Brakes – past, present and future

Being ‘remove and replace’ products, disc and pad heritage tends to be underreported, which is a shame, argues Rob Marshall, who looks into why they evolved and the factors influencing future development.

Any kind of brake converts kinetic energy into another form, because energy cannot simply vanish. Regardless of whether installed to a locomotive, motorcycle, an automobile, or a soap-box racer, a friction brake converts motion to heat, prior to shedding it into the air. This relatively simple task is more complicated the faster and heavier the vehicle becomes. Cooling is a significant issue that seems not very relevant on a typical push-bike but becomes more of a challenge on a hefty and fast-moving powered vehicle. The linings should also be robust and must not disintegrate, when exposed to temperature extremes. Manufacturer design and cost considerations aside, renewable brake friction components must also possess long service lives and, more recently, their composition is being placed under greater scrutiny for environmental reasons. The increased ability of high voltage hybrids (and Battery Electric Vehicles – BEVs) to drive on electric power alone is also a driving force behind more recent developments.

EARLY DAYS…

As early motorcars were, literally, horseless carriages, we should be unsurprised that the rudimentary braking systems were carried over. In some cases, the friction block that rubbed against the wheel rim was made from wood and so it is unsurprising that the situation did not last for long. As most of these pioneers had enough trouble keeping their unwieldy contraptions moving, brakes were very much a secondary consideration, until speeds had risen sufficiently high for decent retardation to be necessary.

Ferodo was the world’s first friction manufacturer, with a deep heritage in both OEM and the aftermarket. It is now a brand of DRiV Incorporated of North America.
Disc brakes were fitted to Jaguar C-Type Le Mans cars (pictured), before finding their way into production models.

With the benefit of hindsight, it seems crazy that early developers tried to keep the friction brake away from the wheels but they had the difficulty of finding an effective way to activate them either side of moving suspension, long before brake hydraulics were invented and solid push-rods were the conventions. The transmission service brake involved fitting a large drum brake to the propeller shaft, thus saddling the running gear with handling the stopping forces. Eventually, when the brakes were relocated close to the wheels, they tended to be fitted to the rear only until the 1930s, which hardly benefitted the car’s stability if the wheels locked, especially when negotiating a corner. Thankfully, as engines became more powerful, brake development matured, as cables replaced the push-rods, prior to hydraulics taking over.

KEEPING COOL…

As mentioned earlier, physics demands that a brake’s basic effectiveness is defined by its ability to absorb and shed its heat into the atmosphere. Cooling, therefore, could be enhanced if the friction parts are more exposed to the airstream. While early racing cars possessed drum brakes, their diameters could be almost as large as those of the wheel rim (affecting handling adversely), plus they were also finned, when increased their surface area. Even so, as virtually none of the disc brake is enclosed, it posed a more logical and practical solution. Wartime accelerated developments even faster than motorsport and the first successful vehicular application of disc brakes permitted WWII bombers to reach a post-landing…

Brakes have improved in numerous small ways. While the drum brake remains popular for rear hubs, the linings are now self- adjusting. Previously, technicians used to have to manipulate the manual adjusters (as pictured) every service, after inspecting the lining depth.

…standstill within a moderate distance. With peacetime restored, the disc brake was put to good use for motorcars and has since become universal but refining it was not easy. While the North-American Crosley-Hotshot was fitted with disc brakes for a limited period during the early 1950s, corrosion and clogging resulted in the manufacturer reverting to more established drum brakes.

Naturally, with the mantra ‘Race on Sunday, Sell on Monday’ ringing in several ambitious manufacturers’ ears, motorsport also adopted disc brakes but, even then, it was not a straightforward exercise. Jaguar is famed for employing Dunlop disc brakes in a trio of C-Type racing cars for the 1953 Le Mans 24 hour race, which finished first, second and fourth respectively. Stirling Moss is alleged to have stated that disc brakes did not work perfectly the moment they were installed and it took the team considerable developmental work to make them achieve their objectives.

Perhaps the most notable legislation for aftermarket pads and linings is ECE-R90 from 1995. From 2011, ECE-R90 was expanded to include brake discs and drums on a voluntary basis, which became mandatory from November 2016. The regulation also dictates that the boxes containing the friction parts are sealed before technicians open them. Do you confirm that any sealed packaging is intact?

