AfterMarketNews AfterMarketNews Auto Care Pro AutoCareCareerHub 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

No More Free Tire ­Rotations!

Tire rotation is a cornerstone of vehicle preventive maintenance and tire longevity. It is a well-proven fact that tire tread life can be greatly enhanced by regular and timely tire rotation. During rotation, each tire and wheel is ­removed from...

Read more...

ASE G1: How To Measure Cold Cranking Amps, Reserve Capacity

The ASE G1 test contains 55 scored, job-related questions, 15% of which will concern electrical maintenance and repairs. From the ASE G1 study guide, you will need to know how to: • Perform battery tests (load and capacitance); ­determine needed...

Read more...

ASE A5: Brake Fluid And Bleeding Sequence

The ASE A5 Test includes a portion on brake fluid, bleeding, flushing and leak testing. You must know how to: • Diagnose poor stopping, pulling, dragging, or incorrect pedal travel caused by problems in the brake fluid; determine needed repairs. •...

Read more...

When Timing Is Everything: A Look At The 2.5L, 2.0L Powerplants

Last month, we looked at the timing chain setup on the Audi 3.2L engine and saw how a lack of oil changes can adversely affect the tensioners and cause engine failure. We’ve also seen similar issues with the timing chain setups on the 2.5L 5-cylinder...

Read more...

Modern Charging Systems: Cover All The Bases During the Diagnostic Process

To quote a familiar situation: “My customer’s car is now on its third alternator in six months and my jobber store refuses to ­warranty a fourth.” In other words, the parts supplier believes that an underlying problem is causing these alternators...

Read more...

Audi Fuel System: MIL On/Multiple Low Fuel Pressure DTCs

Due to fuel intrusion into the low-pressure ­system fuel pressure sensor (G410), a false signal may be sent to the controller, resulting in a reading that is out of tolerance. Model: 2007 Audi A4 Sedan V6-3.2L Scenario: The MIL is on and one or...

Read more...

Redline Detection Seeks Nominations for 2nd Annual Redline Rock Star Performance Award

Redline Detection is encouraging anyone who works with, or knows, a talented technician to nominate him or her for the second annual Redline Rock Star Performance Award. The award recognizes a technician for their commitment to family, community and...

Read more...

Automotive Lift Institute (ALI) Elects 2015 Board

Jerome Lentz of Challenger Lifts (Louisville, Ky.) has been elected chairman of the Automotive Lift Institute (ALI) Board of Directors for 2015. Voting took place at ALI’s annual membership meeting Nov. 3 in Las Vegas. Lentz’s 2015 term will be...

Read more...

Top 5 Tools: John Forro, AST, Automotive Service Technology in Hinckley, OH

John Forro AST, Automotive Service Technology Hinckley, OH ALLDATA Information System: I use this system daily for researching labor pricing, wiring schematics, circuit descriptions, torque specs, etc. One doesn’t need to memorize all the information...

Read more...

Must-Read TPMS Technical Service Bulletins

Here’s a rundown of the top technical service bulletins related to TPMS. These TSBs should be analyzed by every technician that services TPMS. Audi TSB Number: 4413382034445/1 Models: 2010-’14 A4/S4, A5/S5 and Q5 Summary: This TSB addresses TPMS...

Read more...

Ford Reflash: Setting Up Your PC

You’ve just finished up a job on a Ford vehicle, and you’re about to try and start it up. However, it needs programmed first. You’ve decided to use a J2534 tool, but there are certain things you’ll need to consider ­before purchasing that subscription...

Read more...

Fuel Line Replacement: The Why and How

If you live in a state that doesn’t get snow, you can stop reading right now. If you live in the Snow Belt, you are about a month away from snow and ice. It’s not the adverse driving conditions that should scare you or your customers, it’s...

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 is an ASE Certified Technician and former service writer, and he brings this practical knowledge to the Brake & Front End team as editor.

Latest posts by Andrew Markel (see all)

Latest articles from our other sites:

Hannay Reels N500 Series Provides Efficient Handling

Hannay Reels N500 Series high-pressure, low-maintenance spring rewind reel is designed for efficient hose handling in applications such as hydraulics, air/water, and chassis grease for all machine and...More

Beacon Offers Portable Electric Work Heater

The Beacon BPES series of electric portable work heaters are designed to be a safer alternative to heaters that operate off of propane or kerosene. There is no flame or odor emitted by the unit, though...More

When Timing Is Everything: A Look At The 2.5L, 2.0L Powerplants

Last month, we looked at the timing chain setup on the Audi 3.2L engine and saw how a lack of oil changes can adversely affect the tensioners and cause engine failure. We’ve also seen similar issues...More

Modern Charging Systems: Cover All The Bases During the Diagnostic Process

To quote a familiar situation: “My customer’s car is now on its third alternator in six months and my jobber store refuses to ­warranty a fourth.” In other words, the parts supplier believes...More

Hannay Reels N500 Series Provides Efficient Handling

Hannay Reels N500 Series high-pressure, low-maintenance spring rewind reel is designed for efficient hose handling in applications such as hydraulics, air/water, and chassis grease for all machine and...More

Beacon Offers Portable Electric Work Heater

The Beacon BPES series of electric portable work heaters are designed to be a safer alternative to heaters that operate off of propane or kerosene. There is no flame or odor emitted by the unit, though...More

Inspection TIps For Chain-Driven Water Pumps

Automakers are always trying to remove items from the accessory drive belt. This improves the efficiency of the engine and can extend the life of the belt. But where do you put the water pump? Some...More

Must-Read TPMS Technical Service Bulletins

Here’s a rundown of the top technical service bulletins related to TPMS. These TSBs should be analyzed by every technician that services TPMS. Audi TSB Number: 4413382034445/1 Models: 2010-’14 A4/S4,...More