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    FRONT CALIPER ADAPTER ON GM "W" BODY BRAKE SYSTEMS

We receive many calls regarding General Motors "W" Body brake problems. These include poor stopping, premature front pad wear, hard pedal feel and premature rotor wear. We are now getting calls on one or both front calipers contacting the inner circumference of the front wheel. This results in thumping, grinding or vibration when the brakes are applied. Although the symptoms listed above seem to suggest a front brake problem, you will probably find that the vehicles experiencing one or more of these problems are equipped with rear disc brakes.

The cause of these symptoms is frozen rear caliper sleeves. These sleeves will not allow the caliper movement necessary to apply the outboard brake pads to the rotors to become a supporting part of the total brake system. The lack of full rear brake function causes the front brakes to do more vehicle braking than they were originally designed to do. This causes undo stress on all associated front caliper parts and mountings.

The problem of caliper contact with the inner portion of the front wheels is caused by the upper caliper adapter mounting hole becoming oval shaped allowing the caliper assembly to be forced outward, away from the rotor axis.

Repeated braking with poor rear brake assist overcomes the clamping force of the adapter bolts that go through the front strut flange. These bolts have a torque specification of 148 ft. lb.. The strut flange is not strong enough to stop adapter movement when the front brakes operate under these conditions.

The correction for this symptom is to thoroughly inspect the rear calipers for proper sleeve movement and rebuild or replace as needed. Then service the front brakes and front suspension as listed below.

Replace front strut housing.

Check front rotors for run out due to overheating.

Check front pads for excessive wear and/or glazing.

Replace front caliper hardware.

Replace front calipers if there is any indication the piston seal has been damaged due to overheating.

Unless both rear calipers are replaced with units that contain updated sleeves and hardware expect continuing problems of this nature to occur.

Synopsis Courtsey of BMC 
Tech Tip
(TT980301)

  SERVICE SOLUTIONS FOR ANTI LOCK BRAKE SYSTEMS

Maintenance and repair work on vehicles equipped with anti lock brake systems (ABS) represent significant profit and service opportunities for most shops.  Unfortunately ABS service can be confusing due to the complexity of the systems and the sheer number of system suppliers.  However, ABS does not have to stand for "Absolutely Bewildering Situation."  In fact, most repairs to ABS-equipped cars involve only the standard hydraulic and mechanical braking systems that most repair technicians already know.  And, although there are numerous ABS systems in use today, they all function in a similar way using similar parts.  Since there are differences between systems, it is best to always check the manufacturer's recommendations for each procedure.

Ten years ago, when ABS first appeared on cars, it was a system for preventing wheel lockup and skidding.  Today's systems include traction control to prevent wheel spinning during acceleration.  The popularity of ABS is growing.  The system is available on many car models and, by the year 2000, it is expected that all U.S. manufactured cars will have the system.  By March 1, 1999 it will even be required on all midrange straight trucks using hydraulic brake systems.

ABS improves driving safety because it modulates hydraulic pressure better than any pedal pumping human - it stops cars in the shortest distance possible.  In addition, it stops cars in as straight a line as possible while allowing drivers to steer if necessary while under maximum braking.  The system works by inserting a computer controlled hydraulic mechanism into the hydraulic lines that transfers pressure to calipers and wheel cylinders.  The computer uses real-time information from onboard sensors and braking data from its memory to evaluate the situation and send control signals to the hydraulic control device.  Hydraulic pressure is reduced at any wheel that is about to lock-up.  The result is that the wheel regains traction.

Though ABS is relatively new, the rest of the brake system is not.  The overall system - shoes, pads, wheel cylinders, calipers and assorted hardware - works the same way it always did.  Experience has shown that maintaining and repairing these traditional components correctly takes care of most problems.

Many warning lights are triggered by non-anti-lock components.  Problems in the regular brakes can cause ABS problems.  The needed repairs are often straightforward and involve worn or mismatched pads;  worn linings or grease on linings;  a bad rotor surface;  low brake fluid;  or a bad alternator or battery.