Despite the behind-the-scenes technical challenges, the winning Jaguar averaged over 100 mph for the first time in the history of the Le Mans race, an achievement that would have been unlikely, had it not been for intense development of its disc brakes. Buoyed by success, the following D-Type racers inherited the set-up and realised a hat-trick of wins at Le Mans during 1955, 1956 and 1957. Logically, by association with motorsport, disc brakes became popular with expensive and sporting production cars. As an example, Dunlop disc brakes found their way onto Jaguar’s Mark Two saloon, prior to being rolled-out across the range.

Unsurprisingly for a company with such an innovative heritage, Citroën’s DS of 1955 possessed front disc brakes, an arrangement that continued until the death of the GSA model in 1986. These were hardly favoured by technicians, because the front discs were mounted inboard, complicating the disc replacement procedure. Renewing the pads was also far from easy, with the calliper being bolted to the gearbox, mounted just behind the engine. The Jensen 541 Deluxe (front and rear) and Triumph’s TR3 (front only) introduced disc brakes during 1956 and, after that, discs became more popular, as they were fitted to more affordable and humdrum models. Today, even the most modest-powered small car has discs mounted to
its front hubs, where most of the braking effort is focussed. This fact also explains why many carmakers fit drum brakes to the rear, especially as drum brakes remain the most effective method of incorporating a handbrake mechanism. Yet, by…

OE supplier, Delphi Technologies, highlights its prowess with reverse-engineering the original OEM product without sacrificing quality, to enable it to be first-to-market with replacement aftermarket pads.

…their very design, disc brakes are not perfect. When used as a handbrake, the disc contracts as it cools, reducing the pressure between the pad and disc. Unlike drums, disc brakes also possess no self-servo effect, which is one reason why disc brakes dictate either higher pedal pressures, or a method of power assistance. For most cars, the vacuum servo provided the solution, powered by either inlet manifold depression, or a separate pump.

Ventilated discs also have motorsport origins, before finding a commercial use. The passages within the disc more than double the surface area from which heat energy can be dissipated. They work by cold air being sucked into the disc’s structure as it turns, prior to hot air being exhaled. Other means of increasing the disc surface area and exposure to cooling air include drilling holes into the discs and incorporating grooves.

MATERIAL RELEVANCE…

A major challenge with any friction brake material is that the friction characteristics are linked to temperature and so a technical balance must be achieved. While AT shall investigate modern friction materials in greater depth in another issue, early developers experimented with different linings but the breakthrough hailed from within a domestic shed in Derbyshire. While Herbert Frood cut his teeth on manufacturing woven cloth friction materials for horse-drawn carts, he developed a more hardwearing friction material for motorcars that incorporated asbestos and established the Ferodo company (a part anagram of his name) to mass produce it. This led to the company’s first OEM contract, providing linings for the 1922 Austin 7 and, notably, disc pads for the Triumph TR3 several years later.

As the high-temperature stability and low cost of asbestos made it a core ingredient for most friction linings, the brake friction industry had a giant set-back, when asbestos’s serious health risks to technicians especially led to a ban. Significant investments were made to replace the material with alternative fibres and inorganic materials but this led to a larger variance in lining quality between friction manufacturers. After introducing asbestos initially, it is interesting to note that Ferodo was first to market with non-asbestos brake materials and started to supply the new formulation to the OEM market from 1980. Generally, friction linings have tended to become harder since non-asbestos alternatives appeared, which increases wear on the disc.

With vehicle emissions being placed increasingly under the spotlight, legislators have also been looking beyond tailpipe emissions, including those shed from tyres and brakes. In early 2020, Emissions Analytics reported that particulate emissions from both brakes and tyres can be 1,000 worse than those emitted from the exhaust. Not only are certain brake friction ingredients carcinogenic but also friction linings are responsible for a third of the world’s copper pollution. Copper, incidentally, serves as a heat stabiliser. The element is also particularly toxic to fish, an important consideration when most lining dust is washed from the roads into drains and end- up, ultimately, in waterways.

