You Brake It, You Bought It:
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1. eal June 2009 MOTOR 27 AVOIDING BRAKE SERVICE SURPRISES Electrical Connection Parking Brake Solenoid Photos amp screen captures Bob Pattengale The 2004 Audi A8 uses an electronic parking brake system The rear disc brake caliper left has an electronic motor attached to apply pressure to the brake pads The motor must be retracted using a scan tool before the caliper piston is depressed The system is activated by a switch right mounted in the console The advent of new braking technol ogy as well as fluid servicing systems and the appearance of hybrid vehicles are changing how some of these sys tems are serviced Let s take a look at a few examples Electronic Parking Brake System Vehicle manufacturers are looking for ways to reduce weight and enhance ve hicle safety systems One system that s seeing wider application is the electron ic parking brake system Audi began us ing this on the 2004 A8 and it s now standard on all 2009 Audi vehicles The electronic parking brake system uses a rear disc brake caliper that looks standard except for the solenoid assem bly attached to the back of the caliper The driver uses a switch on the center console to request parking brake en gagement This request is received by the electronic parking brake control module which then applies electrical current to the parking brake solenoid The control module determines the motor cutoff point by e2. do you consult the service manual prior to ser vicing a vehicle s brake system Are you the type who consults the service manual only when you get stuck or do you take the time to review repair procedures in advance Brake system service is one repair area often taken for granted M ost of us wouldnt hesitate to rack a ve hicle pull the wheels and begin performing a brake inspection or repair without any additional guidance We rely on our experience to alert us to potential problems but on some late model vehicles if you re not careful you might have a nasty surprise waiting for you during the repair D epending on how old you are you might remem ber seasoned technicians complaining about the transi tion from front drum brakes to front disc brakes or about the addition of rear disc brake systems can re member comments like What new tools am going to have to buy to repair these new systems Or Why do they have to complicate things In the early days you could repair virtually any brake system with four or five basic tools Did you find yourself making the same comments or complaints when you had to purchase a tool to de press the rear disc brake caliper piston by rotating the s an experienced service technician how often 26 MOTOR June 2009 By Bos PATTENGALE en proper procedures are overlooked or ignored mi brake service can make a quick transition from NBD to OMG Something as see
3. front brake pads This is be cause regenerative braking is used to help stop the vehicle Since regenera tive braking uses the hybrid electric mo tor to slow the vehicle s front wheels front brake pad wear is reduced The opposite is true on most vehi cles The front brake pads wear at ap proximately twice the rate of the rear M ost shops perform some type of pre ventive maintenance inspections and make recommendations for future ser vices Understanding the difference be tween conventional and hybrid braking systems is important if you want to esti mate when the rear brake pads might need service Flushing the Brake System Brake fluid flushing is a maintenance item now commonly performed in most shops Again the question is Should you perform this service without con sulting the service manual By now your answer should be No but let s take a look at the following example You just completed a brake service on a 2004 Chevy Silverado 1500 4WD which included a complete brake fluid replacement You ve performed this same service on other vehicles with no known issues After flushing the brake fluid on this vehicle the brake pedal feels spongy Your first thought is that maybe one of the calipers has some trapped air so you perform the bleed procedure again with the same re sults a spongy pedal What should you do now try again The obvious next step is to check the service manual In this case you ll f
4. these features One fairly new feature is ABS Freeze Frame Data which is similar to an OBD II freeze frame capture Whenever an ABS trouble code is detected the ABS control unit stores information at the time of the event This data can be used to determine possible causes or conditions when the trouble code was stored The screen capture on this page is from a 2007 Dodge Durango with a C101F Right Front Wheel Speed Comparative Performance trouble code This code sets when the right front wheel speed sensor reading is different from the readings of the other sensors when the vehicle speed is above 25 mph As you can see the right front wheel speed sensor is 71 mph and the left front wheel speed sensor is 30 mph Obviously the right front wheel speed sensor and or circuit needs to be inspected for potential issues The next time you have an ABS trouble code on a late model vehicle check to see if freeze frame data is available H opefully by now you get the pic ture Brake system service is not as simple as it used to be If you re not 100 sure about how a system is ser viced refer to the service manual It M This article can be found online at www motormagazine com June 2009 MOTOR 31
