Brake shoes take the brunt of the work in a drum brake system. Every stop creates heat, friction, and stress that slowly wear down both the shoe’s lining and its metal frame. Most of that wear happens gradually — but if it isn’t caught during inspections or maintenance, it can lead to reduced braking performance, uneven wear, or violations during roadside checks.
Brake shoe damage isn’t always obvious at a glance, but it tends to show up through specific wear patterns, surface changes, or hardware issues once the wheel end is opened for service. Knowing what those signs mean helps maintenance teams make smarter calls about when shoes should be replaced — and avoid surprises when it’s time for inspection.
Core Damage: Structural Failures in the Shoe Body
Core damage refers to problems within the brake shoe’s steel frame — the part that supports the friction lining and transfers braking force to the drum. These structural issues are usually only visible during inspection, but they’re among the most serious signs a shoe has reached the end of its service life. Even if the lining still looks usable, a weakened or corroded core can’t distribute pressure evenly across the drum, leading to vibration, uneven wear, or reduced braking performance.
Elongated Anchor Pin Holes
Anchor pin holes can wear out over time from repeated braking pressure and movement at the ends of the shoe. When the holes become oval-shaped instead of round, the shoe no longer fits tightly on its anchor point. That extra play changes how the shoe contacts the drum, which can cause uneven wear or slower brake response. Once that wear starts, the shoe body is no longer serviceable — replacing just the linings won’t correct it.
What to look for:
- Oval or worn anchor pin holes.
- Noticeable movement or looseness when moving the shoe by hand.
- Uneven wear or drag marks on the drum near the anchor end.
Broken Welds or Bent Webs
The web is the rib support that connects the shoe’s outer edge to the table — the flat section that holds the lining. If the shoe has been overheated or over-adjusted, that web can bend or crack at its welds during heavy braking. A bent web prevents the shoe from applying even pressure, which can lead to vibration or reduced braking power. It’s a structural failure, and it means the shoe is flexing every time the brakes apply. A shoe in that condition should be replaced immediately.
What to look for:
- Cracked or separated welds at the junction of the web and table.
- Visible bends or twists along the web plate.
- Uneven contact marks on the drum surface.
Rust and Corrosion on the Shoe Table
The shoe table — the flat surface under the lining — can corrode when moisture or road salt gets between the lining and the steel. As rust builds, it expands and pushes the lining outward, a condition known as rust jacking. This can lift or crack the friction material and eventually cause it to separate from the shoe. Once corrosion starts, the shoe needs replacement, and plated or e-coated cores should be considered for longer-term protection.
What to look for:
- Flaking rust or corrosion under or around the lining.
- Lining edges that appear lifted or separated from the shoe.
- Discoloration or cracking caused by corrosion buildup.
Flattened Rollers and Hardware Damage
Rollers transfer motion from the S-cam to the brake shoes, and they need to roll smoothly for proper operation. When they become flattened, pitted, or seized, the shoe can drag against the drum or fail to release completely. This creates extra heat and shortens lining life. When you’re replacing shoes, it’s good practice to inspect or replace the rollers, return springs, and bushings too. Otherwise, the new shoes may start wearing unevenly right away.
What to look for:
- Flat spots or grooves on the rollers.
- Sticking or slow shoe return after brake release.
- Excessive heat discoloration or drag marks near the cam end.
Lining Issues: Damage and Wear on the Friction Surface
Brake linings are designed to wear gradually with normal use, but once that wear goes beyond limits or shows certain defects, it becomes a compliance issue. During inspections, linings are one of the first components checked for out-of-service conditions under FMCSA §393.47 and CVSA brake criteria. Linings that are cracked, oil-soaked, loose, or worn below the minimum thickness can all result in violations or failed inspections. Catching those signs early helps maintenance teams schedule replacements before they become roadside problems.
Worn or Thin Brake Shoe Linings
Per federal regulations, brake shoe linings must maintain a minimum thickness of ¼ inch (6.4 mm) on non-steer axles and between ¹⁄₁₆ and ⅛ inch (1.6–3.2 mm) on steer axles, depending on the lining style. Once they wear near those limits, braking performance begins to drop and the vehicle risks an out-of-service violation during inspection.