Though a number of manufacturers produce ABS systems today, they all fall into one of two categories;  integral and non integral systems.  Integral systems use uniquely designed parts that combine the functions of the control module, hydraulic modulator, master cylinder and brake booster into a single unit.  Non integral systems us a traditional master cylinder, conventional brake booster, and separate control module and hydraulic modulator components.  It's important to recognize the difference because the hydraulic fluid is under tremendous pressure in an integral system, which means certain safety precautions from the manufacturer must be observed.

Getting used to ABS systems has been a challenge for many car owners.  For example, a vehicle with four wheel ABS comes in to the shop and the complaint is clicking or clunking noises during acceleration following each ignition switch cycle.  There is also some feedback in the brake pedal.  The solutions is to do nothing . . . the sound and feedback, when present, is normal.  The system performs a self test called initialization during the first acceleration after each ignition switch cycle.  During this test, the modulator valves, solenoids and motors are operated and tested.  This typically occurs between 0 and 8 mph.  If any faults are found, the system disables itself.

Accurate diagnostics is important because ABS problems may appear to be breakdowns in the regular brake system.  A pedal drop condition, for example, may act like a bypassing master cylinder when it appears on trucks with Kelsey Hays rear anti- lock brakes (includes GM, Ford, Dodge, Issue, and Mazda models).  The problem may be caused by the dump valve in the ABS Modulator valve being held open slightly by debris.  Under normal braking conditions, the isolation valve is open and the dump valve is closed.  This allows pressure from the master cylinder to flow uninterrupted past the isolation and dump valves.  If debris prevents the dump valve from fully closing, some of the pressure is bled off into the accumulator, resulting in a bypass condition.  This fluid is returned to the system by accumulator spring pressure when the brake pedal is released.

Follow these steps when troubleshooting:

If the pedal drop reappears, the problem is in the modulator valve.  The modulator valve is not repairable and must be replaced as an entire assembly.

Once an ABS system has been opened up to replace a component, it might be a good time to change the brake fluid.  The brake fluid on most ABS systems readily absorb moisture when exposed to air.  Moisture in brake fluid leads to a lower boiling point of the fluid which can result in brake fade.  Moisture also causes corrosion in the bores of system components, eventually leading to premature seal wear, sticking valves and system failure.

In fact, most ABS systems failures can be traced to moisture contamination.  This can all be avoided with regular brake fluid flushing.  It is generally accepted in the industry that brake fluid should be changed every two years or 24,000 miles.  More frequent changes may be needed in severe service applications.  Always use the fluid specified by the manufacturer.  Currently, most are recommending either DOT 3 or DOT 4.  Be aware that silicone or DOT 5 is not recommended for ABS use since it often aerates when agitated.

What's next in ABS?  One emerging trend is enhanced stability control.  It was first offered by BMW in 1995 on 750iL and 850Ci models.  The system monitors how the car responds to the driver and road conditions.  If stability is in question, the system has several options to counteract the forces causing the vehicle to lose control or traction.  It can reduce engine power by backing off the throttle and/or retarding spark timing while simultaneously applying the brakes in any combination.  This all takes place in the blink of an eye and without driver input.

 

"10 Good Tip for Brake Service"

  1. Depressurize all integrated ABS systems before performing any work.  Failure to do so can result in physical injury.
  2. Refer to the manufacturer's recommendations before beginning ABS service work.
  3. Never over-tighten wheel lug nuts.  Bent rotor or brake drums may occur which can result in inaccurate wheel speed readings and brake pedal pulsation.  A properly calibrated torque wrench should always be used - air impact wrenches should not.  (True for non-ABS systems as well).
  4. Flush the entire brake system prior to installing a replacement unit.
  5. Always use recommended brake fluid from a sealed container.  Most manufacturers are currently recommending DOT3 or DOT4.
  6. Check each wheel sensor for proper resistance and air cap.
  7. Always disconnect negative battery cable when electrical components are disconnected.
  8. Inspect the entire brake system before road testing.
  9. Never use different sizes of tires.
  10. Be sure the brake system is properly bled. 

Synopsis Courtsey of Craig Gottfried
AUTOINC.  -  August 1997
(TT980601)

  BLEEDING BRAKES

WHY IS BLEEDING NECESSARY?
In order for the hydraulic brake system to function properly there must be a solid column of brake fluid throughout the entire system.  If air and/or moisture are present in the system, it can cause a "soft" or "spongy" feel to the pedal when applied.  Unlike a solid column of brake fluid, air is compressible and can allow excessive pedal travel and loss of available braking pressure when applying the brakes.  Moisture (water) in the fluid will boil (vaporize) when sufficiently heated causing the same conditions and will also contribute to corrosion of internal brake components.

