Category Archives: Apec

Bedding-In Brakes

Bedding-In Brakes

The “bedding-in” for brakes is essential for the brakes to perform optimally and friction is key for efficient braking. Here, Apec explains Bedding-in as well as the Material Transfer Process.

Definition

Friction is a force resistant to movement between contacting areas. In braking there are 2 types of friction processes that occur during the material transfer process. To understand the bedding in process and material transfer process, we need to comprehend the difference between the 2 types of friction processes, which are the abrasive and adherent friction process.

Abrasive Friction Process

When the brake pads are compressed against the brake disc, the pressure and contact from the 2 surfaces will generate heat and cause the breaking down of particles on the surface of the material. If you could mount a microscope on a brake pad, you would see tiny particles of the pad and disc breaking away from the surfaces as they contact each other. As this is happening, the heat is physically and chemically changing the exposed friction material as particles are being torn or sheared from both components. This leads to the mechanical wear of the discs and pads, consequently having to be replaced when worn past their limit of performing efficiently. Some particles become part of the friction surface of the disc, while others are cast off and form brake dust, that stick to wheels and eventually will be washed down the drain, potentially polluting the environment.

Adherent Friction (Bedding-in) Process

The particles that become part of the friction surface results in the adherent friction process, which is also known as the bedding in process. This process transfers a layer of brake pad material onto the disc. Once the brake pad material is sufficiently transferred to the surface of the disc, it increases the coefficient of friction or, simply put, makes the brakes more “grabby” to each other. Because there are two forces at work here, adherent friction and pressure, stopping distances can be improved by up to 20%.

The material transferred acts as a sort of adhesive, that literally sticks to the brake pad as it’s being compressed against the disc. This creates a barrier between the pads and the disc preventing the disc from being ground down to a powder by the brake pads and vice versa meaning your brakes will last significantly longer. Adherent friction is not as a destructive force as abrasive friction due to that protective barrier preventing the brakes from being worn down as fast. To ensure continuous smooth operation of brakes, the process of material transfer from the brake pad must be evenly distributed on the disc surface.

Adherent friction is a totally evolving process, as heavy braking will remove some of this material transferred to the disc and will need to be replaced under normal braking conditions.

Recommended Bedding-in Procedure

Bedding-in new discs and pads should be done with care to ensure even material transfer. Correct bedding guarantees that new brake pads and new discs work flawlessly together. During the test drive, the vehicle should be driven at a moderate speed (30-35mph) and brakes should be applied gradually (normally) without coming to a complete stop, to initiate the material transfer process. This process should be repeated for 8-10 times. Avoid more than a minute between each brake application to maintain the temperatures needed for the bed in process. When handing the vehicle back to the customer, it is essential to advise them to brake gradually (normally) and to avoid feathering their brakes or heavy braking for about 200 miles to continue the bedding in process correctly.

Potential Issues

Too little heat during bedding keeps the pad material from transferring to the disc face. Therefore avoid feathering the brake pedal or over-heating the system with heavy braking. This can generate uneven pad deposits due to the material breaking down and sticking to the disc, causing a Stick/Slip situation. Once this has happened, heavy braking will lead to uneven heat build-up due to the uneven distribution of friction material across the disc, with high-spots heating excessively in comparison to the rest of the disc. In the event of this happening this will lead to the disc suffering from excessive Disc Thickness Variation.

Material transfer is a continuous process after bedding in and anything affecting the even transfer of material on the brake disc will cause issues. The biggest cause of uneven material transfer is excessive lateral runout. Please see our article on understanding brake judder for a detailed explanation. Other causes may be as simple as poor technique, using the brake pedal to slow the car rather than engine braking on serious inclines or repeated ‘emergency’ style stops without adequate cooling time or even a mechanical issue such as a sticking pad, slider or caliper that affects the even material transfer process.

Apec focus on quality

All Apec brake pads and manufactured from the latest generation friction materials and benefit from a unique “High Pressure Treatment” (HPT) scorching process to provide superior initial performance and easier bedding in. Apec partially coated discs are made to match OE standards. Just like original discs that have coated hubs and edges, Apec discs have them too! However, there is no coating on friction surface to facilitate the even material transfer process. Without any coating on the friction surface there is nothing to contaminate the pads to reduce their efficiency.

Get Your Head Over Squeals

Get Your Head Over Squeals

In this guide, our friends over at Apec Brakes teach us all about squeals – what causes them, and how to stop them.