5. The pis ton moves a little then stops What now Well you think maybe the piston is stuck or cocked a little so you apply more pressure Then you hear something snap This is when the swearing begins What just happened You just dam aged the parking brake motor assembly which might cost you as much as 800 for one caliper This is where you finally consult the service manual for the prop er procedure for servicing this system The proper procedure involves using a scan tool or electronic device to retract the motor Once the motor is retracted you can depress the caliper piston in the conventional manner The screen cap tures on page 30 show part of the scan tool functional test required to properly retract the parking brake motor to ser vice this system Once the brake service is complete the scan tool is used to properly adjust the parking brake motor Hybrid Brake Pad Replacement You may never have thought that a scan tool would be required to replace a few brake pads But this is the future of brake service And we re not done let s look at another example a Ford Es cape You re thinking Piece of cake I ve serviced hundreds of Fords You rack the vehicle pull the wheels perform your brake inspection and recommend a complete brake service As you re making notes on the work order and performing the underhood vehicle in spection you re reminded that this is a Ford E scape H ybrid In the back of your mind y
6. can tool The diagram on this page shows the typical hydraulic passages in an ABS system The red passages represent brake fluid flow during normal braking If you were performing a basic brake fluid flushing process the fresh brake fluid would travel through these pas sages But what about the yellow pas sages In this example the old brake fluid in the yellow passages would not be replaced If you were performing an automated brake fluid service with a Some vehicle manufacturers have begun using freeze frame captures for ABS trouble codes The ABS mod ule captures information from vari ous Components and sensors to help the technician determine what part of the system might be at fault This capture from a 2007 Dodge Durango shows that the right front wheel speed sensor reading does not match those of the other three sensors scan tool the pump and solenoids would be cycled to allow for complete fluid replacement Brake fluid flushing is now a com mon practice The question is How would you know if an automated process is available The service manual will provide the correct pro cedure ABS Diagnostics Up to this point we ve focused primarily on brake service issues But what about diagnostics ABS diagnostics requires the use of a scan tool with a variety of features The scan tool must be able to retrieve trouble codes display data and perform various system tests M ost scan tools with ABS coverage offer
7. ind a long description on how to perform the H ydraulic Brake System Bleeding Pressure using a pressure bleeder Af ter reading this and following all the procedures you get to Step 26 which states If the brake pedal feels spongy perform the following steps Step 1 nspect the brake system for external leaks Step 2 Using a scan tool perform the ABS Automated Bleed procedure to remove any air that may have been Illustration courtesy of the University of Toyota Flushing the brake fluid has become a common vehicle service This illustration shows a typical Toyota ABS hydraulic system If you performed this service without the aid of a scan tool the only fluid that would be replaced is shown in red The old fluid will still be present in the yellow sections of the system trapped in the Brake Pedal M odulator Valve The ABS Automated Bleed Proce dure is 16 steps long and includes a pos sible repeat of the pressure bleeding process The key point is Knowing in ad vance that you might need to perform the Automated Bleed Procedure if the pedal is soongy You would have wasted valuable time attempting to repeat the pressure bleeding process Also what if your scan tool doesn t have this feature It would be a good idea to check your Current scan tool in advance If your scan tool doesn t have this Special Function don t perform this service What s the benefit of performing a brake bleeding procedure with a s