Air and/or moisture can enter the system when repairs are made, or as brake components wear.  The rubber seals harden with age and heat and no longer flex properly.  When the seal relaxes, it no longer has the sealing capability to prevent air/moisture from entering the brake system.  Air and/or moisture can also enter through improperly threaded fittings.  Line fittings seal during pressure applications, but may allow air/moisture to enter when there is no pressure applied.  Typically this condition will not show any signs of external leakage.

Of most recent interest, based on testing conducted by GWR, Phoenix, major manufacturers and the Federal Government (NHTSA - National Highway Traffic and Safety Administration)... brake fluid contamination and thickening is now the most dangerous problem.  Brake fluid is one of the few automotive fluids that gets thicker when it wears and that can be dangerous because of the fine orifices (valves) that are now in our ABS equipped vehicles. The build up of contaminates (not water) can happen in as little as 6 months or 6,000 miles, if the driver is hard on the brakes or there is a heavy load being regularly carried (towing a trailer, driving in mountains, hauling cargo, tailgating, etc.)

The only way to be sure you are not getting into a dangerouse condition, while also maintaining your vehicle, is to test the level of brake fluid contamination at regular intervals. How do you do the test and determin when to flush?  Recently developed Strip-Dip, utilizing patented FASCAR technology, is the only system reccomended for detecting the level and growth rate of the contamination. Please review the technical information on Strip-Dip and the procedure for using it at:
http://www.gwrauto.com/stripdip.htm
 

METHODS OF BRAKE BLEEDING
Removal of air from the brake system is termed "bleeding the brakes".  There are several methods of recognized by professional technicians:

  1. Gravity Bleeding
  2. Stroke Bleeding
  3. Pressure Bleeding
  4. Vacuum Bleeding
  5. R.F.I. (Reverse Fluid Injection)

While one of these five methods of bleeding will work for most types of brake systems,, the newest technology, know as RFI, is the most effective at removing all air from the system.

When bleeding brakes on vehicles equipped with ABS systems, be sure you follow all applicable procedures and cautions outlined in the service manual for that application.
 

  1. GRAVITY BLEEDING
    Remove the master cylinder cover and open one or more of the bleeder screws to allow the brake fluid to flow out of the system by its own weight.  As the brake fluid drains out of the system it will also purge the air along with it.  When there are no more air bubbles in the escaping brake fluid and the fluid is clean, then the bleeder screws are closed.  (Note: It is important that the master cylinder reservoirs be kept full of fluid to prevent more air from being drawn into the system as it is being bled.)
  2. STROKE BLEEDING
    Have one person in the vehicle gently apply the brake pedal.  Have another person under the vehicle open and close the bleeder screws in the proper sequence.  Continue this process until the air has been purged.  It is really not recommended to "pump the pedal" as aeration of the fluid can easily occur.  If this method is used, the pedal should be depressed and released very slowly!  Additionally, try to not depress the pedal all the way to the floor while the fluid flows, before bleeder screw is closed.  (Note: Care must be taken when stroke bleeding the system.  The master cylinder seals can be damaged by forcing the seals over an area that has excessive rust and corrosion build up.  This build up is from moisture and other foreign matter which may be present in the brake system.  In the portion of the bore where the seal normally operates, it will stay clear of build up.  Where the seal has not traveled this foreign matter can cut or tear the seals if they are extended into this area during the bleeding process. To assure this type of damage does not occur, do not depress the pedal more than 3/4 of full pedal travel.  One method of assuring the pedal is not over stroked is to have the person in the vehicle place his/her left foot under the pedal.  However it is accomplished, the master cylinder must not be over stroked, or damage to the seal(s) may result.  It is also necessary for the person in the vehicle "stroking" the brake pedal to hold the pedal in the down position until the bleeder screw is closed to prevent air being drawn back into the system when the brake pedal is released.  Remember, do not rapidly pump the brake pedal )
     
  3. PRESSURE BLEEDING
    This is accomplished by utilizing a container with a diaphragm separating brake fluid from pressurized air.  This pressure is used to force brake fluid through the system.  The air is purged as the brake fluid flows out of the bleeder screws.  Open each bleeder screw in the proper sequence until there is no air present in the fluid.  With the correct adaptors and the proper bleeding sequence, this is usually the fastest method of bleeding a brake system. (Note: In pressure bleeding, use of the correct adaptor and the proper bleeding sequence eliminates the need to "stroke" the brake pedal.  This reduces the possibility of damage to the master cylinder.  Also remember that it may be necessary to utilize a metering valve hold off tool on some vehicles.  Follow service recommendations for specific applications.)
     