This explains why many quality friction manufacturers have marketed copper-free friction lining formulations for some time. Currently, ELV and Reach regulations govern friction lining ingredients in Europe, as does the Brakes Law (which calls mainly for the removal of copper and other heavy metals in brake friction materials by 2025) and the NSF registration in North America. Again, many quality lining manufacturers (such as TRW and Ferodo) have replaced heavy metal components with alternatives based on mineral and ceramic fibres for some time but developments have not stopped there. Apart from alternative lining materials (such as those based on cement), brake dust capture systems are also being trialled.

THE ELECTRIC DEVELOPMENT…

The arrival of high voltage hybrids (starting with Honda and Toyota) introduced not only regenerative braking (not covered in this feature) but also changed the interaction between the brake pedal and hydraulic system. To provide an ideal balance between regenerative and friction braking, brake pedal feel can be provided artificially by either an electric motor, or a pump-driven hydraulic system. Again, we shall investigate these systems in greater depth in the future. Additionally, with no mechanical noise to mask the sound of the brake friction surfaces working against one another, manufacturers have focussed on lining acoustics, as well as developing the friction characteristics to work best at lower temperatures, especially to provide optimum stopping power in emergency stop manoeuvres. Again, we will look at modern lining formulations more closely in a future issue.

Future developments are focussed more on specialised formulations for hybrid and EV applications, as well as making the dust emissions more environmentally-friendly. Pictured is a set of pads to fit the BMW i3, from TRW’s Electric Blue range.

STOP!

Brake friction servicing remains one of the most popular workshop tasks, but technology has not stood still – Rob Marshall looks at purchasing, fitting and up-selling advice.

MAKING YOUR SELECTION 

Choice is not always the best thing. Aside from practical issues, including reliability of supply from the factor, selecting brake friction components has become almost bewildering, because the market has become saturated. Despite the many options available to garages, Borg & Beck has found that most workshops stick to just one brand. However, it reasons that the typical installer needs to understand the differences between the parts on offer (see our later advice on training) and relate them to the owner/driver, because of the differences in pedal- feel and longevity that may exist between different friction brands that possess different specifications, despite all of them being compliant with mandatory R90 standards. Research is, therefore, key. Delphi agrees and states that it uses over 130 friction ingredients to create 20 friction formulations to tailor braking performance for a particular vehicle application. This compares with some suppliers that, it claims, only offer two friction specifications. MEYLE advises that it can be a positive upsell move to offer customers a choice, instead of restricting them to a single brand, but you will need to be informed enough to advise accordingly. 

Some factors have introduced their own brands, as a means of achieving economies-of-scale and building customer loyalty but, potentially, this courts confusion even further. Euro Car Parts (ECP) told us that it arranged to distribute the Pagid brand exclusively a decade ago, after it was acquired by TMD friction in 2002. Its reasoning was to combine the company’s widespread network and rapid delivery service with Pagid’s OE heritage. The strategy appears to have worked, with ECP reporting that the brand has grown phenomenally, although it is worth adding that the Pagid range extends beyond the friction components alone. 

The final word, however, has to go to Delphi, which advises that, in order to avoid inferior quality products, choose a proven quality brand that has been engineered, manufactured and tested to OE standards. 

BEYOND THE LEGAL MINIMUM 

Introduced in 1999, the ECE R90 Regulation stipulated that aftermarket brake pads should perform within a 15% tolerance of certain OE test criteria. As of November 2016, the directive was extended to cover brake discs too. ECP highlights that, because braking is a lucrative market, everyone is looking to cash-in and increase revenue, resulting in the ‘OE Quality’ statement being used to indicate that a brand complies with R90 legislation. It warns, “Many customers have started to assume incorrectly that these brands supply components to vehicle manufacturers – that is not the case. A large percentage of the brands within the braking aftermarket do not manufacture components themselves, let alone supply vehicle manufacturers.” 

Supplied to both vehicle manufacturers and the aftermarket, Federal-Mogul states that its Ferodo brand meets OE standards at the very least. It reveals that R90 legislation is a minimum standard for braking parts – for example, certain R90-compliant friction parts tend to have a standard type of noise control, or none at all, whereas Ferodo brake pads are designed with OE specific noise control features, such as chamfers and shims. Federal-Mogul reveals also that R90 conformity tests tend to take several hours, whereas OE testing can take six months and include more comprehensive testing that R90 might not consider, such as wet weather performance, temperature sensitivity, wear levels, fade, thermal conductivity, judder, durability and noise. 