Visible rivet heads or wear indicators showing at the shoe center are clear signs the linings are at the end of their service life and should be replaced. Most fleets replace shoes sooner to stay within spec and avoid inspection issues.
What to look for:
- Lining thickness near ¼ inch (6.4 mm) on non-steer axles.
- Lining thickness near ⅛ inch (3.2 mm) or less on steer axles.
- Rivet heads or wear indicators showing at the shoe center.
- Uneven or patchy contact marks across the shoe face.
Cracked, Chipped, or Heat-Checked Linings
Heavy braking and high temperatures can cause small surface cracks — or heat checks — to form across the lining. Light heat checking is normal, but once cracks deepen or spread across the full width of the friction material, the shoe is considered out of service under CVSA criteria.
Cracked or missing material reduces the surface area that contacts the drum, which can lead to vibration, uneven braking, or accelerated wear on the remaining shoes. Even minor cracking can worsen quickly under heat and load, so linings showing any full-width cracks or loose sections should be replaced before returning the vehicle to service.
What to look for:
- Cracks that extend the full width of the friction surface.
- Cracks longer than 1.5 inches (38 mm) or voids deeper than 1/16 inch (1.6 mm).
- Missing or broken sections exposing rivets or bolt heads.
- Loose lining movement of 1/16 inch (1.6 mm) or more.
- Blue or dark discoloration indicating overheating or thermal fatigue.
Glazed or Polished Linings
A shiny or glass-like finish on the lining surface indicates glazing — usually caused by light, prolonged brake applications or excess heat. Glazed linings lose friction and can extend stopping distances. Bendix notes that glazed friction can lose up to 40 % of normal grip and should be replaced, not resurfaced.
What to look for:
- Smooth, reflective friction surface.
- Hard or slick texture on the lining.
- Squeal or reduced braking response during light applications.
Oil or Grease Contamination
When hub seals or wheel-end components leak, oil or grease can soak into the friction material. Contaminated linings are an out-of-service violation since they lose grip permanently and create uneven braking or smoke under heavy use. Because oil can’t be cleaned out of the lining, the only fix is replacement, along with repairing the source of the leak.
What to look for:
- Dark or oily patches on the lining surface.
- Burnt smell or visible smoke after braking.
- Wet residue on the shoe or drum interior.
Uneven Wear or Tapering
Uneven wear patterns usually mean something else in the foundation brake isn’t working right, such as a worn cam bushing, weak return spring, or misaligned hardware. The shoe will wear faster at one end, or one wheel on the axle may show heavier wear than the other. Without correcting the underlying cause, new shoes will wear unevenly the same way.
What to look for:
- One edge of the lining is significantly thinner than the other.
- Uneven wear between left and right shoes on the same axle.
- Shiny or dark spots indicating uneven contact with the drum.
Visual Defects and Drum Interaction Issues
Even when the linings and hardware appear to be in good shape, the wear pattern on the friction surface can reveal how well the shoes and drum are working together. Uneven contact, heat spots, or surface scoring usually point to drum condition problems — such as being out-of-round, glazed, or worn beyond spec. These issues can cause noise, vibration, or reduced braking consistency and will quickly wear down new shoes if the underlying cause isn’t corrected.
Leopard Spotting and Heat Marks
“Leopard spotting” refers to discolored or patchy marks on the lining or drum surface caused by uneven contact pressure or heat transfer. These hot spots develop when the drum and shoe surfaces no longer match evenly, allowing parts of the lining to overheat while others do very little work. If left unaddressed, the condition can harden the friction material and create chatter or pulling during braking.
What to look for:
- Discolored or dark circular marks on the lining or drum.
- Patches of uneven wear across the friction surface.
- Vibration or shuddering when the brakes are applied.
Raised Drum Edges and Grooving
As drums wear, a small ridge can form around the outer lip where the shoe doesn’t make full contact. Over time, this ridge prevents the shoe from seating evenly, leading to partial contact, noise, or reduced braking surface. Deep grooves in the drum can cause the same issue and may leave matching score marks on the lining. Meritor recommends replacing or machining drums that exceed wear limits (+0.120 in) or show ridge formation.
