which can lead to pedal pulsation and uneven pad deposits. A clean, flat mounting surface is part of a quality brake job.

Step-by-step checks

1. Inspect the hub face where the rotor contacts: look for rust flakes, heavy corrosion, or stuck-on debris.
2. Clean the hub face using a wire brush, abrasive pad, or hub cleaning tool until it’s smooth and flat.
3. Check the rotor mating surface (inside of rotor hat) for rust bumps and clean as needed.
4. Inspect wheel bearing/hub play (as applicable to the vehicle design): excessive looseness can mimic brake issues and can contribute to rotor runout.
5. Re-seat rotor flush to the hub and ensure it sits fully flat before installing the caliper bracket.

6) Documenting Findings and Converting Them Into Parts and Labor Steps

What to record (photos + notes)

• Vehicle info: year/make/model, mileage, VIN (if used in your workflow), brake option codes if known.
• Pad/shoe measurements: inner and outer pad thickness per wheel; shoe lining thickness.
• Rotor/drum measurements: rotor thickness readings and minimum spec; drum inside diameter and maximum spec.
• Condition photos: close-ups of uneven wear, torn boots, seized pins, rotor heat spots, drum scoring, wheel cylinder wetness, hardware corrosion.
• Root-cause clues: “RF inner pad 2 mm, outer 6 mm; upper slide pin seized; boot torn.”

Turning findings into a parts list

Turning findings into labor steps (example format)

Front axle inspection results: LF pads 4 mm/4 mm, RF pads 2 mm inner / 6 mm outer, RF upper slide pin seized, rotor thickness OK but heat-spotted. Plan: 1) Replace front pads and hardware. 2) Replace both front rotors (heat damage). 3) Service/replace RF slide pin set and boots; clean bracket lands. 4) Clean hub faces both sides; verify rotor seating. 5) Reassemble, torque fasteners, verify free wheel rotation, road test for noise/pull.

Use your documentation to justify each step: measurements support replacement decisions, and photos support root-cause repairs (like seized pins) so the new friction parts don’t fail early.

Continue in our app.

You can listen to the audiobook with the screen off, receive a free certificate for this course, and also have access to 5,000 other free online courses.

Or continue reading below...

Download the app