Glazed Brakes

Glazed brakes are a friction problem, not simply an adjustment problem. On a commercial truck, the brake lining or pad must create enough friction against the drum or rotor to convert vehicle motion into heat and slow the vehicle. When the friction surface becomes hardened, polished, oil-soaked, or heat-damaged, the brake may still move when applied, and the pushrod stroke may still measure within limits, but the brake may not create the stopping force the driver expects.

That is what makes glazing different from ordinary brake fade. Brake fade is usually a temporary heat-related loss of braking effectiveness during or shortly after heavy brake use. As the brakes cool, some braking performance may return. Glazing is different because it changes the friction surface itself. The lining can become polished, hardened, or contaminated so that the brake continues to underperform even after the wheel end cools. Crash Forensics describes glazing as a hard crust on the lining surface that reduces friction at the brake’s friction surface.¹

The most common causes of glazing are:

Haldex warns that brake linings should be inspected for grease or oil, that oil- or grease-soaked brake shoes should not be reused, and that grease or oil on friction material can cause the lining to glaze and “not do its share of the braking.”²

The practical problem is that a truck with glazed brakes may not look like a truck with no brakes. The brake chamber may apply. The slack adjuster may move. The lining may still have thickness. The issue is whether the hardened or contaminated friction surface can generate braking force under load. That is why glazing belongs in crash investigations involving long stopping distances, rear-end collisions, intersection impacts, downgrade events, or claims that the driver “braked but could not stop.”

Why Glazing Matters in Heavy Truck Stopping Distance

Large trucks already require long stopping distances compared with passenger vehicles. In comments submitted during NHTSA’s truck tractor stopping-distance rulemaking, Advocates for Highway and Auto Safety noted NHTSA’s recognition that heavy truck stopping distances were considerably greater than passenger-vehicle stopping distances and that large trucks take about twice the distance to stop even during panic braking.³ That background matters because a reduction in friction at one or more wheel ends can lengthen a stopping distance that is already unforgiving.

Federal rules focus on brake function, brake condition, and brake performance:

• Section 393.48 requires brakes with which a vehicle is equipped to be operative.⁴
• Section 393.47 addresses brake actuators, slack adjusters, brake lining and pad thickness, and pushrod stroke limits.⁵
• Section 393.52 sets brake performance requirements, including stopping-distance and braking-force requirements for commercial motor vehicles.⁶

Those rules should be read together. A brake system does not become safe merely because a chamber moves and a lining is thick enough. The system must produce stopping force. That distinction is central to glazed-brake cases because glazing affects friction quality. A lining can be thick enough to avoid a minimum-thickness violation but still fail to create expected braking force because its surface has been hardened, polished, overheated, or contaminated.

Performance-based brake testing (“PBBT”) helps explain the difference. CVSA’s performance-based brake tester materials explain that visual inspection can evaluate component condition and adjustment, but actual brake force output cannot be determined from visual inspection alone.⁷ CVSA states that performance-based brake testers measure brake force and weight at each wheel, calculate total vehicle brake force, and compare it against total vehicle weight; U.S. federal regulations and the North American Standard Out-of-Service Criteria use a minimum braking efficiency threshold of 43.5%.⁸

That does not mean every glazed-brake investigation requires a performance-based brake tester. It means investigators should not stop at pushrod stroke. Stroke, adjustment, and lining thickness answer one set of questions. Glazing, contamination, friction quality, and brake force answer another.

How Brake Linings Become Glazed

Glazing usually develops through heat, contamination, or improper bedding of friction material. Heat can polish or harden the lining surface. Oil or grease can soak into the lining, then bake onto the friction surface during braking. Improper burnishing after a brake job can prevent the lining and drum from establishing the correct contact pattern. Light dragging applications or low-pressure braking can also create surface conditions that look shiny or mirror-like rather than properly conditioned.

Meritor’s brake drum troubleshooting guide identifies “polished or glazed drums” as drums with a mirror-like shine and lists causes including low-pressure braking and linings that are not aggressive enough or not OEM-approved.⁹ The same guide discusses hot spotting and heat-related drum conditions associated with slow burnishing, light dragging stops, brake drag, and non-OEM-approved linings.¹⁰

Burnishing matters because new linings do not reach full performance simply because they were installed. Meritor’s cam brake inspection guidance instructs technicians to road test to burnish new brake linings when required before returning a vehicle to service, then inspect the brake components and perform final brake adjustment.¹¹ A Freightliner service bulletin involving Meritor steer axle drum brake squeal similarly states that, after the burnishing procedure, there should be no brake noise and the brakes should have good stopping ability.¹²

Contamination is another major pathway. Wheel seal leaks, hub oil leaks, excess grease, and failed seals can put lubricant onto the drum or lining. Once the lining is saturated, cleaning the surface may not restore the friction material. Fleet Equipment, citing WABCO guidance, states that "burned, glazed, or oil-contaminated pads must immediately be replaced.”¹³

The common theme is that glazing is usually visible if someone looks at the friction surface. A shiny, glassy, polished, burned, or contaminated lining is not a hidden electronic fault. It is a maintenance condition. The question is whether the carrier’s inspections were detailed enough to find it.