What to look for:
- Noticeable ridge around the outer edge of the drum.
- Deep or uneven grooves visible inside the drum surface.
- Scoring or matching wear lines on the shoe face.
Edge Chipping and Surface Crumbling
When a drum is out of round or the shoe doesn’t match its arc, stress builds along the edges of the friction material. This can cause the lining to chip, flake, or crumble near the ends. Minor edge wear is normal, but missing chunks that expose rivets or bolt heads are considered defective and will place the brake out of service under CVSA inspection criteria.
What to look for:
- Chipped or missing lining material along the edges.
- Exposed rivets, bolts, or large voids near the friction edge.
- Uneven chamfers or cracking where the shoe meets the drum.
Audible and Performance Clues
Not every brake shoe problem takes a visual inspection to be discovered. Some of the most useful warning signs are the sounds and sensations drivers notice during daily operation. Noise, pull, or vibration under braking can all point to shoe or lining issues that need to be checked during the next service.
Squealing or Grinding
Many brake shoes are designed with wear indicators that make a high-pitched squeal once the lining nears its minimum thickness. That sound is an early signal to schedule an inspection before the shoe wears down to metal. If the squeal turns into a grinding or scraping noise, the friction material is likely gone and the rivets are contacting the drum. Continued use at that point can damage the drum surface.
What to listen for:
- Consistent squeal from one wheel end during light braking.
- Metallic grinding or scraping noise that worsens with pedal pressure.
- Changes in tone or volume as the brakes heat up.
Vibration or Pull
If the truck pulls to one side or the brake pedal vibrates, one or more shoes may not be applying evenly. This can be caused by uneven wear, contamination, or mechanical problems in the foundation brake components. These symptoms also appear when drums are scored, out of round, or when one wheel end is over-adjusted compared to the other.
What to watch for:
- Steering wheel movement or vibration under braking.
- Pulling to one side, especially on light stops.
- Uneven heat or odor at wheel ends after braking.
Brake Fade or Weak Braking Response
Brake fade happens when excessive heat reduces the friction between the lining and drum. It’s most common during long downhill grades, repeated stops, or when brakes are dragging slightly due to misadjustment. While fade itself is normal and temporary, the heat that causes it can harden, glaze, or crack the friction surface. Repeated fade cycles can also lead to drum scoring or out-of-round wear, both of which shorten shoe life.
What to watch for:
- Noticeable loss of braking force during repeated stops.
- Longer stopping distances on long grades or under heavy load.
- Hot smell or light smoke coming from a wheel end after braking.
Brake Dust, Smoke, and Odor
Brake dust and odors can also point to problems developing at the shoe. Excessive dark dust around a wheel end may signal rapid lining wear or contamination. A strong burning odor or visible smoke, on the other hand, usually means a brake is dragging or oil has reached the friction surface — both conditions that can quickly destroy the lining and place the brake out of service.
What to watch for:
- Heavy brake dust buildup around one wheel end.
- Burnt odor or visible smoke after braking.
- Signs of heat discoloration on the drum or hub face.
Brake Shoe Maintenance and Inspection Best Practices
Most issues from brake shoe damage can be avoided with consistent inspections and part replacement done on schedule. Shoes should always be replaced in matched axle sets to maintain even braking and prevent one side from overworking the other. When installing new shoes, check the drums, rollers, return springs, and bushings — worn hardware can quickly damage fresh linings.
Tracking wear by wheel position over time can also help spot issues early, such as a dragging brake or misadjusted slack adjuster. Replacing shoes before they reach minimum thickness and addressing the root cause of uneven wear keeps trucks braking smoothly, extends drum life, and reduces the risk of unplanned downtime.
Keeping Brake Shoes in Serviceable Shape
Brake shoe damage doesn’t happen overnight. It builds up through heat, wear, and small issues that go unnoticed until inspections catch them. Knowing what those signs look like, and addressing them before they reach the drum, keeps trucks braking safely and consistently.
Regular maintenance, matched replacements, and attention to early warning signs all go a long way toward preventing downtime and keeping your fleet inspection ready. For help identifying the right replacement shoes or lining kits for your application, search our site for cross references, or talk with our parts team to find the correct match for your truck or fleet.