  4. VACUUM BLEEDING
    A vacuum is used to pull fluid through the system and trapped air theoretically flows along with it.  A tank utilizing a siphon is attached to the master cylinder reservoir to keep the system full as it is being bled.  The bleeder screws are then opened in sequence, while a vacuum draws out the old fluid and air.  The hose to the bleeder is clear plastic in order to see the air as it is purged.
     
  5. R.F.I. BLEEDING
    Reverse Fluid Injection is the latest technology and is now endorsed by many major manufactures and OEM's as a preferred method of bleeding their systems and vehicles.  You simply inject new brake fluid directly into the bleeder screws (at the bottom of vehicle) and allow the upward flow to catch and carry the air bubble to the reservoir (at the top of system.)  If you think about it, this makes sense because air rises in a liquid and that is the direction we push the new fluid with the RFI Injector Gun.  Please visit the section of our web site that fully explains this OEM Approved procedure and the injection guns that are now available... http://gwrauto.com/phoenix/phxinj.html

Another situation you may encounter....

Air trapped in the end of a master cylinder that is slightly higher than the secondary outlet will cause a constantly low and/or spongy pedal.  To eliminate this trapped air, remove the master cylinder and bench bleed, or raise the end of the vehicle that would make the master cylinder bore level prior to bleeding the system.

DIAGNOSING BLEEDING PROBLEM 

  1. No air or fluid will come out the opened bleeder screw
    A.  Bleeder screw plugged
    B.  Brake line, hose or valve damage
    C.  Metering valve tripped (if equipped)
    D.  Master cylinder outlet plugged
    E.  Air in master cylinder
     
  2. Low or spongy pedal after bleeding
    A.  Air in the system
    B.  Mechanically related
        1. Caliper or mount twisted or bent
        2. Excessive shoe to drum clearance
        3. Excessive pad to rotor clearance (e.g. rear disc)

Synopsis Courtesy of Raybestos (Division  of  Brake Parts Inc.)
Tech Stop Brake Service Bulletin
(TT980602)

    FLUSHING GLYCOL BASED BRAKE FLUIDS (DOT3, DOT 4)  

Brake fluid, like other fluids used in the automobile, needs to be changed at regular service intervals.  Because brake fluid deteriorates over time, it is recommended that it be changed every two years or 24,000 miles.  If the vehicle is operated in a humid climate, it may be necessary to change the fluid more often.

The most commonly used brake fluids, DOT 3 or DOT 4, are glycol based fluids that have the characteristic of being hydroscopic.  This means that brake fluid can absorb and retain moisture.  As moisture enters the brake system, it can then be dispersed throughout the entire system.  This prevents water from forming within the system and freezing or boiling before the fluid itself.

Moisture also reduces the brake fluid's lubricating capabilities and will dilute it's anti-corrosion additives.  This allows rust, corrosion and sediment to form within the hydraulic brake system.  The sediment migrates to the lowest points in the system during normal brake operation.  This results in the dirtiest, most contaminated fluid being found in the disc brake calipers and wheel cylinders.  Very often technicians performing basic relines, will simply push caliper pistons back into the caliper bores without opening the bleeder screws.  When this occurs, the old fluid and sediment from the caliper are both pushed back through the system to the master cylinder reservoir.  The dirt and sediment can cause restrictions in hydraulic components in the system.  This may result in uneven braking, drag or even premature disc pad wear.  On ABS equipped vehicles, the dirt and sediment can possibly cause a restriction or the modulator valves to stick resulting in an ABS light illumination.  It is strongly recommended, if the calipers are not being replaced, to open the bleeder screws before pushing the pistons back into the calipers.  This will prevent possible damage to hydraulic components within the brake system.

