AfterMarketNews Brake&Frontend BodyShopBusiness Counterman EngineBuilder Fleet Equipment ImportCar Motorcycle & Powersports News Servicio Automotriz Shop Owner Tire Review Tech Shop Tomorrow's Tech Underhood Service Speedville

Honda Civic: Failed PCMs And CAN System Diagnostics

It’s not unusual for me to get help requests through my e-mail. Sometimes it’s from working technicians, other times it’s from vehicle owners who can’t get their problems solved through professional repair shops. In early 2014, I received one...

Read more...

Servicing Mercedes-Benz AIRMATIC Suspensions

The Mercedes-Benz AIRMATIC suspension system was introduced in 1999 on the S-Class and has subsequently been used on the E-Class and most of the automaker’s SUVs. The system employs electronically controlled air springs that provide an ideal balance...

Read more...

Mazda: Performing Regular Undercar Maintenance

In this article, we’ll take a look at brake and undercar service on the Mazda vehicle lineup, with the footnote that even though this type of work ­becomes routine when you have a preventive maintenance mindset, good work habits from beginning to end...

Read more...

The Ins And Outs Of Sanders

Sanders are required tools in today’s collision repair shop. Body techs and painters rely upon them every day to achieve that perfect finish on your customers’ vehicles. Whether you’re prepping a panel for paint or removing imperfections before...

Read more...

Are You Regularly Maintaining Your Equipment?

Technicians who are idling because the welder won’t feed wire, the hydraulic ram won’t pull chains, the booth heater won’t heat or the air compressor won’t compress enough air is a costly mistake, as labor time is the most expensive thing in any...

Read more...

Celebrate 'Back To The Future' Day By Watching The Time Machine Get A 2015 Detail

    For many today is just another Wednesday, but for a lot of people it is more than just your average Wednesday, it is "Back to the Future" Day. It is a day that everyone who watched the cult classic trilogy Back to the Future recognizes...

Read more...

Solving Carbon Deposits In Direct Fuel Injection Engines

Symptom: Misfire codes, stumbling and suspicious fuel trim numbers. On a scan tool, the engine may show a loss in volumetric efficiency. The driver may complain about a loss of power, poor fuel economy and hard starts. Cause: Carbon deposits on...

Read more...

Using Your Oscilloscope: Current Ramp Test Ignition Coils

Regardless of design configuration, the role of the ignition coil is to multiply battery voltage into high voltage. Following Ohm’s law for the conversion of volts to amperes, oil-filled coils generally require 3 to 5 amperes of primary current...

Read more...

Serial Data Bus Diagnostics

Understanding The Function of Serial Data Buses If serial data buses did not exist, a wiring harness would have to be five times its normal size and use twice as many sensors to deliver the same level of functionality and safety we see in the modern...

Read more...


Home Brakes 7 Brake Myths Busted

Print Print Email Email

There are some myths about brake pads, rotors and hydraulics that need to be busted. These myths can hurt and hinder a technician’s ability to diagnose and solve some brake problems and customer concerns.

On the surface, some of these myths make sense. The logic can seem sound and explain a problem, but they do not resolve the real issues with a brake system.

A Rotor’s Minimum Thickness Specifications are Based on Heat
False: The discard or minimum thickness specification is based on travel of the caliper piston if the pads were worn to the backing plates.

If you had worn pads and a rotor below specification, there is a possibility the piston could start leaking and possibly become dislodged from the bore causing a failure of the brake system. Heat, warping and fading have nothing to do with discard specifications.  

Soft Pads and Hard Pads
False, with a pinch of engineering truth. The engineering term for measuring the hardness of brake pads is compressibility.

Engineers typically measure compressibility as a manufacturing quality control measurement and not as a performance measurement. Compressibility is an important characteristic and can influence pedal feel, but it has very little to do with noise, rotor wear and pulsation.

What the driver is experiencing is the type of friction (tribology) the friction material is using to stop a vehicle. A “hard pad” is a pad that is abrasive to the rotor. This could be classified as a semi-met pad. These types of pads can have very stable friction over a wide range of temperatures.

What a technician or customer think of as a “soft” pad is typically an organic or ceramic formulation. How these friction materials generate brake torque is by adhesion type of tribology. These friction materials leave or transfer a layer of friction material (transfer film or “seasoning”) on the rotor’s surface that some friction material companies claim can smooth out the rotor surface, thereby causing less excitation and noise at the friction coupling. Also, this transfer layer may not be as sensitive to heat induced brake torque variation. Some of these friction materials can be friendly to rotors.

Both of types of friction materials can be the same in terms of compressibility. Calling one material soft and one hard is not possible unless your shop has a $20,000 machine to measure the compressibility of the materials.