You might think, therefore, that only OE suppliers seek to surpass the basic R90 requirements for both discs and pads but this is not the case. The new generation MEYLE-PD range of brake friction components are also intended to perform at a far higher level than the basic ECE certification. Brake pad manufacturer, Comline, has introduced extra test procedures as well, such as hot sheer testing, wear analysis and noise tests, which it describes as R90-Plus. 

Yet, we are not downplaying the role that R90 has in making it harder for sub-standard braking components to enter the UK car parc. All pads and discs that you fit must be supplied in a sealed box, each of which should bear a unique part number, official approval mark and evidence that permits traceability of the production process, such as a date, batch number, or source code. The box should contain fitting instructions in the correct language and the brake discs should be marked with a minimum thickness specification. 

SAVE TIME BY ACCESSORISING 

Buying extra parts, or a complete kit that includes accessories, can reduce labour times. Borg & Beck’s brake shoe kits, for example, are preassembled and it claims that you save up to 45 minutes of labour fitting time, compared to assembling and fitting the separate parts. 

Dependent on the application, however, extra parts may be needed and it can be worth enquiring if they need to be ordered separately. Apec reports that braking hardware’s tensile strength reduced by 30-50% over a two-year period, so replacing shims, for example, is a wise idea, even though the old parts do not appear to have anything wrong with them. Meyle told us that 99% of its brake discs range is supplied with a new locating screw, because they tend to corrode to the hub and are unsuitable for reuse. Its MEYLE- PD brake pads kits include ancillary parts, in cases where the company views their replacement as desirable. While Delphi admits that its brake pads are supplied with calliper bolts, fixing screws and wear indicators, where deemed necessary by OE specifications, it supplies fitting kits separately in order to limit the number of part numbers in its range. Borg & Beck highlights that its brake fitting kits include all of the components necessary to complete the tasks, including clips, springs, pins and bolts. 

LATEST DEVELOPMENTS 

While coated brake discs have been available for some time, unpainted brake discs are still widespread for older cars, so enquire with your supplier. While there is nothing wrong with unpainted discs (provided that the protective oil film is removed with brake cleaner prior to fitting), the rusting process looks particularly unattractive, if it can be seen through wide alloy wheel spokes – offering a coated alternative may be a useful up-sell for a cherished vehicle. 

Comline told us that coated discs form most of the company’s range, which are salt-spray tested for up to 240 hours to ensure optimum corrosion resistance. This tough coating is resistant to petrol, oil, brake fluid and most wheel cleaners, as well. Borg & Beck says that its water-based zinc and aluminium flake coating on its BECKTEC Brake Discs not only increases the corrosion protection but also enhances the thermal exchange properties of the disc to optimise braking performance. A technician saves time, because coated discs can be fitted straight out of the box, with no cleaning/degreasing being necessary. 

In light of increasing awareness of particulate pollution, affecting watercourses in particular, brake pad manufacturers have strived to eliminate heavy metals (especially copper) from their friction materials. Delphi and Meyle (the latter referencing its MEYLE-PD ‘next generation’ brake pads) told AT that working on reducing pollution and dust formation, while maintaining brake performance, is one of the many ongoing behind-the-scenes challenges that the brake friction industry faces. 

The increased uptake rate of hybrids and EVs, however, has made drivers more aware of brake noise, because the natural sound of the friction materials working together is not masked by the noise of an internal combustion engine. Meyle reports that previously unnoticed sounds can be perceived as disturbing. Therefore, a complaint of excessive brake noise from an EV driver might be entirely normal but latest developments may provide an up-sell opportunity. Delphi advises that selecting a brand with NVH reducing technologies, such as its own, is increasingly important. As the typical driving style is modified to take full advantage of regenerative braking systems on hybrid cars and EVs, Delphi says that advanced corrosion on the braking system changes the wear properties of pads and discs and the aftermarket needs to be aware of the opportunities that this brings. Federal-Mogul adds that brake pads are more prone to glazing under light usage conditions, as well. 

Perhaps the most obvious example of this is ZF’s TRW brand introducing the Electric Blue brake pads for EVs, as pictured. Designed to reduce braking noise, the pads are claimed to produce 45% fewer particulates than conventional pads. The current range covers 97% of the European EV car parc. 

