| ABS/ESC & REPLACEMENT BRAKE PADS | | | | Article adapted from an original article by Thomas Hall.
Reproduced by courtesy of Brake & Front End | | | At most workshops, the person ordering brake pads is given the choice of a several levels of brake pads.
The good, better and best marketing is sorted out by price and brand rather than solid engineering data. Sometimes the mechanic has no choice when the choice is dictated by the reseller who only stocks certain brands | | | In today’s brake friction market, many resellers put margin before technology and performance on the parts ordering screen. This can leave the person ordering the pads in a difficult position when his goal is to select the right brake pad for the safety of his customers. Also, what effects can a replacement brake pad have on the ABS, traction and stability systems? | | | | ABS, TCS and ESC | Everybody who installs or orders brake pads should be asking themselves the following questions: | | | | Will installing replacement brake pads from any source impact the performance of the safety systems that use brake control? | | | | Also, are all these new safety systems capable of adapting to different brake pads? | | | | To understand these questions and evaluate the potential answers, it is first important to have a basic understanding of the various chassis control systems the “wheel brakes” support and what are the operating principles and control strategies they employ. There are essentially five general chassis control systems available on today’s vehicles. On some vehicles they are standard and on others they are options available to the car buyer. | | | The Five Chassis Control Systems | | ABS (Anti-Lock Brake System) | | | | This is the basis for all the other technologies. The primary function of ABS is to manage the slip (lockup tendency in engineering speak) of each tyre and control the amount of slip each tyre is allowed. This is done to optimize the ability of the tyre to generate longitudinal tyre forces and lateral tyre forces. This is engineering jargon which means how much stopping power and cornering power the tyre, and ultimately the vehicle, can generate. In other words, the system allows the driver to brake and turn at the same time. | | | | EBD (Electronic Brake Force Distribution) is the next extension of ABS | | | | This system replaces the function of the traditional proportioning valve and manages the front to rear brake balance of the vehicle across all vehicle loading conditions and road surface conditions | | | TCS (Traction Control System) is essentially ABS in reverse | | | | TCS works to allow the tyre to provide the maximum longitudinal tractive force during acceleration and also match the engine output to the level the road surface can absorb | | | ESC (Electronic Stability Control) | | | | This technology takes the path the vehicle is really travelling and compares this to where the driver really wants to go. If the two do not match, the vehicle is either understeering or oversteering. Once one of these conditions is identified, the brake system is activated to provide a rotation force on the vehicle to get it back on track. It is kind of like sticking a paddle in the water of a canoe to force a turn. | | | | Roll Stability Control (RSC) | | | The most recent technology emerging on some vehicles.
This system evaluates the tendency of a vehicle to roll over and once the onset of a roll is identified, the wheels on one side of the vehicle are heavily braked in order to reduce the amount of lateral adhesion. The goal is essentially to put the vehicle into a side slide to prevent the role tendency. | | | The control algorithms for all these systems are extremely sophisticated and contain literally thousands of individual parameters that are tuned specifically to the particular vehicle line and brake system used on the vehicle. These parameters are developed, refined and tuned on a large variety of manoeuvres, speeds and road conditions. | | | | It is certainly reasonable to wonder, after all the work to develop a fully integrated set of systems, what happens when a different set of friction material is put on the car, or more commonly, on one axle of the car during service? | | | | To understand the potential effects, we must go a bit deeper into how these systems generally operate. In all of these systems, the computer controller (the brains of the system) is monitoring the vehicle watching for an indication that an undesirable operating condition starts to appear. | | | | These systems closely monitor individual wheel speeds, vehicle deceleration, engine output, steering wheel angle, yaw rate, lateral acceleration and roll rate among many other secondary indicators. The controller uses all of this information to determine very precisely what the vehicle is doing compared to the desired behaviour of the driver. Then a corrective action plan is determined. The brain then commands a “torque change” (or “torque” in engineering shorthand) to the desired wheel brake. The system can not directly control torque. It can only control hydraulic pressure. | | | The desired correction may be a torque increase, decrease or hold. An individual torque command is developed for each wheel independently. The hydraulic pressure in the brake system is multiplied by the friction level of the pad resulting in a torque being applied to the wheel. | | | | Torque Confusion | | | | The system, based on all the tuning and teaching that was used to develop the system, assumes that for a given pressure command, a given torque correction will result. | | | | Remember it is torque that ultimately creates the desired vehicle reaction. By changing the pads to a material that has a different