Brake Defect Numbers Show Why Lining Condition Matters

There does not appear to be a clean national annual count for crashes caused specifically by glazed brake linings. The available numbers are broader, but they are still important. FMCSA’s Large Truck Crash Causation Study reported that brake problems were coded for almost 30% of trucks in the study, compared with about 5% of passenger vehicles.¹⁴

FMCSA’s LTCCS Analysis Series also discusses Michigan FACT post-crash inspection data involving 407 large trucks.

In that dataset of inspected large trucks:

• Inspectors identified brake problems in 32.7%,
• Some violation in 66.1%, and
• At least one out-of-service item in 35.1%.¹⁵

Those figures do not isolate glazing, but they show why brake condition remains central in post-crash truck inspections.

Crash-risk research points in the same direction. A 2017 study of interstate large trucks found that out-of-service brake violations tripled crash risk, while any out-of-service vehicle violation increased crash risk by 362%.¹⁶ IIHS summarizes large-truck research by reporting that brake defects were found in 42% of crash-involved trucks investigated in one North Carolina study and that out-of-service brake defects tripled crash risk.¹⁷

Roadside inspection data also show that lining condition is not theoretical.

The FMCSA MCMIS 2023 national violation report lists:¹⁸

• 2,806,452 inspections, 4,705,324 total violations, and 881,947 out-of-service violations.
• 14,575 violations for “Inadequate brakes for safe stopping — Brake Lining condition,” including 5,826 out-of-service violations.¹⁹
• 50,470 violations for “Inoperative/defective brakes,” including 9,403 out-of-service violations, and 49,564 violations where defective brakes equaled or exceeded 20% of the service brakes on the vehicle or combination, including 49,532 out-of-service violations²⁰

CVSA’s brake-focused inspection results provide more detail on lining and pad condition.

During 2024 Brake Safety Week, inspectors²¹:

During CVSA’s 2024 Brake Safety Day, inspectors:

• Conducted 4,898 inspections in one day.
• Placed 570 vehicles out of service for brake-related critical inspection item violations.
• Identified 185 brake lining or pad violations, including 62 contamination violations.²²

What NTSB Investigations Show About Hidden Brake-Lining Defects

NTSB’s Chesterfield, New Jersey school bus and roll-off truck investigation is one of the clearest examples of why investigators should examine brake friction surfaces. The NTSB vehicle factors report states that investigators examined major mechanical systems, including steering, braking, and suspension systems, and documented damage and anomalies.²³ The report also reviewed maintenance records and prior annual inspection reports,²⁴ along with supporting photographs, and removed several brake system components from the truck for additional examination.²⁵

The truck’s brake findings were significant. NTSB documented a cracked brake pad,²⁶ a loose brake pad lining, and oil or grease contamination at the rear axle.²⁷ In the most relevant finding for glazed brakes, investigators found that the right side axle #4 brake components were contaminated with grease and/or oil.²⁸

The brake pads appeared saturated with grease and/or oil and had a partially glazed area that appeared to be heated and dried grease and/or oil. The friction surface of the brake drum was also coated with grease and/or oil and had a similar partially glazed area.²⁹

NTSB treated that condition as a defective lining condition under CVSA criteria, making the right side of axle #4 a defective brake.³⁰ The report’s photograph list specifically identifies images of grease/oil contamination, grease/oil saturated and glazed brake pads, and a grease/oil saturated and glazed inside friction surface of the brake drum.³¹

The same report shows why records matter. NTSB obtained the last three annual vehicle inspection reports,³² more than three months of driver vehicle inspection reports, and more than three years of maintenance records.³³ The 2009 annual inspection report indicated that the service brakes needed repair and that repairs were completed the same date; later annual inspection reports noted no defects,³⁴ and 39 days of DVIRs from October 2011 through February 2012 noted no defects.³⁵

That record pattern is important. A lack of driver-reported defects does not prove that the brake linings were healthy. Glazing and contamination may require wheel-end inspection, brake-component removal, photographs, and friction-surface evaluation. The case illustrates why service records, annual inspections, wheel-seal repairs, brake job records, and post-crash photographs become central when a crash involves stopping-distance questions.