Every motorist is likely to have experienced a noise coming from their braking system at one point or another. The very nature of a vehicle’s brakes means a massive amount of pressure and friction is exerted over two surfaces in order for the process to be executed effectively. This means that the likelihood of external factors affecting a certain part of the system is relatively high compared with other aspects of the vehicle’s dynamics.

What causes brake squeal?

The three most common causes of brake squeal:

1. Brake pads are running low

If brake pads do not have an electronic wear indicator, Apec’s replacement brake pads are fitted with a pre-installed physical wear indicator – a small tab of hardened steel which begins near the end of the pad’s useable lifespan and is designed to make an audible, relatively loud noise when it eventually comes into contact with the disc. Customers should be made aware that driving around when the tab has reached this point for too long has the potential to cause irreversible damage to the disc.

2. Change in pad material

Squealing can also occur when budget replacement brake pads are purchased. Since the removal of asbestos-based pads from everyday circulation, these more affordable items will often contain a higher metal content than quality brake pads such as Apec’s (which contain a higher organic content in their make-up). These small pieces of metal in the pad’s material have several detrimental effects aside from creating large amounts of noise, including decreased braking performance, damage to the discs and increased amounts of brake dust causing discolouring to alloy wheels.

3. Excessive play or damage in braking system components

Play or damage to part of the braking system is relatively common and is often signified by reduced effectiveness and/or a squealing noise. The majority of modern cars rely upon a ‘floating’ brake caliper system, utilising caliper sliding pins to allow the unit to slide evenly towards the disc when the brakes are applied, offering even wear through the pad.

Damage to the slider pins is common and a relatively easy fix when the correct equipment and parts are used. There’s also the potential for a spring or abutment paint shim to lose its shape and strength over time, causing excessive play to occur between the pad and caliper, again leading to uneven wear and squeal.

How can brake squeal be fixed or prevented?

Apec offers solutions to the majority of common causes of brake squeal in the form of various kits and parts. Here are the most common solutions to fixing brake squeal:

Replacing the caliper sliders

Rust or damage to the caliper and its slider pin is one of the most common causes of ineffective pad wear and brake squeal. Due to the large amount of movement involved, it’s likely that foreign material or moisture will make its way through the slider seals over time, affecting the performance of the sliding mechanism.

Heavily corroded caliper and piston

It is imperative that sliders are always lubricated with a non-petroleum-based grease. Owners should be made aware that, when washing their wheels, a pressure washer can remove this grease if powerful enough.

Replacing the brake fitting kit

Another ‘weak link’ in any brake system is the pad abutment point shim and (or) the retaining spring. For disc brakes, this comes in the form of bent metal housings used to hold the caliper in a strict, tight position in relation to the disc at all times, complete with springs to further maintain the correct positioning. In drum brakes, fitting kits consist of two springs which perform a similar role of holding the brake shoes in the correct position in relation to the drum itself.

Apec tests have shown that these kits can lose up to 50% of their effectiveness in just two years of use, meaning it’s a thoroughly important and often overlooked servicing part. A loss in effectiveness equates to increased play in the parts of the brake that apply pressure when the vehicle is required to slow down, which can also commonly cause squeal.

Correct fitting of Apec pads

Perhaps the most simple but still a very common cause of brake squeal is simply the incorrect fitment of new brake pads, many of which are now directional or require a retaining spring. As one would imagine, fitting a directional brake pad the wrong way round can lead to brake squeal, while the removal of a retaining spring will eventually lead to vibration and oscillation. With modern braking technologies increasing the complexity of braking systems, it’s more important than ever for owners to head to an established workshop, even for work such as replacing brake pads to be carried out.


ABS Sensors

An anti-lock braking system (ABS) is a vehicle safety system that allows the wheels of a car to maintain tractive contact with the road surface while braking, preventing the wheels from locking up (ceasing rotation) and avoiding uncontrolled skidding. It is an automated system that uses the principles of cadence braking. Cadence braking is a skill practiced by skilful or professional drivers in vehicles without or prior to ABS technology. The ABS system does this at a much faster rate and with better control than many drivers could manage. ABS generally offers improved vehicle control and decreases stopping distances on dry and slippery surfaces. However, on loose gravel, ice or snow covered surfaces, ABS can increase braking distance, although still improving vehicle steering control.

Since their introduction, anti-lock braking systems have been improved considerably in a bid to further improve driver safety and comfort. Later technology not only prevents wheel lock up under braking, but can also provide data for the on board navigation system, traction control system, emergency brake assist, hill start assist, electronic stability control and the front-to-rear brake bias. None of the above would be possible without wheel speed sensors.

The ABS, or wheel speed sensor in a relatively simple yet vitally important part of the ABS system as it is used to communicate the rotational speed of the wheel to the ABS control module.

