Brake Job Maintenance

Brembo high-performance rotor and cailper were considered but not selected

Brake Work Foundation Issues

Brake work can be simple to complex, easy to impossible, and is absolutely something that must be done correctly.  Your life and the life & well being of others rides on the integrity of the repair. 

This article will address some of the specific issues associated with how your editor did a recent brake pad and brake rotor replacement.  If you are not skilled, proficient, and have the proper tools then leave this to a professional. 

Failure is not an option!

A recent article addressed many technical aspects of brakes and provides a good foundation for reference associated with brake maintenance.

3 Steps In The Brake Job

Doing a brake job typically involves three steps: figure out what you need, get the parts, and install the parts. 

Depending on your level of mechanical talent and available facilities, tools, and equipment you may want to install the brake parts yourself or hire a professional.  As for determining what parts to get, you may or may-not turn that over to the professional brake installer.

Subject Vehicle

The brake work will be on a 2001 BMW X5 with the 4.4L engine.  This is a solid and fun vehicle that gets mediocre gas mileage.  It is also fairly heavy and generates a lot of brake dust on the front wheels with the OE (Original Equipment) type of brake pad.

What Do You Want Your Brakes To Do?

Before doing the brake job two issues were identified.  First was reduction or elimination of brake dust.  Second was the fact that the front rotors were worn and would need to be replaced as part of normal maintenance.

200 miles since the tire and wheel were washed

Internet research into owner comments about how their brake linings worked hot, cold, wet, dry, noise, pedal pressure and brake dust were reviewed.  There is no shortage of owner comments about brakes and after broad and focused researching of the subject decided that Akebono Euro ceramic pads were the best selection to address my highest concerns of safety and cleanliness or more specifically wet weather braking and brake dust.

OE Brembo rotors were selected

Brake Component Options

Brake rotors on the X5 are designed to wear away and are therefore, consumable.  OE brake rotors are by Brembo with vented rotors front and solid in the rear.  It was decided to replace both front and rears although only the front rotors were at the end of their service life.

BMW front and rear brake pads incorporate a rather simple but elegant brake wear indicator.  The small and inexpensive sensors attach in the pad and when the pad is about worn out the sensor is ground through which turns on the Brake Light on the instrument cluster.  One sensor is for the front axle and one sensor is for the rear axle.  It is not totally foolproof to eliminate the possibility of a destroyed rotor but if the system is balanced in braking force then the driver will be notified in advance of metal-to-metal contact.

Brembo cross drilled rotors for racing and aggressive street driving

Parts Availability

After determining that this brake job would include Akebono Euro ceramic pads matched to replacement OE Brembo rotors then the decision was where to source from?  Spending a few minutes with eBay Motors and searching for BMW X5 Brakes proved to be the right decision.  About 300 listings came up and I found a vendor that could provide the specific parts needed at a competitive price.  Replacement sensors were also ordered but were not needed.

It can be a real challenge when researching available components.  However, making this selection properly will ensure that the vehicle performance is consistent with the functional requirement and budget established.

Slotted rotors for racing or aggressive street driving

Replace Pads & Rotors

Cross-drilled & slotted

Changing the brake pads requires caliper removal.  Removal of the rotors is more challenging.  Rotors fit over the hub and after 70,000 miles and 7 years an acetylene torch (smoke wrench) was required to heat the rotors to expand the rotor and then application of a large hammer to break the bond between rotor and hub.  It is amazing what water and age can do to bond these components together.

Road Test

Brake pad identification

With the new brake parts installed the car drives great and brake dust is essentially eliminated.  This was a successful mechanical project. 

It is interesting to note that a great deal of time and effort were spent before actually performing the maintenance.  Good foundation work resulted in a technical outcome that was precisely as planned.  That type of outcome and work is something that you can take pride in!

Brake Pads & Friction Material

Brakes mechanically stop your vehicle. 

When you put your foot on the brake pedal, hydraulic pressure is transmitted through the brake lines and the pressure moves the piston which mechanically pushes the pad or lining material against the brake rotor or brake drum.

Brakes turn kinetic energy into heat. 

Applying the brakes causes a speed loss in the vehicle because of friction between the brake lining and rotor or drum.  Friction generates heat and repeated stops or high speed stops generate massive amounts of heat.  Finned brake rotors move air through the rotor to cool the rotor.  Wheels are bolted to the brake rotor and through conduction the wheel also dissipates heat from the brake rotor.

Brake friction materials 

also typically need to exhibit long life, resist corrosion, have low noise, and be cost effective.  From a driver’s standpoint the most important aspect is that the brakes stop the vehicle predictably and without problematic brake fade.

Organic brake material can be defined several ways such as: containing carbon, asbestos, nonasbestos, Kevlar, ceramic, and other natural materials that have been resin bonded into a friction material. 

Asbestos Brakes

was a great friction material at an affordable price that operated quietly.  Unfortunately, asbestos fibers can cause asbestosis which can lead to COPD, lung cancer or mesothelioma.  All of these bad medical conditions represent the reason that asbestos brake linings are essentially a thing of the past with limited application into the 1993 model year.

In the old days, compressed shop air was used to blow off brake parts creating a huge cloud of asbestos fibers as mormal routine for the auto mechanic.  When asbestos medical problems surfaced because of the Occupational Safety and Health Act of 1970, with OSHA Regulations that ultimately changed operational procedures in the automotive brake repair department and clutch disk department and gasket department.  A lot of asbestos went into automobiles and some of that asbestos can still be found in automobiles.  In the link above, and repeated here, is an excellent NIOSH report from 1989 dealing with Asbestosis Exposure in Automotive Brake Service.  If you have ever been exposed to this hazard or you have a particular interest in this topic then you should review the article.