DEALING WITH NOISE COMPLAINTS 

Noise grievances tend to be the commonest issues that damage customer confidence in garages, motor factors and brake component manufacturers. Unless the issue stems from grinding, caused by serious neglect that must be dealt with immediately, most other noises are more annoying than detrimental. Comline’s Dr Keith Ellis, Director of Braking Product Development revealed that: 

“Squeal is caused by vibrations that result from the interaction between a brake disc, brake calliper and brake pad, which tends to be influenced directly by various internal and external factors, including the temperature of the disc, or pad, the ambient temperature in which they are operating, the speed that the vehicle is travelling at and the pressure being exerted under braking.” 

Installing shims to the brake pad back-plate reduces this vibration and, therefore, controls unwanted brake noise. Comline states that there are multiple different shim derivatives available across the aftermarket, with differing levels of quality and performance, which vary between bonded gasket paper and complex laminations, using layers of different materials. For example, while Borg & Beck’s BECKTEC Brake Pads are not only grooved and chamfered to reduce noise, they also possess double rubber shims for anti-rattle and noise suppression qualities. Comline reports that its multi-layer Rubber-Metal- Rubber (RMR) shim construction is particularly effective at controlling unwanted vibrations, when combined with the pads’ noise-abating friction material and pad design. RMR is a standard feature on all new to range Comline brake pads and available on over 500 of the most popular references. 

Therefore, the brake pad’s shape can influence brake noise, too, and is one reason why directional brake pads are becoming more popular. By varying the angle at which the friction material contacts the disc, both noise and vibration can be reduced. Correct installation is crucial. Directional pads being fitted the wrong way round is one of the most common installation errors that Federal-Mogul/Ferodo encounters, for example. This has prompted the company to upload a fitting video (http://bit.ly/2WvtsUC) to its website. Delphi adds that its directional pads use either a letter, indicating which side of the vehicle the pad should be fitted, or an arrow that indicates the rotational direction of the disc and, therefore, the direction in which the pad should be fitted. Consult the fitting instructions, should you identify the pads as being directional, by the presence of a chamfered friction surface, or a crescent cut out of the shim, where no arrow is provided. Incorrectly- installed pads, or not following the correct lubrication advice in the fitting instructions, can cause excessive noise, as might wear in either the disc, or calliper. An interesting method of curing squeal is provided by BG Products. Its Stop Squeal is applied to the pads’ friction material, which reduces the likelihood of the pad and disc sticking and reduces vibration.
It is claimed that braking performance is unaffected by the application. Judder, felt by a pulsing brake pedal under light braking, as well as vibration being detected and even heard, can result not only from a damaged disc but also by incorrect fitting. Apec highlights that not cleaning the hub sufficiently, and garages not performing a run-out check, are two of the most common fitting errors that it encounters. Fitting good quality parts and providing the customer with point-of-sale advice about driving techniques for bedding-in brakes will also help reduce the chance of a dissatisfied customer returning for warranty work. 

Federal-Mogul warns about misdiagnosing the brake pad as the source, when noise could emanate from many other parts, from the wheel bearing to the ball joint. This is more of an issue on newer vehicles, where increased non-braking components are produced from aluminium, which tends to resonate more than steel. 

FITTING A MATCHED PAIR 

Federal Mogul advises that it encounters many garages installing new pads but not replacing worn discs. This tends to result in mushy brake pedal feel, increases the risk of noise and hot spots developing on the pad. Yet, when installing new pads and discs together, avoid mix-and-matching parts, because the friction surfaces are designed to work best together for optimum performance, longevity and anti-noise/vibration characteristics. Delphi Technologies, for example, offers an extended warranty only when its pads and discs are installed together. 

TRAINING FOR YOU AND YOUR CUSTOMERS 

For information on APEC’s IMI approved Light Vehicle Manual & Hydraulic Braking Systems, contact its Techmate Team on 01174 288090. Federal Mogul, meanwhile, offers Garage Gurus, a dedicated resource that provides training and technical support. Its ‘Gurus Online’ provides a 24/7 online training portal that encompasses over 30 courses, all of which are completely free of charge. ‘Gurus On-Call’, sees technical specialists provide fast answers for product and diagnostic questions either via telephone or Skype. You can also check-out over 40 on-line tutorial videos on the Garage Guru’s YouTube channel. 