Wheel speed sensors are installed directly above or next to the pulse wheel, these are also known as a tone wheel, but more often than not, called the ABS ring. The ring is attached to a part of the vehicle that is rotating at the same speed as the road wheel, such as the wheel hub, brake disc, CV joint or the drive shaft.

Types of ABS Sensors

ABS sensors are classified in to two different types, Passive and Active. Passive is without a power supply and Active is with a power supply.

Passive sensors

These comprise of a wire coil wound around a magnetic core and a permanent magnet. The pole pin inside the coil is connected to the magnet and the magnetic field extends to the ABS ring. The rotational movement of the ABS ring and the associated alternation of teeth and gaps effects a change in the magnetic flux through the pulse wheel and the coil. The changing magnetic field induces an alternating voltage in the coil that can be measured. The frequencies and amplitudes of the alternating voltage are related to the wheel speed. The sensor creates a AC signal that changes frequency as the wheel changes speed. The ABS control unit converts the AC signal to a digital signal for interpretation.

Structure of a passive sensor
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Output wave of a Passive sensor

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Passive sensors are larger and less accurate than active sensors and only start to operate when the wheel reaches a certain speed, therefore they have limited operation at lower speed. They are also unable to operate in reverse, so thus unable to determine the direction of travel.

Active sensors on the other hand are a lot more accurate and are able to detect speeds of less them 0.06 mph, this is vital for modern traction control systems. Some active sensors can even detect the rotation direction of the wheels. Active sensors require an external power source to operate and work in conjunction with a toothed or magnetic ABS ring. Active sensors create a digital signal which is transmitted to the control unit in the form of a current signal using pulse width modulation.

Structure of an Active sensor

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There are two types of active sensor. The Hall sensor and the Magneto-resistive sensor

Hall sensor – The hall sensor uses the Hall effect, which is a generation of a voltage (the Hall voltage) across an electrical conductor, transverse to an electric current in the conductor and a magnetic field perpendicular to the current. They react to changes in magnetic fields with a voltage difference which is send to the ABS control unit as a square wave signal. They use a semiconductor sensor coupled to an electronic circuit, protecting the sensor from possible voltage spikes, and a permanent magnet.

Output wave of an active sensor

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Hall sensors record the wheel speed via either a toothed or magnetic encoder (ABS ring) often found on the wheel hub, disc or bearing. The sensors are very accurate, but must be installed with precision.

Hall sensor with a toothed ring

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Hall sensor with a magnetic ring

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The advantage of using a magnetic ring over a toothed ring is that the sensor can be a lot smaller as there is no permanent magnet required in the sensor. It is instead located in the virtually flat ‘ABS ring.’ That magnetic ring can be located in the wheel bearing, allowing them to be used in confined spaces. The variation in the magnetic field is now created by the sections of polarity within the ring.

Magneto-resistive sensor – These sensors use a magnetic encoder ring similar in appearance to the encoder ring associated with the hall sensor. However, the encoder ring associated with this sensor has magnetic arc segments which cause a clear change in resistance when passing the sensor. It is this that enables the control unit to determine the wheel’s rotational direction. Magneto-resistive sensors are much more precise, but generally more expensive than Hall sensors and require a less precise installation position, therefore meaning that it can be located further away from the ‘ABS ring’ than the other types of sensors.

Both active sensors are less sensitive to electromagnetic interference, vibration and temperature fluctuations than a passive sensor.

Failure Diagnosis

Generally speaking, ABS sensors are very reliable, however due to their location they have a tough life.
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If any of the warning lights above are illuminated, there is brake pedal judder while braking at low speeds or the wheels lock up while braking, then there is probably a fault somewhere within the ABS system.

Possible causes,

  • Corroded, cracked or swollen ABS ring
  • ABS ring blocked, damaged, missing teeth or windows
  • ABS sensor out of position.
  • Damaged ABS sensor from impact with road debris.

One of the most common calls that we currently receive into our technical department is for the Peugeot 308 rear. This particular brake disc also contains the bearing and ABS ring. The workshop replaces the disc, only to find that the ABS sensor is now in contact with the ABS ring of the new disc. Apec or the motor factor usually get the blame for an incorrect part, however Apec parts are made to the exact dimensions as the original disc so it is not the disc that is at fault. What actually happens is that over time, corrosion forms and builds up under the mounting point of the ABS sensor. This forces the sensor towards the ABS ring and begins to wear the surface of the ABS ring. If this is noticed before the disc is bolted up, then usually the sensor (if not too worn itself) can be unbolted and the corrosion removed. However, if it is not noticed then is can result in the ABS sensor snapping as the vehicle is driven out of the workshop.