Compressibility can influence pedal feel, but only in extreme cases where the pad could be defective. What really influences pedal feel is the coefficient of friction of the brake pad.

Damaged Brake Hoses Can Cause Brakes to Drag
 False, with a dash of truth. The myth usually takes place on a vehicle where the brakes are stuck on at just one wheel. The technician tries just about every thing and eventually theorizes it is a restriction in the brake hose. 

Brake hoses can be damaged by road debris and some clamps. Stock brake hoses are typically two or three layers. All modern hoses have a stiff internal liner that is in contact with the fluid. The outer layers are typically a softer material designed to absorb impacts with road debris.
 
The myth typically states that the inner liner was damaged and created a flap or check valve in the line. This check valve prevents the pressure from releasing at the caliper. But, this has been know to happen older brake lines from the 1960s.

In theory, it does makes sense, but you have to ignore some facts. First, if this flap was created, it would not form a internalized flap. Chances are the entire liner would fail and the brake fluid would be up against the softer outer liner. This would make the hose bulge and eventually burst. 

Chances are the restriction could be  a stuck emergency brake, caliper slides or even a problem with the metering/combination valve. Also, many stuck brake problems are related to brake booster or meter/combination valve problems.

Wet Brake Rotors Increase Stopping Distances
 False: Remember when you were first learning to drive and some adult told you to tap the brake pedal after you drove through a puddle? In the days of drum brakes, this was good advice, but with disc brakes this piece of advice does not hold water.

If a vehicle is moving, water is thrown off the face of the rotor by centrifugal force. Any water on the pads is inconsequential.

Replacement Brake Pads are Regulated by the Government
False: There are no government regulations concerning brake pad performance.  

 

 

Brake Pads Need to Warm Up
 False: Street brake pads are designed to produce even brake torque even at very low temperatures. This is even true for exotic carbon ceramic brake systems on street-driven vehicles.

The exception for this myth is high performance racing pads that require some heat in the friction material to generate its highest coefficient of friction. Manufacturers of these pads will say that these pads should only be used for off-highway purposes.

Brake Pads Are The Source of All Brake Noise
 True & False: All brake pads do produce vibrations when they are applied. This happens on all brake systems. But, it is how the vibrations are transferred to the rest of the vehicle that will cause a driver to hear or not hear the noise. A brake pad is merely the a string on a guitar, it is up to the player or vehicle to decide how it sounds.

Humans have a limited range of hearing so the sound made by some brake pads might be unheard.

What can cause noise is a change of the friction material due to heat. A “consistent” friction material causes less vibrational excitation variation at the friction coupling by having consistent brake torque at environmental extremes of humidity and temperature (-40F to 500F).

Typically, high frequency noises come from the caliper, rotor or bracket. Low frequency noises, like growls, grunts and moans, can be caused by struts, knuckles or even the body structure.

The option for technicians are to isolate the pads with lubricants, shims and restoring the hardware to like-new condition. 

The following two tabs change content below.
Andrew Markel

Andrew Markel

Andrew Markel is the editor of Brake & Front End magazine. He has been with Babcox Media for 15 years. He is a technician and former service writer and holds several automotive certifications from ASE and ­aftermarket manufacturers. He can be reached at [email protected]
Andrew Markel

Latest posts by Andrew Markel (see all)

Latest articles from our other sites:

GF-6 Oil Specification: What It Means For Your Shop

The Obama Administration finalized fuel economy standards in 2012 designed to increase fuel efficiency standards to 54.5 mpg for passenger cars and light-truck applications by 2025. This push for greater...More

Hunter's Quick Check And Quick Tread Fully Integrated With AutoServe1

Hunter Engineering’s Quick Check and Quick Tread now fully integrate with the AutoServe1 digital vehicle inspection and customer communication system. According to AutoServe1, its product is one of...More

Registration Open for ETI’s 36th Tech Week

Since 1947, the Equipment and Tool Institute has been meeting with automakers in order to fulfill one of the association’s most important goals, which is to provide member companies an ongoing stream...More

STAR EnviroTech Sponsors U.S. Military Veteran Automotive Scholarship

STAR EnviroTech is working with the University of the Aftermarket Foundation (UAF) to fund a Military Veteran Automotive Scholarship. The scholarship is open to any active or honorably discharged...More

Continental Announces New VDO Xtreme LED Tachometer

Continental Commercial Vehicles & Aftermarket has announced the new VDO Xtreme LED Tachometer for street rod and hot rod enthusiasts. The company says it provides easy programmability, a top range...More

GM TPMS Tips

Shops should use a TPMS tool that can reset the sensor positions after rotation. There is a method in the owner’s manual to “match” the sensors that involves deflating a tire for eight seconds. On...More