Brake fluid must maintain a stable viscosity throughout its operating temperature range.  It cannot get thicker as the ambient temperature goes down.  This would affect the fluid flow from the master cylinder to the wheels in sub-zero temperatures.  It also has to withstand the extremely high temperatures generated by the brakes during normal operation.  If brake fluid boils and turns to a gas rather than a solid column of fluid, it can no longer transmit the pressure needed from the master cylinder to apply the brakes.  Instead, the gas compresses and the brake pedal becomes spongy or travels to the floor when the brakes are applied, resulting in a brake system failure.  The boiling points of brake fluid are directly effected by the amount of moisture absorbed by the fluid.

The Federal Motor Vehicle Safety Standard 116 and the Society of Automotive Engineers specification SAE J1703 state that DOT 3 brake fluid must meet a minimum dry boiling point (new moisture free fluid) of 401 degrees Fahrenheit and a minimum wet boiling point (fluid containing 3 1/2% moisture) of 284 degrees Fahrenheit.  Brake fluid typically reaches its wet boiling point in approximately two years, thus requires changing.  Once it reaches its saturation point, brake fluid can no longer absorb moisture.  Then as additional moisture enters the system water forms that can cause corrosion, boiling or freezing.

    DOT 3   DOT 4
         
Dry Boiling Point   401F   446F
Wet Boiling Point   284F   311F

CAUTION: Use only the fluid specified by the O.E. manufacturer.  Petroleum based fluids such as engine oil, transmission fluid and power steering fluid are not compatible in a hydraulic brake system.  These products will cause the rubber components in the system to swell and cause hydraulic component failure in a short period of time.  To properly repair this condition, all components in the brake system that include rubber components must be rebuilt or replaced.  This would include the master cylinder, combination/proportioning valve, ABS hydraulic unit, brake hoses, wheel cylinders and/or calipers.  In addition the steel brake lines need to be flushed with denatured alcohol and then clean brake fluid to assure that no petroleum is left in the system.

Synopsis Courtesy of Raybestos (Division  of  Brake Parts Inc.)
Tech Stop Brake Service Bulletin
(TT980603)

    DISC BRAKE NOISE  

The most common complaint after disc brake service is noise.  Brake pads are often singled out as the cause.  The majority of brake noise is not generated by the friction material.  It is caused by vibration of a brake component that is not properly installed, insulated, secured or lubricated.  Improper insulating of the pads from the caliper housing or caliper piston is the most common cause of disc brake noise.  Follow recommended friction application for a specific vehicle.

Insulators:  Many late model applications now have a shim staked to the back of the disc brake pad as it is originally manufactured.  The disc pads on sliding, floating or fixed style calipers must use an insulator between the pad and/or the piston and caliper housing.  The most common insulator is either a spray or paste coating that is applied to the back of the pad prior to installation.  These coatings work OK, but over time they have a tendency to break down.  This allows metal to metal contact between the pad and either the caliper housing or the piston with noise as a result.  Another type of disc pad insulator is the shim.  Shims have evolved from a simple paper gasket type material to a woven fiberglass cloth impregnated with rubber or a thin wafer of steel coated with plastic.  These two types of second generation shims are far better at dampening noises but have one major draw back.  They have a tendency to shift or fall out during the life of the brake linings resulting in noise.  The latest generation of shims have corrected this problem.  The new shim design utilizes a Nitrile Phenolic dampening layer sandwiched in between two thin wafers of steel.  They have tabs to locate the shim properly on the disc pad backing plate and most importantly, have a heat activated adhesive to bond the shim to the back of the pad during initial use.  Disc brake shims should not be reused.

Lubrication:  Inspect the old linings for any shiny areas where the steel edge of the disc pad backing plate, anti-rattle clips or other metal disc hardware came in contact with the caliper housing, piston, or steering knuckle.  Clean these contact areas on the caliper housing and steering knuckle.  It may be necessary to use an abrasive such as emery cloth to remove heavy deposits of rust.  Apply a light coating of moly based brake lubricant at these same location(s).  (Note:  Do not use anti-seize, white lube or any other type of petroleum based lubricant, especially if it will come in contact with the rubber brake hardware components.  Only a moly lubricant is suitable for these metal to metal applications. GWR makes a special Moly based, extreme temperature lubricant for this purpose, please ask for part number GWR's Pastelub #90-2400.  On areas that come in contact with rubber we recommend our newest product Ceramlub #90-2800, it is extremly compatible with EPDM caliper bushing rubber.)