Why Glazed Brakes Can Be Missed by Standard Checks

Roadside brake inspections often emphasize brake adjustment, air leaks, chamber condition, lining thickness, missing components, and pushrod stroke. Those checks are important. They catch many dangerous defects. But they do not always measure friction.

A glazed lining can be misleading because the brake may not be “out of adjustment” in the ordinary sense. The pushrod may stay within stroke limits, the chamber may apply, and the shoe may move toward the drum. But if the lining surface is polished, oil-soaked, or heat-hardened, the brake may not produce normal torque. That distinction is why CVSA’s PBBT brochure is useful. It explains that visual inspection cannot determine actual brake force output.³⁶

The same issue matters after a brake job. A carrier may produce records showing new linings were installed, but new parts alone do not answer whether the brakes were properly burnished, adjusted, inspected, and returned to service with adequate stopping ability. Meritor’s guidance requiring road testing and burnishing after relining, when required, helps establish what competent service should include.³⁷

In crash litigation, this means the inspection should not end with “the brakes were in adjustment.”

Discovery and Litigation Evidence in Glazed-Brake Cases

Glazed brake claims usually turn on maintenance evidence.

The key records include:

• Brake service invoices
• Brake shoe and lining replacement records
• Wheel seal repairs
• Hub oil leak records
• Drum replacement or machining records
• Brake adjustment records
• Annual inspection forms
• DVIRs
• Roadside inspection reports
• Photographs of the wheel ends

If the crash involved a long stopping distance, investigators should also request:

• ECM data
• ABS data
• Brake application data
• Dash-camera footage
• Event recorder data
• Telematics
• Load records
• Grade and roadway data
• Post-crash inspection measurements

The most important question is whether the carrier had a chance to find the condition before the crash.

Glazing from contamination often follows a wheel-end leak or grease problem. Glazing from improper burnishing often follows recent brake work. Glazing from overheating may follow brake drag, repeated hard braking, driver complaints, or prior downhill overheating events. Each pathway should leave some record if the carrier’s maintenance system is functioning.

Visual evidence is especially powerful. Photographs of polished drums, shiny lining surfaces, burned areas, oil saturation, grease deposits, loose lining, or cracked friction material can explain why a brake underperformed even when adjustment measurements looked acceptable. The NTSB Chesterfield vehicle factors report is a useful model because it combined component inspection, photographs, maintenance records³⁸, DVIRs, and testing of removed components.³⁹

The difference between brake fade and glazed brakes also matters in expert analysis.

A truck can have brakes that move but do not stop well. Glazed brakes are one reason. They turn the investigation away from the simple question of whether the brakes applied and toward the more important question: whether the friction surfaces could actually create the stopping force the truck needed.

