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Failure Analysis
Signs of Unusual Wear
(DISCLAIMER: Before beginning, please note that not all brake complaints and problems can be solved by only brake shoe inspection. Common problems also occur as a result of high temperature issues, such as air, mechanical or friction imbalances. Any imbalance in one or a combination of all three will appear as a friction material issue. The necessity for inspecting and replacing all worn parts has become more critical with the advent of automatic slack adjusters and ABS.)When brake drums are removed, the brake lining should be inspected for signs of unusual or atypical wear. Common problems may arise as a result of ignoring hardware upkeep and s-cam bushings. These problems include but are not limited to: Bottom brake shoe worn more than the top shoe; Lead shoe blocks primary contact, with very little contact on the anchor block; Excessively noisy brakes.


Noisy Brake
Cam block, glazedAnchor block shows no contactRoller seat on lead shoe shows wear on high side
POTENTIAL ISSUE:Standard lining may be placed in an extremely oversized drum


High Temperatures
Resin BleachingBlisteringContinual Cracking, rivet-to-rivet the full width of the shoe
POTENTIAL ISSUE:Over-adjusted brake; Improper downhill braking procedure; Improper friction application

Bent Spider; Bent S-Cam Tube
Tapered wear along the side of the lining
POTENTIAL ISSUE:Poor Lining-to-Drum contact

Blistering & Flaking of the Brake Lining
Rust, obvious flaking of brake lining with 75% of the lining left
POTENTIAL ISSUE:Improper friction application

Excessive Center Wear on Brake Lining
n/a
POTENTIAL ISSUE:Friction torque level is insufficient for vehicle application

Lining Separation from Brake Shoe Table
Cracking at rivet
POTENTIAL ISSUE:Oversized drum; Previously lined on a stretch core

"Craters" in Brake Lining
Cracks or gauges missing in brake lining
POTENTIAL ISSUE:Oil-soaked brake lining

Poor Stopping Power/Noisy Brake
Grooved wear pattern
POTENTIAL ISSUE:Brake shoes that are placed in a grooved drum may take longer to seat and make good contact, or else make no contact at all