For 2019, Delphi continues to develop its range for newer models especially, to provide garages with an opportunity to repair newer vehicles sooner. It highlights that new components will be supported by its usual comprehensive training and technical support. Comline has extended its range of coated brake discs to cover the Ford Fiesta (2017-onwards), Jaguar F-Pace, XE and post 2015 XF models, the Honda HR-V (from 2015), the current production Hyundai Tucson and the Kia Sportage. 

Meanwhile, Borg & Beck is emphasising its new point-of-sale materials, pictured. Aside from its ‘Brake Disc Installation Best Practice’ poster for the workshop for easy reference, it has added a rear-view mirror hanger in its brake disc boxes to help educate the driver to observe the critical bedding-in processes, such as avoiding heavy braking during the first 400 miles. It also advises that technicians pass on hints about poor driving practice, such as sitting stationary, often after heavy brake applications, with the footbrake applied firmly, which creates hot spots and increases the risk of judder developing. This can be an issue particularly with both automatic transmission vehicles and those featuring ‘Stop:Start’ technology. 

Ferodo Racing: ‘braking’ records

We spoke to Ferodo Racing to learn of cross-overs between the world of motorsport and the ultra-competitive aftermarket for brake components.

Engines racing, hearts pounding and knuckles clenched white. The smell of hot oil, clutch and brake pads fills the nostrils as drivers battle for the perfect line. The M25 is a fearsome place. As unlikely as it may sound for anybody accustomed to the cut-and-thrust nature of rush-hour London, there’s a proving ground that provides even more arduous conditions for the development of OE components: motorsport. In one vital area – braking – it is a world that has, in various forms and across a myriad of championships, been dominated by Ferodo since the company provided stopping power for the Parry-Thomas world land speed record of 1926. We spoke to Ferodo Racing to find out how much cross-over exists between brake friction technologies destined for road or race.

“In a way, motorsport is more straightforward,” explained Edward Little, technical manager, Ferodo Racing, Federal-Mogul Motorparts EMEA. “Teams are looking to stop as quickly and repeatedly as possible, with consumables lasting – as a worst- case scenario – for as long as the most demanding stage, race or conditions require. Vehicle manufacturers on the other hand, must consider the expectation for longer life-cycles of up to 60,000 km, ever more stringent NVH (noise, vibration and harshness) levels and efficiency – including the environmental impact of friction materials. If you were to fit true race-derived pads and discs to a mass-produced car, there would be a global outcry as their characteristics are simply not suitable for road use.”

“Very high-performance road pads can be used for light racing but use of race pads on the road would quickly wear OE-specification discs, not to mention be too noisy and offer compromised performance at low temperatures. Race pads are designed to withstand extremes, with an optimal operating temperature above what you would normally expect to attain in road conditions,” said Little. “Development of road and race friction materials is similar, relying on processes that determine the optimal blend of ferrous metals, carbons and ceramics, and abrasives such as silicon carbide and alumina. The search for new options is continuous. For race applications, dynamometer testing and simulation of race conditions follows – from hot to cold, or fast and slow, for example. If a product is achieving encouraging results then it is progressed to more rigorous trials and, ultimately, the greatest test: trials with race teams.”

Little explains that while the cross-over between road and race is less than you may expect, there are distinct similarities and synergistic benefits to be felt. For example, the ability to carry out high performance testing for the most extreme track- biased road car compounds, or accelerated development of components for niche manufacturers of high performance vehicles. In the past, the demanding nature of race pads has led to easy detachment from the metal backing plate. The development of mechanical methods to replace the adhesives are now benefitting road cars; a significantly reduced chance of detachment has led to far safer pads in all road conditions.

The bedding-in process is equally important for both applications and is an area that Ferodo Racing thinks could evolve in future. “Pads ‘remember’ the way they have been thermally processed for motorsport use – the performance of the microstructure is determined by it,” concluded Little. “If pads were taken straight out onto the track then performance would be inadequate, and this is the task carried out by ‘bedding-in’ new pads for road use. Although it’s currently a costly consideration, in the future we could see a scenario where aftermarket pads have undergone a similar thermal processing to provide a true ‘ready to go’ option.”

Quick to evolve and fast to stop, the world of brake friction material development is a complex one. If one thing is clear, it’s that the diversity of Ferodo’s capability and expertise is ready for track or commuter hack.