Hardware:  Install and lubricate new disc brake mounting hardware even if the old hardware appears in good shape.  The constant heating and cooling during the life of the previous lining can weaken the metal hardware components and make rubber parts lose their resiliency.  Weak hardware parts can cause noise and other related problems, by allowing excessive caliper/pad movement or binding.  Related problems include;  uneven and premature pad wear, overheating of pads and rotors, rotor warpage, pulling and poor stopping ability.

Rotors:  Existing rotors must be machined, if reused.  A coarse or rough surface finish will contribute to noise complaints and/or poor braking ability.  Once the rotor is machined, (Note: GWR recommends Round Brake Lathe Bits #65-0066), a non-directional surface finish procedure must be applied.  Using a sanding block with 120-150 grit sandpaper, hold it against the spinning brake rotor surface for approximately one minute per side.  Work the sanding block up and down, while applying a medium amount of pressure.(Note: GWR recommends our rotor honing tool, part number #65-0120 for the best possible crosshatch finishes).  Before installing the rotor, be sure to clean it thoroughly.  Wash it with soap and water (Note: GWR has developed a special soap for rotors, part #90-5000), then allow it to air dry or you can wipe it dry with paper towels.  If the rotor is not cleaned thoroughly, fine metal particles left over from the machining process can become imbedded into the new brake pads.  These metal particles can in turn cause noise after brake service.  Lathe operation and maintenance is crucial to obtaining a good surface finish.  Refer to the Raybestos Disc & Drum Brake Specifications Manual (3415R) for machining specifications.

Break in:  Repeated hard stopping or abusive driving should be avoided with new friction material.  Brake related noise can be caused by a number of  factors.  Attention to detail and utilization of the above mentioned service tips will minimize disc brake noises and reduce customer complaints.  It is normal under certain conditions to have a nominal amount disc brake noise.  Some OEM manufactures even state this in their factory issued technical service bulletins.

Synopsis Courtesy of Raybestos (Division  of  Brake Parts Inc.)
Tech Stop Brake Service Bulletin
(TT980604)

    CHARGING OR JUMP STARTING LATE MODEL VEHICLES
EQUIPPED WITH ANTI-LOCK BRAKES (ABS)

Condition:  It is possible to safely start or charge an discharged battery, however, certain steps must be taken to insure it is done properly.  ABS and other on-board computers can be damaged by voltage spikes and/or current surges.  To help prevent voltage spikes, manufacturers install diodes in the vehicle electrical systems.  Diodes perform well up to a certain voltage, but then fail.  If this happens, the high voltage is allowed to continue throughout the electrical system and can damage electrical components including the ABS computer module.  Manufacturers use fuses and fusible links to prevent, excessive current flow from overheating and damaging the wiring.  A current surge occurs when battery cables are connected to a good battery, battery charger/booster or when a wire is shorted to ground.  To prevent possible damage to any electrical system components when jump starting a vehicle adhere to the following safety precautions:

  1. Do not leave the ignition switch on at any time while connecting or disconnecting jumper or battery cables.  The resulting current surge, if allowed to travel past the ignition switch, can damage electrical components in the system.
  2. Do not attempt to jump start a vehicle that has totally dead battery.  Slow charge the battery first before trying to start.  If this is impractical disconnect the negative battery cable before fast charging.
  3. Use a second battery when jump starting a vehicle.  Portable gasoline powered boosters and 110 volt service garage type battery chargers produce higher than normal (13.5v - 14.7v) charging system voltage, when set on either fast charge or boost.  This voltage is enough to "over run" the diode and damage electrical components including the anti-lock control module.
  4. ABS systems can draw large amounts of current during an Anti-lock assisted stop and as the system goes through a self diagnostic check. Some ABS control modules will monitor charging system voltage to ensure the Anti-lock system has an adequate current supply.  Heavy current draw on a partially discharge battery could cause the engine to stumble/stall or illuminate the ABS light.  If this occurs allow the battery to charge sufficiently before restarting the engine.  The light will go out on it's own, although a trouble code may remain in the ABS control module memory for a predetermined number of drive cycles.