friction value, you have changed half the equation the system is counting on. | | | | As a result, the system will not get the torque reaction it expects for an optimum result. All of these systems operate on what is called a feedback control principle. In simple terms, this means the system calculates its best estimate of the required amount of correction and applies it. It then watches to see if that estimate was effective. | | | If it sees that it did not get the job done, it calculates another correction and applies again. This cycle continues throughout the event. By the way, the system is checking its progress at the rate of approximately 100 times each second and employing corrective actions perhaps around 10-15 times a second in multiple directions. | | | | When the friction value changes, which it will most certainly do with different friction material, the system will not get to the best correction as quickly as it was capable of when it had all of the parts it was expecting. In most cases, the system will learn and correct for the “error” the new pads have introduced. It just will take more tries to get there and take longer. This results in reduced efficiency by some measurable factor. | | | The systems will still operate and still provide substantial improvements in vehicle handling control and safety vs. not having them. They are highly adaptable, but they just won’t be as perfect as they once were. In most cases, this will be very difficult, if not impossible, to detect at the driver seat. | | | If you were to measure the true performance of the vehicle by things like stopping distance, amount of steering correction, amount of pedal feedback and more complicated things like yaw gains and manoeuvre entry speeds, you could expect to find measurable degradation under many manoeuvres. | | | Since the system is generally very good at minimizing these effects, it would be easy to be convinced that this is of no consequence and that you should not consider this as part of your buying decision when it comes to selection of brake replacement. | | | The ability to “copy” a friction material’s characteristics is a very difficult task under the best of circumstances. All service technicians should consider that the OEMs, the friction suppliers to OEM (like FMP the makers of Bendix) and developers of these systems have invested thousand of hours by some really smart and dedicated people and spent millions of dollars to tune these systems to their maximum capability and insure they work in absolute harmony with the rest of the vehicle. | | | | While this is done in some pretty obscure and unfriendly environments at times, it is all done to ensure maximum performance and control in the blizzard, torrential downpour or when the dog jumps in front of your customer’s car. Any decision to compromise this balance should be given careful consideration. As a general guideline, we would offer the following few thoughts: | | | | Always choose a high quality replacement pad that mirrors the original friction characteristics, like Bendix. Bendix pads are designed in the largest friction laboratory in the Southern Hemisphere and are designed for Australian road conditions. | | | | If you chose to not use high-quality replacement pad like Bendix, always chose a material with the same friction rating. (EE, FF) etc. and change it on all four wheels together. This will at least ensure that the braking ratio from front-to-rear is maintained as much as possible. | | | | Never replace only the Rear Brakes with a pad that has a higher friction level than what is specified for the vehicle. This will increase the amount of rear braking and increase the potential for a rear over brake condition under some road surface and loading conditions. A brand like Bendix has researched friction and worked with the OEMs to define the best friction for the vehicle and the application of the vehicle. Some of the cheaper pads on the market may have a ‘one size fits all‘ approach which can be detrimental to the safety of the driver. These cheaper pads are not designed to ‘sync’ with the electronics that are built in to your customer’s vehicle. | | | | In the modern vehicle, the wheel brake is challenged to contribute to a great many vehicle driving conditions extending way beyond just stopping the car. The friction material is a very key element in this. To maintain the optimum performance, it is important to understand the implications of the choices that are being offered to consumers and help them make an educated decision. | | | We recommend you check the Bendix Brake Pad Application Guide for details of what brake pads to recommend to your customer. | |
| DISC/DRUM | | MACHINING & CLEANING | | | |
| VARIOUS STAGES OF WEAR | | OF DISC BRAKES & SHOES | | | | Problem | Description | Pad Completely Worn Out
 | The bare metal backing plate is exposed with friction material entirely worn off. When the brake is applied, the metal surface of the backing plate is pressed against the surface of the rotor causing not only damage and excessive wear but triggers a high-pitch squeal.
Brake efficiency is reduced and can result in brake failure. The damaged rotor discs may need to be replaced. To avoid this condition, brake pad thickness should be checked regularly (at least once a year) and worn pads replaced when the thickness is reduced to 20-30% of original pad thickness. |  | Pad Surface Chipped
 | The surface of the brake pad exhibits cavities and voids descriptiond by low-grade raw materials and poor technology production processes. These may description noise problems and result in a longer stopping distance as the total friction surface is reduced which in turn accelerates friction wear.