8. mingly simple as installing a set of pads could ruin shop profits or cause injury piston into the caliper This new tool is required for vehicles with parking brake systems that me chanically adjusted the rear disc brake caliper pis ton Vehicle braking systems have changed over the years but they remained very simple for the most part and up until 10 years ago still required very ba sic tools The addition of antilock braking systems ABS became a very big concern and many of us at tended training sessions to learn how to handle poten tial problems This was a big leap for many technicians because now electronics were involved in mechanical amp systems The basic brake system now included ABS control modules wheel speed sensors and electrically operated hydraulic actuators Technicians who never needed or wanted to use a scan tool now needed one for some basic services The scan tool is now an essen tial part of brake service The good news or bad news depending on your perspective is that antilock braking systems don t fail very often and in most cases the basic service can be performed without the use of a scan tool or other unique procedures Up until a few years ago the pri mary use for a scan tool was for checking ABS codes and bleeding the brakes following a hydraulic module replacement F or the most part that s still the case iter Images rry phot ratio Photoillust
9. ou wonder if there s any thing unusual about this vehicle Your only service on this vehicle is brakes and you just finished a complete visual in spection including master cylinder and hydraulic control assembly and nothing looked different about the braking sys tem This looks like a standard braking system with antilock brakes so you de cide to move forward The job is approved so you dig In without consulting the service manual The calipers are loose and you re get ting ready to machine the rotors The ta Te ee a ee ee ee ed Solacbon of required funcion Centr wit gt gt LT iming r jLeemurt Hop 1 ES Til sensor zero position compensation Basic setting brake lathe is across the shop and you re surprised by what happens next With out warning the caliper pistons shoot out of the calipers What just happened here No one touched the vehicle the key was not even in the ignition and as a normal precaution you placed the keys on your workbench The vehicle decided to per form a random system check and when the brake system pressurized there was nothing to hold the caliper pistons in place I m guessing most of us would be shocked at this turn of events L et s take a look at what the service manual rec ommends Step 1 With the vehicle in N eutral position it on a hoist NOTE The following steps must be taken to prevent the accumulator from charging and pressurizing the brake system Ste
10. p 2 D isconnect the battery Step 3 Remove the battery junction box BJB fuses 24 50A and 31 50A Step 4 Service the brakes in the normal manner Would you have thought to discon nect the battery for a brake service on this vehicle F ord technicians say you can also use the F ord factory scan tool to disengage the braking system asked more than a half dozen F ord dealer techs and they were evenly split some used the scan tool and others disconnected the bat tery The bottom line is you need to perform one of the above tasks Again don t assume anything you must look up the proper repair procedure One interesting note about the F ord Escape H ybrid is that the rear brake 30 MOTOR June 2009 Continue with gt gt 1 Sofety spoc e sysiom Do noi Perform test step whilsi driving During test switch on groan angine OFF do not press brake relosse parking brake Brake lining rapakement sieg 1 The parking brake system on the Audi A8 is controlled by a separate control module These images taken from the Bosch Cantina Wih FS Control motors actuaied Lew oneal Feb Ciel pel KTS 570 scan tool tae perigee Lin replecamn show part of the j control vsti carers ina process of Peg peartieny br va Lim neppteceem retracting the parking brake motor prior to brake pad replacement pads wear at approximately twice the rate of the
11. valuating the motors power consumption In other words the control module monitors the amperage used to apply pressure and cuts power once the amperage reaches approximately 16 amps One interesting feature If the park ing brake has not been used during the last 620 mi 1000km the control mod ule automatically adjusts the parking brake The parking brake adjustment is critical for the DriveAssist feature on manual transmission vehicles The park 28 MOTOR June 2009 ing brake Is automatically applied based on vehicle tilt angle accelerator pedal position clutch pedal position and clutch pedal movement speed It s re leased when the driver moves from braking to acceleration Imagine you re servicing this vehicle for the first time Would you begin the service right away relying on experi ence or would you consult a service manual first What you decide to do will make the difference between a good repair and a big mistake Let s look at this service In this example you decide to jump into the service without instruction from the service manual The caliper is easy to remove basically remove two bolts and the caliper slides off The brake pads are a straightforward removal process too You inspect the caliper and determine its reusable The next step for most technicians would be to depress the Caliper piston so you pull out your trusty brake caliper piston depresser and begin applying pressure to the piston
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