Correct Fitment of WIR5243 to PAD1448 on the rear of Jaguar XF & XJ models

 

To correctly fit the wear sensor, first remove the pad spring fitting from the top of the pad using a suitable tool.

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Insert the wear sensor into the spring.Screen Shot 2017-03-28 at 09.20.19

Insert the spring and wear sensor back it to the pad using a suitable tool.Screen Shot 2017-03-28 at 09.22.56

Pay special attention, not to apply force on top of the plastic sensor housing during this step to avoid damaging the sensor housing.

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What Causes Brake Judder?

Apec Braking take us through the preventative steps you should take to avoid brake judder.

Brake judder is one of the few ailments that can affect all types of vehicles. Brake judder manifests itself in vibration, and it is a sensation that can be felt through the steering wheel, through your pedals and potentially through your seat. Depending on the severity, a car’s chassis has even been known to pulsate.

Customers affected by brake judder often jump to one conclusion: that they’re experiencing a side effect of warped discs or, more technically, distortion. The truth about the real causes of brake judder are, however, far more complicated; in the majority of cases warped discs have nothing to do with disc manufacture or quality and everything to do with fitment or driver behaviour.

In most cases, brake judder develops or worsens over a given timeframe. This is vital to understand from a technician’s standpoint as it highlights that when fitted, a customer’s brake disc was within manufacturer tolerance, and thus aggressive braking or a fitment issue is the root cause of the problem. In fact any disc, regardless of quality or materials, can warp (distort) under the correct circumstances.

Main causes

Let’s begin with the main cause of brake judder: Disc Thickness Variation (DTV). One of the major causes of DTV is lateral run-out caused by improper cleaning of the hub surface. Similar to the butterfly effect, even the most minute particles of rust caught between the disc face and hub (measuring as small as 0.04mm) can lead to lateral run-out (where the turning disc starts to deviate from its axis) in excess of 0.1mm when measured at the centre of the braking surface.

The important point to note is that while this deviation may not immediately induce brake judder, it has provided the foundations for a vibration that will eventually lead to it, causing potentially irreparable damage to the braking disc (although this may not occur for over 2,000 – 5,000 driven miles).

Secondly, it is essential brake discs and pads are “bedded in” properly, and customers need to be aware of the potential damage caused by excessive heat build-up. During the first 100 miles the driver should drive normally but try to avoid excessive braking which would elevate the temperature of the disc and pad.

All Apec brake pads go through a ‘High Pressure Treatment’ process, burning off many of the resins and gases at the factory that would normally find their way into the atmosphere during bedding-in; this gives a good initial braking performance.

During the bedding process a layer of friction material is evenly distributed across the brake discs. Too little heat during bedding keeps the material from transferring to the rotor face. Feathering the brake pedal while overheating the system can therefore generate uneven pad deposits due to the material breaking down and sticking to the disc, causing a stick/slip situation.

Once this has happened, heavy braking will lead to imbalanced heat build-up due to the uneven distribution of friction material across the disc, with high-spots heating excessively in comparison to the rest of the disc. If the temperature at these high-spots exceeds 650 ̊C cast iron changes structurally, transforming into an immensely rigid substance called ‘Cementite’.

As the disc is now composed of varying materials of different strengths, judder will progressively get worse, which explains why customers often return with their vehicles months after installation. This cause may be as simple as poor technique, using the brake pedal to slow the car rather than engine braking on serious inclines and repeated emergency stops without adequate cooling time!

Other factors

Outside of DTV, judder can also be caused by uneven torque on wheel bolts and issues regarding floating, fixed and sliding calipers. Fixed calipers have pistons on both sides of the discs due to the stationary caliper housing.

Excessive run-out will cause piston movement and can result in pedal pulsation and binding pads in the caliper will cause DTV. Sliding or floating calipers that aren’t sliding or that have seized will prevent the caliper housing from moving, so check the slider bolts for movement and corrosion and replace, if necessary. Always replace springs where a floating caliper is fitted.Apec-braking-300x200

Poor quality pads may also be a root cause of brake judder as the friction material can overheat quickly, particularly if the brakes are used often and aggressively. It is also possible to warp a vehicle’s hubs, which will always result in brake judder. Again the root cause of a warped hub is excessive heat build-up caused by excessive friction.

Excessively worn or poorly fitted wheel bearings can also cause run-out at the hub. There are also occasions where manufacturer error can be the root cause of brake judder, but with modern machining and production lines this is increasingly unlikely.