Synopsis Courtesy of Raybestos (Division  of  Brake Parts Inc.)
Tech Stop Brake Service Bulletin
(TT980605)
 

  FALSE WHEEL SPEED SENSOR CODES

Vehicles Involved:  All vehicles equipped with Anti-lock brakes.

When performing brake, suspension or drive train system diagnostics or service, it is possible to set a false diagnostic trouble code (DTC) if the wheel(s) are rotated with ignition switch on.  If a wheel speed sensor DTC is set, the system warning lamp will illuminate and the ABS computer will store the fault code.  NOTE:  Warning lamp illumination signifies that the computer has detected a system malfunction and that Anti-lock system is disabled.  The ABS warning lamp will remain illuminated until the speed sensor code is cleared from computer memory.  To clear a wheel speed sensor DTC from the ABS computer it may be necessary to use one of the following methods;  Cycle the ignition switch off and on, drive the vehicle over 20 mph, ground diagnostic test terminal in a particular sequence or use a scan tool.

Once the code has been cleared, the ABS warning lamp will remain off and the ABS is now operational.  On some systems the DTC(s) may remain stored in the history portion of the ABS computer.  These code(s) remain in computer memory until, either the vehicle has been driven a predetermined number of drive cycles or the vehicles ignition has been cycled a number of times.  On some systems a scan tool can be used to clear code(s) from history portion of the memory.

To eliminate the possibility of false wheel sensor codes during servicing, always ensure the ignition is in the off position prior to rotating the wheel(s).

Synopsis Courtesy of Raybestos (Division  of  Brake Parts Inc.)
Tech Stop Brake Service Bulletin
(TT980606)

  BRAKE  ROTOR  SERVICE  PROCEDURES

Vehicles Involved:  All Domestic and Import Vehicles

Condition:  Servicing a brake system with aftermarket friction material.

Diagnostic Procedure:  The technician must perform a visual inspection of the rotors.  The visual inspection allows the technician to evaluate the rotors to determine if machining will enhance the brake system performance and longevity.  The inspection criteria are as follows:

  1. The rotor must be free of excessive runout and parallelism.  Use a dial indicator to check the rotor for runout.  The maximum total indicated runout (TIR) used to be .004 inch (0.1mm), but new standards developed in late 2002 now ask for OEM factory production of less than .001 inch (0.025mm). Secondly, use a micrometer to measure rotor thickness at 5 different points around the circumference of the rotor.  The maximum thickness variation allowed is .0005 inch (.0125 mm).  (Note: GWR now has an inexpensive dial indicator tool available so everyone can perform this important check during a brake service, the part number is #65-7139 .) 
  2. The rotor surface must be free of excessive scoring, for example grooves deeper than .050 inch (1.2 mm).
  3. Bluing or hard spots on the rotor surface indicate the rotor was subjected to excessive heat.  Replacement of  these types of  rotors is a must.
  4. Replace the rotor if cracks are visible anywhere on the rotor.
  5. Please refer to "Machine To" and "Discard" dimensions to determine if machining is possible or replacement is required.
  6. If the rotor is machined, apply a light non-directional finish to the rotor surface using a flat rubber sanding block and 120-150 grit paper.  Be sure to change the paper on every single side, so the final grit remains the same across all four surfaces.  (Note: GWR recommends our rotor honing tool, part number #65-0120 for the best possible crosshatch finishes.  It reprofiles the trued surface so as to eliminate a jagged, pointed surface that cause heat during the burnish period.)
  7. Wash the rotor with soap and water and rinse to remove loose metal and sand paper particles from the rotor's surface.  (Note: GWR offer a specially formulated, soap for washing cast iron brake rotors, the part number is #90-5000.)

    Note: If undecided about resurfacing a rotor, go ahead and do it.  A smoother, truer rotor surface is less likely to cause noise problems or  brake pedal pulsation during braking.

Synopsis Courtesy of Raybestos (Division  of  Brake Parts Inc.)
Tech Stop Brake Service Bulletin
(TT980901)

  HYDRAULIC  SYSTEM  DIAGNOSTICS

Condition:  Brake pedal that is soft and spongy or sinking to the floor.