To avoid this condition, it is recommended to choose Bendix friction materials which are manufactured using only high-grade components and assembled using the latest in friction materials technology and strict quality assurance processes. | | "Burnished" Friction Surface
 | Pad surface is charred showing dark traces descriptiond by abuse of the friction material, either due to overload or as a result of excessive speed braking instances. This state may also be descriptiond by a low-quality material or by a low, unsuitable friction rating neither matching vehicle nor driving style. The burnished pads will also generate noise issues and extend the stopping distance.
This condition can be avoided by selecting a friction material matching individual application and driving habits. | | Slippery, Shiny Surface
 | The surface exhibits shiny, circular traces which may be descriptiond by low-quality raw materials used in the manufacturing process. For a period of time brake efficiency is reduced, extending the stopping distance and causing noise problems. This condition can also occur after frequent, low-pedal-pressure brake applications. To ensure maximum brake efficiency the installation of Bendix high-quality disc brake pads are recommended. | | Bonded Brake Pads
 | Backing plates had been reused and bonded with friction material (pucks) using low technology, inferior adhesive agents and low-quality friction materials. The initial cost-saving brake job is unsafe and can result in puck separation and instant, total brake failure. Used backing plates should not be reused. Only complete and new assemblies of brake pads manufactured under strict quality assurance control, such as Bendix, should be used.
| | Hard Pedal Feel
 | Friction materials may contain metallic fibres to increase friction and shorten stopping distance, suitable for high speed driving and heavy duty applications. Brake pads made from semi-metallic materials are usually more expensive and brakes work best in the higher temperature range. Pedal feel is positive but may be harder than with NAO materials. | | Rotor Pick-up
 | Metal particles are embedded in the friction surface descriptiond by accumulation (rotor pick-up) of metal dust from lower grade metal rotor disc. This in turn wears the rotors excessively and increases stopping distance.
Deep grooves can found on rotor surface causing high-pitch squeal. | | Drum Lining Burnish
 | Dark, shiny traces on lining friction surface descriptiond by excessive lining thickness or installation of low-quality shoes. Also, incorrect adjustment or installation may description uneven wear and excessive temperature build-up. The use of high-quality brake shoes and installation by quality brake service fitters is recommended. |
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| HOW TO FIT BRAKE PADS | | | | Brakes are a critical safety system of a vehicle. The brake system should not be interfered with by anybody who does not have the appropriate skills and experience. Brake pads should replaced by a qualified mechanic. | | | | | These are general instructions, for the assistance of experienced technicians. For more detailed instructions pertaining to a specific vehicle, consult the manufacturer’s service manual. | | | | Approved safety equipment should be used at all times. Use the correct tools for each task. Before starting work, ensure these instructions have been read and understood completely. | | | Raise the vehicle off the ground and remove the wheels. If a vehicle hoist is not available, ensure the wheels are chocked and the vehicle is supported by chassis stands on level ground. Do not work under a car supported only by a jack.
Inspect the caliper for wet patches which may indicate a brake fluid leak. Clean the brake with Bendix Brake and Parts Cleaner. Do not use compressed air, dry brushing, oil-based or petroleum-based solvents.
Remove the brake pads from the caliper. The procedure varies greatly depending on the type of caliper. It may be helpful to work on one brake at a time, leaving the opposite brake assembled as a reference. Unplug any electronic pad wear indicators before starting. | | | | Sliding calipers: | Some sliding caliper designs allow the caliper body to pivot on the upper slide pin when the bolt is removed from the lower slide pin. Swing the caliper body away from the anchor bracket to provide access to the pads. Take care not to damage the flexible brake hose.
Some sliding caliper designs require the bolts to be removed from both slide pins, and the caliper body lifted away from the anchor bracket to provide access to the brake pads.
Some sliding caliper designs do not use a separate anchor bracket, with slide pins mounted to the suspension knuckle. Remove the caliper body from the suspension knuckle, or pivot the caliper body around the upper slide pin, to provide access to the pads.
Some sliding caliper designs use pins and clips to hold the caliper body to the anchor bracket. Refer to manufacturer’s instructions for disassembling these calipers if necessary.