How can technicians minimise brake judder?

Technicians must check disc thickness before refitting a disc, as if it’s outside manufacturer tolerances then it isn’t a serviceable item and requires replacement. Technicians are advised to pick eight equidistant points around the perimeter of the disc and to never base a determination of thickness on a single spot. Any variation in disc thickness will translate into brake judder.

You should always check lateral run-out, even when fitting new discs. With the use of a dial indicator you should target 0.05mm – 0.10mm as your maximum run out limit. If you want to check run-out of the discs independently of the hub, check the disc on a lathe and perform a dial indicator reading. In an effort to remove variables from the equation, make a run-out reading of the hub flange itself, without the disc. If the flange itself is causing the run-out problem, you’ll be able to isolate the cause.

Finally, it is imperative when refitting wheels, that bolts are checked and in serviceable condition. You should check the condition of the bolt threads as well as the integrity of the bolts. Never use fasteners that are suspect and also make sure all threaded locations are clean and free of dirt, grime or other contaminants; poor quality or unclean threads can result in incorrect torque readings. Never use an airgun to fully tighten a wheel nut or bolt as this could distort an aluminium wheel. The final tightening should be done with a torque wrench in the correct sequence.

Good practice prevails

Our final piece of advice is to always service the caliper, ensuring that the pad abutment points are lubricated, sliders (where fitted) are serviceable and working correctly and replacement springs are fitted. Although it can be time consuming, it is vital that the measures we’ve advised are taken and heeded by technicians. It is also essential that the importance of correctly bedding in new discs and pads is emphasised to the customer, because that conversation is nowhere near as expensive as replacing an unhappy customer’s discs and pads.

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Apec EPB Service Tool User Guide

Apec EPB Service Tool User Guide

 

Ford Transit Rear Drums & Judder – Apec Bulletin

We would like to bring to your notice the importance of fitting and securing Ford Transit drums correctly. Failure to follow the correct procedure can result in drums being distorted and inevitably cause judder.

  • Follow normal drum fitting procedures (cleanliness of drum to hub etc)
  • Offer wheel to studs and loosely tighten wheel nuts. Do not over tighten.
  • Now gradually tighten each nut in diagonal sequence as shown below and finally to the correct torque settings.

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Modified hand brake lever – Apec Bulletin

The hand brake lever on the above part numbers of shoe have been modified to overcome certain fitting issues.

To ensure our customers are fully aware of how the brake cable should be fitted to the new lever design, we show here via the photographs how it should be assembled.

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BLOCK EXEMPTION – Apec Bulletin

What is Block Exemption? A guide for motorists and independent repairers.
On 1st June 2010 European Union legislation, ‘Block Exemption Regulations 461/2010 came into force.

This gives motorists more freedom in their decision as to who should repair and service their vehicles – now any garage can be used without invalidating the manufacturer’s warranty (subject to certain conditions).
This was as a result of four specific ‘freedoms’ that were introduced, aimed at safeguarding free competition in the entire market for vehicle spare parts, service and repair. This means:

  • parts distributors can supply parts of the appropriate quality to dealers and authorised repairers without the vehicle manufacturer / assembler using ‘dealer / repairer contracts’ or other means to prevent them.
  • anyone with a legitimate need for technical information has a right of access to it in a usable form and at a reasonable cost.

The BER covers service and maintenance during the warranty period and prohibits vehicle manufacturers’ warranties from including conditions requiring that:

  •  all normal maintenance be provided within the vehicle manufacturer’s network.
  •  all parts used must be the manufacturer’s original spare parts.

The European Commission declared that such clauses in a warranty document would represent ‘an unjustified restriction for the consumer’.

Independent repairers CAN carry out normal maintenance and repair services during a vehicle’s warranty period without invalidating the warranty conditions provided that:

  • the service is carried out in accordance with the manufacturer’s servicing schedules and is recorded as such.
  • any parts used are of ‘appropriate quality’ and are recorded as such.

All products supplied under the APEC brand are spare parts of matching quality as defined by EEC Commission Regulation 461/2010.

All products supplied under the APEC brand comply with current legislation and have full Regulation 90 approval in accordance with European Directives 98/12/EC (BER compliant) where appropriate.

UCA 230 Core Return Criteria – Apec Bulletin

 

Piston Qty and Diameter:

2 x 32mm

OE Ref:

4400L3

 

 

 

Please be aware that the Citroen C5 Brake Caliper UCA 230 is prone to being damaged around the Pad securing pin holes.

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Of course old units with this kind of damage cannot be used and therefore these cannot be accepted back for credit against the surcharge