Sources

• [1] Crash Forensics, "Brake Failure Analysis,".
• [2] Haldex, "Recommendations for Complete Brake Maintenance," Form No. L20273 (rev. June 2007),.
• [3] Advocates for Highway and Auto Safety, Comments to the National Highway Traffic Safety Administration, Docket No. NHTSA-2005-21462, "Federal Motor Vehicle Safety Standards; Air Brake Systems; Truck Tractor Stopping Distance" (Apr. 10, 2006),.
• [4] 49 C.F.R. § 393.48, "Brakes to Be Operative,".
• [5] 49 C.F.R. § 393.47, "Brake Actuators, Slack Adjusters, Linings/Pads and Drums/Rotors,".
• [6] 49 C.F.R. § 393.52, "Brake Performance,".
• [7] Commercial Vehicle Safety Alliance, "Understanding Performance-Based Brake Testers" (brochure),.
• [8] Commercial Vehicle Safety Alliance, "Performance-Based Brake Testers (PBBT)," Operation Airbrake,.
• [9] Meritor, Inc., "Brake Drum Failure Analysis" (troubleshooting guide),.
• [10] Id.
• [11] Meritor, Inc., "Inspecting Commercial Vehicle Foundation Cam Brake Systems," TP-1363 (rev. July 2013),.
• [12] Freightliner, Service Bulletin 42-078, "Meritor Steer Axle Drum Brake Squeal" (July 29, 2020),.
• [13] Fleet Equipment Magazine, "Check Your Brakes: Putting a Stop to Brake-Related CSA Issues" (quoting Jon Morrison, President, WABCO Americas),.
• [14] Federal Motor Carrier Safety Administration & National Highway Traffic Safety Administration, "Report to Congress on the Large Truck Crash Causation Study" (Mar. 2006),.
• [15] Federal Motor Carrier Safety Administration, "Large Truck Crash Causation Study (LTCCS) Analysis Series: Using LTCCS Data for Statistical Analyses of Crash Risk" (Jan. 2006),.
• [16] Teoh, E.R., Carter, D.L., Smith, S., & McCartt, A.T., "Crash Risk Factors for Interstate Large Trucks in North Carolina," Journal of Safety Research 62 (2017): 13–21,.
• [17] Insurance Institute for Highway Safety, "Large Trucks" (research area overview),.
• [18] Arnold & Itkin LLP, "Analysis of FMCSA Motor Carrier Management Information System (MCMIS) Inspection and Violation Data, Calendar Year 2023" (data obtained directly from FMCSA and on file with the firm; not independently accessible via public URL).
• [19] Id.
• [20] Id.
• [21] Commercial Vehicle Safety Alliance, "CVSA Releases 2024 Brake Safety Week Results" (2024),.
• [22] Commercial Vehicle Safety Alliance, "More Than 500 Commercial Motor Vehicles Removed from North American Roadways in One Day Due to Brake Violations" (2024 Brake Safety Day results),.
• [23] National Transportation Safety Board, School Bus and Truck Collision at Intersection Near Chesterfield, New Jersey, February 16, 2012, Highway Accident Report NTSB/HAR-13/01 (adopted July 23, 2013),.
• [24] Id.
• [25] Arnold & Itkin LLP, Vehicle Factors Group Chairman’s Factual Report, NTSB Docket No. HWY12MH007 (Chesterfield, New Jersey investigation) (obtained from the NTSB public docket and on file with the firm; not independently accessible via a stable public URL).
• [26] Arnold & Itkin LLP, Vehicle Factors Group Chairman’s Factual Report, NTSB Docket No. HWY12MH007 (Chesterfield, New Jersey investigation) (obtained from the NTSB public docket and on file with the firm; not independently accessible via a stable public URL). (Note: this document describes a void in the edge of a brake pad lining; the final Highway Accident Report classifies this as a defective lining condition without using the word "cracked.")
• [27] National Transportation Safety Board, School Bus and Truck Collision at Intersection Near Chesterfield, New Jersey, February 16, 2012, Highway Accident Report NTSB/HAR-13/01 (adopted July 23, 2013),.
• [28] Id.
• [29] Arnold & Itkin LLP, Vehicle Factors Group Chairman’s Factual Report, NTSB Docket No. HWY12MH007 (Chesterfield, New Jersey investigation) (obtained from the NTSB public docket and on file with the firm; not independently accessible via a stable public URL).
• [30] National Transportation Safety Board, School Bus and Truck Collision at Intersection Near Chesterfield, New Jersey, February 16, 2012, Highway Accident Report NTSB/HAR-13/01 (adopted July 23, 2013),.
• [31] Arnold & Itkin LLP, Vehicle Factors Group Chairman’s Factual Report, NTSB Docket No. HWY12MH007 (Chesterfield, New Jersey investigation) (obtained from the NTSB public docket and on file with the firm; not independently accessible via a stable public URL).
• [32] National Transportation Safety Board, School Bus and Truck Collision at Intersection Near Chesterfield, New Jersey, February 16, 2012, Highway Accident Report NTSB/HAR-13/01 (adopted July 23, 2013),.
• [33] Arnold & Itkin LLP, Vehicle Factors Group Chairman’s Factual Report, NTSB Docket No. HWY12MH007 (Chesterfield, New Jersey investigation) (obtained from the NTSB public docket and on file with the firm; not independently accessible via a stable public URL).
• [34] National Transportation Safety Board, School Bus and Truck Collision at Intersection Near Chesterfield, New Jersey, February 16, 2012, Highway Accident Report NTSB/HAR-13/01 (adopted July 23, 2013),.
• [35] Arnold & Itkin LLP, Vehicle Factors Group Chairman’s Factual Report, NTSB Docket No. HWY12MH007 (Chesterfield, New Jersey investigation) (obtained from the NTSB public docket and on file with the firm; not independently accessible via a stable public URL).
• [36] Commercial Vehicle Safety Alliance, "Understanding Performance-Based Brake Testers" (brochure), supra note 7,.
• [37] Meritor, Inc., "Inspecting Commercial Vehicle Foundation Cam Brake Systems," TP-1363, supra note 11,.
• [38] National Transportation Safety Board, School Bus and Truck Collision at Intersection Near Chesterfield, New Jersey, February 16, 2012, Highway Accident Report NTSB/HAR-13/01 (adopted July 23, 2013), (supra note 23).
• [39] Arnold & Itkin LLP, Vehicle Factors Group Chairman’s Factual Report, NTSB Docket No. HWY12MH007 (Chesterfield, New Jersey investigation) (obtained from the NTSB public docket and on file with the firm; not independently accessible via a stable public URL). (supra note 25).