The pads may be secured in the caliper body using clips or springs, or may be captive in the anchor bracket. Take note of the arrangement of clips when disassembling the caliper to remove the pads. Springs may be under tension, and require care to disassemble safely. | | | | Opposed-piston calipers: | Most opposed-piston caliper designs have a window in the bridge of the caliper to allow access to the pads. The pads are typically located in the caliper using pins and clips. Remove any pins or clips and withdraw the pads through the window.
Some opposed-piston caliper designs require the caliper to be removed from the suspension knuckle to provide access to the pads. | | | | Other caliper designs: | For other caliper designs, consult manufacturer’s instructions.
Remove the caliper from the suspension knuckle (if it was not completely removed during step 3), taking care not to damage the flexible brake hose. Secure the caliper to the vehicle, in a convenient position that does not put undue stress on the brake hose.
Inspect the condition of the used pads. If the pads show uneven wear, the caliper may need to be overhauled or replaced. Refer to local regulations for disposal of used brake pads.
Inspect the condition of the caliper. Ensure all dust boots, caps and seals are in good condition, and that sliding surfaces are not damaged. For sliding calipers, lubricate the slide pins and ensure they are straight, in good condition, and allow the caliper to slide freely. | | | | Check that the brake hose is in good condition. Replace any component that shows signs of damage or deterioration. | | | If the caliper uses a stepped piston design, ensure the orientation of the step is correct according to the manufacturer’s instructions.
Rotors should be machined if they are to be re-used. Use a micrometer to measure the thickness of the rotor at several radii across the face. The minimum thickness is marked on the rotor. If a rotor is under minimum thickness (or will be under minimum thickness after machining), or if it is tapered, replace the pair of rotors. | | | | If on-vehicle machining is not possible, of if the rotor is to be replaced, remove the brake rotor from the vehicle following the manufacturer’s instructions. If wheel bearings are integral to the rotor and are to be replaced, it should be done before machining. | | | | Machine the rotor using the slowest feed rate. Do not take heavy cuts. The final cut should be very light to minimise grooving of the braking surface. | | | | After machining, finish both braking surfaces of the rotor with 240 grit emery to obtain a smooth non-directional surface finish. Clean the rotor with Bendix Brake and Parts Cleaner. If the rotor was removed from the vehicle, re-fit the rotor following the manufacturer’s instructions. | | | | Use a dial gauge to measure installed rotor run-out. If the rotor is the type that is located and held in place by the wheel, use the wheel nuts to temporarily locate the rotor on the hub. | | | | Installed rotor run-out should not exceed 100µm (0.1mm). If acceptable run-out can not be achieved, further investigation is required. The rotor, hub or suspension components may be damaged. | | | Mount the anchor bracket (for sliding calipers) or the caliper body (for opposed-piston calipers) on the suspension knuckle. Tighten the bolts to the manufacturer’s recommended torque. Note: if the caliper requires pads to be fitted before caliper installation, complete steps 10-11 before mounting the caliper.
Clamp the brake hose and open the bleed screw on the caliper. Use a bleed hose to catch excess brake fluid in a suitable container as you push the pistons back into the caliper. Pistons should be pushed back by hand or using a piston retraction tool. Ensure all pistons can move without binding. Take care not to expose skin, clothing or paintwork to brake fluid. | | | | Calipers with an integral park brake often require an alternate method to retract the piston. Consult the manufacturer's instructions. | | | Fit the new brake pads to the caliper body or anchor bracket and reassemble the caliper. For sliding calipers, fasten the caliper body to the anchor bracket and tighten all bolts to the manufacturer’s recommended torque. Ensure all clips, pins etc. are correctly installed.
Complete pad change and inspection of all brakes.
Flush and replace the brake fluid, unless service records show that it has been replaced within the last 12 months. Brake fluid should be flushed and replaced at least once every two years, as it absorbs water from the atmosphere which reduces it’s performance. Refer to the vehicle manufacturer’s recommendation for the correct specification of brake fluid.
| | | | To avoid contamination of the brake fluid, clean the master cylinder reservoir with Bendix Brake and Parts Cleaner before opening. Add new brake fluid to the reservoir as required, from a fresh sealed container. Flush new brake fluid through the entire brake system, starting at the wheel furthest from the master cylinder. Collect the used brake fluid in a suitable container. Refer to local regulations for disposal of used brake fluid. | | | Bleed the brakes following the manufacturer’s recommended procedure, paying attention to the appropriate bleeding order.
