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