Brake pads today

fall into many different categories and definitions including: Original Equipment or OE, semi-metalic, Premium, Non-Asbestos Organic (NAO), Low-Metallic NAO, and NAO Ceramic.  Society of Automotive Engineers, SAE J-866a defines how friction materials should be identified when the friciton material is tested according to SAE J-886. 

When you look at the edge of the brake  lining material it will have a two letter code that corresponds to the normal friction level and one letter that represents the hot friction level.  If you are really into brake pads for ultimate performance then you will want to become very familiar with J-886a.  If you have concerns about big truck air brake systems then you will need to reference the Maintenance Council of the American Trucking Association RP-628 which relates to the Federal Motor Vehicle Safety Standard (FMVSS) 121 test procedure.

Brake Material Selection

Establish specific performance characteristics, such as low dust and reasonable price, and then research available technology and information.  Internet research will likely help to answer your questions and provide detailed assessments from individuals using that product.

Historical research comparison will help the proper decision to be made.  Police vehicles lead a very demanding performance life and therefore police vehicles have significant research documents that are available for brake component decision making.

At the High Performance Driver Training Program brake life was about one to two weeks.  This same time frame is also applied to a typical New York City taxi because these cars can stay in service around the clock.

It is critical from a safety standpoint that brakes work reliably.  However, special performance characteristics and the type of various friction materials available make for a challenging choice of replacement brake components.  Brake rotors and drums wear out and these must be measured and inspected for condition.

Decision Point

From a basic decision the answer is OE.  From an advanced decision you will have to start your search at this point.  It is a challenging objective.

Post Crash Analysis For Unrestrained Occupants

Seat belts are an important part of the safety systems in cars.  To a trained investigator review of a Traffic Crash Report, site visit, and inspection of the vehicles can answer many questions about the technical nature of the impact.

In this analysis the objective is to provide a thorough identification of steps associated with arriving at impact speeds and assessment of seat belt usage for front and rear passengers.

Scale diagram Prepared

for Impact and Final Rest vehicle positions. Inspection of the crash site permitted final rest placement for the Mercury. Final rest position was not identified on the Crash Report and no specific evidence at the crash site permitted placement of the Honda at final rest. … Continue Reading

Motor Vehicle Accident Reconstruction & Biomechanical Physics – Part 3

Aerial Crush Photography 

On-site aerial photographs taken with the aid of a boom and perimeter grid capture collision data. This system has proven to be extremely useful in addressing collision dynamics.A brief synopsis of this method reveals its usefulness to the accident reconstructionist and biomechanical expert. 

Horizontal lines for the red car illustrate 1′ of interior crush to the impact side-bar beam in the door and 1.5′ of collapse in the vehicle roof structure.  Also, shown on the opposite side of the car is a general bowing of the vehicle structure showing how impact forces are transmitted throughout the vehicle. … Continue Reading

Motor Vehicle Accident Reconstruction & Biomechanical Physics – Part 2

Vehicle Data

Making a good physical inspeciton of a collision vehicle can provide much important information about impact severity and expected injuries.  These example photographs document chest and facial impact.   It is significant to note that the steering wheel is deformed more on the left side which indicates the relationship of Principle Direction Of Force or PDOF to the vehicle and the center of mass movent of the unrestrained driver. 

Close inspection for the inside of the windshield will often show evidence of hair and blood that can be recovered for further forensic analysis.  Documentation of impact evidence is very important, especially when the investigator has to deal with the old statement “the dead person was driving“! … Continue Reading

Motor Vehicle Accident Reconstruction & Biomechanical Physics – Part 1

Robert C. McElroy, Ph.D.

ABSTRACT — Accident reconstructionists rely on a wide range of methods to record and analyze motor vehicle accident information. This paper addresses contemporary methods of obtaining and analyzing collisions with emphasis on G force explanation for biomechanical analysis.

INTRODUCTION — Traffic accident reconstruction is the effort to determine, from whatever resources are available, how an accident happened. A traffic accident reconstructionist must be familiar with the application of a wide range of mathematics and specialized aspects of vehicle technology. Because of the wide range of knowledge required by the accident reconstructionist, voluntary certification is available through the Accreditation Commission for Traffic Accident Reconstruction. ACTAR certification includes education, work experience, and successful completion of a comprehensive examination.

Unrestrained driver upper torso impacts steering wheel and lower extremities impacts lower dash

MATHEMATICS FOUNDATION —

Mathematics are at the core of traffic accident reconstruction. Many different equations are used to determine different aspects of an accident. Sir Isaac Newton developed three mathematical laws of motion which provide the foundation for traffic accident reconstruction.

In Newton’s first law of motion an important property of matter appears. It is known as inertia, that property of matter by which an object maintains a constant velocity in the absence of an unbalanced external force. When an automobile is suddenly stopped, the passengers obey Newton’s first law and continue in their motion with constant velocity until some external force changes their state of motion. Seat belts in a automobile can provide such an external force which is much preferred to that exerted by the windshield or dashboard. Another statement is the following: A body at rest remains at rest, and a body in motion remains in motion with constant velocity along the same straight line unless acted upon by some outside force. … Continue Reading