Apply the brakes several times to set the brake pads and pistons in position. Top up the brake fluid reservoir if necessary. If the brake pedal does not feel firm under foot, repeat step 14. Attach and adjust the park brake according to the manufacturer’s instructions. Wipe rotors down again with Bendix Brake and Parts Cleaner.
Fit the wheels, lower the vehicle to the ground and tighten the wheel nuts to the manufacturer’s recommended torque.
Test drive the vehicle to ensure correct brake operation.
Follow the appropriate bed-in procedure for the brake pads fitted.
The brake system should be inspected by a qualified mechanic at least once per year, or more often if the vehicle travels long distances or is subject to heavy duty conditions. | |
| GUIDE TO GENERAL BRAKE PROBLEMS | | | | Problem | | Probable Cause | Corrective Action | Low/Spongy Pedal
 | Pedal nearly touches floorboard before
brakes function.
No brake reserve. | No fluid in master cylinder. | Check system for fluid leak and repair. | Excessive free play in brake pedal linkage. | Adjust for proper linkage. | Pad "knock-back". | Examine rotor run out and parallelism, bearing adjustment, etc. | Excessive clearance between linings and drums. | Adjust brakes. | Contaminated fluid. | Replace with approved brake fluid. | Residual line pressure valve faulty. | Check/replace. | Air in hydraulic system. | Bleed brake system. | | High Pedal Force
 | Excessive stopping distance, excessive
pedal effort, brakes
do not react properly | Worn/glazed pads or linings. | Replace with new pads or linings. | Frozen calipers or wheel cylinders. | Free up and replace if necessary. | Brake booster failure. | Inspect booster Assy. Repair as required. | | | |  | Brake Drag
 | Sticking brakes may
be failing to release properly. | Brakes adjusted too tight. | Readjust and allow sufficient clearance between lining and drum. | Master cylinder by-pass port blocked. | Clear blockage. | Weak pedal return spring. | Install new springs. | Distorted backing plates. | Replace with new plates. | Sticky wheel cylinder. | Repair with new cups. | | Brake Pull
 | Car pulls to one side
when brakes are
applied. | Contamination of pads or linings with brake fluid, oil, grease, etc. | Clean or replace pads or linings. | Unmatched pads or linings. | Replace with correct parts. | Faulty caliper pad alignment. | Check for loose caliper mounting bolts, guide pins, broken clips. | Unequal brake adjustment. | Readjust all brakes. | Seized Calliper. | Overhaul both calipers (ie. pin and seal kits) on that axle. | | Brake Grab
 | "Touchy" brakes that
grab with least pressure. | Contamination of pads or linings with brake fluid, oil, grease, etc. | Clean or replace pads or linings. | Caliper not aligned with disc. | Correct alignment. | Mounting bolts loose. | Tighten to specified torque. | Brake lines, hoses kinked, collapsed or clogged. | Repair or replace. | Caliper pistons or slides seized. | Free up and replace if damaged. | | Brake Noise
 | Brakes should operate
with minimal amount of noise.
However excessive
squeal, screech,
groaning, grinding
chatter or rattle means your brakes need attention. | Too much lateral run out of rotor. | Correct runout to manufacturers spec. | Worn pads or linings. | Replace with new pads or linings. | Twisted brake shoe. | Replace brake shoes. | Weak or broken spring components. | Replace with new springs. | Drums out of round. | Turn or replace drums. | Loose wheel bearing. | Adjust or replace faulty parts. | Foreign particles embedded in material. | Replace with new pads or linings. | Faulty caliper alignment. | Readjust. | | Vibration
 | Brake pedal, steering wheel or entire wheel shakes, vibrates or pulsates when brake is applied. | Rotor run out and parallelism. | Resurface disc brake rotors. | Wear in steeringand suspension components. | Examine and replace worn components. | Wheels out of balance. | Wheel balance required. | | Brake Wear
 | Premature wear can be caused by a number of faults in the brake
system.
To avoid costly repairs have the brakes checked at least once a year. | Wrong type of pad or lining material for operating conditions. | Replace with correct pad or lining material for application. | Caliper pistons and/or pins seized. | Fit pin and seal kits. | Extremely rough rotor surface. | Regrind rotors |
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