Diagnostic Procedure:  The following is a step by step method to quickly find possible reasons for the lack of a good brake pedal:

  1. Visually inspect the master cylinder for leaks and note the condition and level of fluid.
  2. Lift vehicle on hoist and remove the wheels.  Visually inspect the entire hydraulic portion of the brake system, and note any signs of leakage.
  3. If the vehicle is drum brake equipped, check for proper shoe to drum clearance and adjust if necessary.  If the vehicle is rear disc brake equipped, check for proper pad to rotor clearance and adjust if necessary.  Some vehicles may also need parking brake adjustment in order to obtain proper pad to rotor clearance.  *Test the brake pedal feel.  If adjustment did not correct pedal feel continue to the next step.

    *  On vehicles with power assisted brakes it is crucial that the engine be running to get an accurate indication of pedal feel.  On manual brakes it is not necessary to start the vehicle when checking for a good pedal. 

  4. Using the proper clamping tool (ie. GWR #65-0035), gently clamp all the rubber hydraulic hoses to approximately half of their normal diameter.  Do not crush the hose.  This will require 3, 4 or 6 clamps depending on type of hydraulic system routing.  *Apply the brake pedal.  If the pedal is high and firm, continue with step 5.  This indicates the master and any components in between it and the hose clamps could not be the cause of the pedal problem.  Those components, if equipped, include the pressure differential switch, ABS/Traction Control Valve assembly, combination valve, proportioning valve(s), metering valve and all connecting steel lines and fittings.  If the pedal is soft and spongy go to step 7.
  5. Follow the OEM recommended bleeding sequence.  This information can be found in the Raybestos "Hydraulic Brake System Bleeding Sequences" booklet #2767R or in the factory service manual.  Remove the hose clamp that  leads to the first wheel in the bleeding sequence.  Do not remove any of the other clamps at this time.  *Test the feel of the brake pedal.  A high and firm brake pedal indicates that this portion of the hydraulic system is not contributing to the low or soft pedal problem.  Reinstall the hose clamp.  A low pedal would indicate excessive mechanical movement or air in that portion of the system.  Bleed as necessary and recheck for proper pedal feel.  Once that portion of the hydraulic system is not contributing to the soft or spongy brake pedal reinstall the hose clamp.  If there is a mechanical reason for the soft or spongy pedal note problem and reinstall hose clamp. 
  6. Continue through the bleeding sequence.  Checking each portion of the hydraulic system independently from the others.  When any one of the clamps is removed and the brake pedal is soft, spongy or low, bleed or diagnose that individual portion of the system before continuing to the next portion.  After each portion of the system has been checked and only bleeding was necessary to get a firm pedal, remove all the hose clamps.  *Then test the brake pedal feel.  If the pedal is high and firm go to step 10.  If there is a mechanical reason for the low or soft pedal, then repairs would be necessary in order to correct the problem.
  7. If the pedal is soft, spongy or sinking with all the rubber hoses clamped then there is air in the hydraulic system above the hose clamps or a mechanical problem in one or more of the components mentioned in step 4.
  8. Remove the steel line(s) from the master cylinder and plug the port(s) with the suitable fitting(s) from the Raybestos master cylinder bench bleeding kit BSE 125.  Have an assistant apply the brake pedal approximately half way down as the fitting(s) that plug the port(s) to the master cylinder are loosened.  This will purge the air trapped behind the plug.  Then re-tighten the plug.  *Again check the feel of the brake pedal.  If the pedal is high, hard and firm the master cylinder is good (not bypassing internally) and does not contain trapped air.  Reconnect the line(s) to the master cylinder.  Have an assistant manually apply the pedal and loosen the line fitting(s) to purge the trapped air.  Then re-tighten the brake line fitting(s).  *Check the brake pedal.
  9. If the problem still exists, and the master and all components below the hose clamps are good, then the problem would be in between.  Work down from the master and plug the outlet side port of any component(s) in sequence until the cause is found.  Bleed the system again following the OEM recommended sequence.
  10. Fill the master cylinder reservoir to the proper level and test drive.

Synopsis Courtesy of Raybestos (Division  of  Brake Parts Inc.)
Tech Stop Brake Service Bulletin
(TT980902)

 

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