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. 

Brake servo fault finding guide

If a customer draws attention to a sudden change in the feel of the brake pedal in their car there can be many possible causes, such as air in the system, fluid leakage, or a binding brake caliper to name just a few. Another possibility – especially if the complaint is one of excessive effort needed to stop the car – is that the vacuum brake servo, also referred to as a brake booster, is defective in some way. To diagnose whether the servo system is working correctly, ZF Aftermarket engineers recommend using a handheld vacuum tester and a structured series of tests as follows.

Basic test

With the engine switched off, press the footbrake repeatedly until the pedal feels firm – this releases any residual vacuum in the system. Still pressing firmly on the brake pedal, start the engine. If the pedal gradually sinks toward the floor of the vehicle with the engine running, vacuum is being generated. This suggests that the fault probably lies elsewhere in the braking system rather than with the servo, although further checks should still be carried out to confirm that the system holds vacuum for an adequate period of time. If the pedal doesn’t move at all, insufficient vacuum is being generated and there is definitely a fault in the servo system.

General system inspection

Check the entire vacuum system including all connected components such as the exhaust gas recirculation (EGR) valve, engine vacuum pump and fuel pressure regulator. Examine hoses and connectors for splits, cracking or perishing and replace any items that are defective or no longer fit snugly.

Non-return valve functional description

The non-return valve is installed in the hose between the brake servo and the intake manifold or the vacuum pump of the vehicle’s engine. When the engine is switched off, the valve closes to maintain vacuum in the brake servo, storing brake-assisting energy until the engine is restarted. The non-return valve also prevents fuel and oil fumes from entering the brake servo and damaging its internal rubber diaphragm. When the engine is running and the brake pedal is operated, a pressure differential occurs between the inlet and outlet ports of the valve, causing it to open against spring pressure and allow vacuum to be applied to the servo (Figure 1). When equilibrium is reached and the vacuum is equal at each port of the valve, the spring closes the valve (Figure 2). In this way, vacuum in the brake servo is maintained at a constant level.

Fig. 1:  Brake servo non-return valve in open position

Fig. 2:  Brake servo non-return valve in closed position

Failure of the non-return valve has several possible consequences:

Any of these defects will reduce or eliminate braking assistance for the driver, potentially increasing stopping distances and heightening the risk of an accident.

Non-return valve tests

Connect the handheld vacuum tester to the engine side of the non-return valve, either by disconnecting any small vacuum pipe present or by teeing into the main vacuum pipe from the engine or the vehicle’s vacuum pump (Figure 3). Start the engine and leave it running until a steady vacuum registers on the gauge. Switch off the engine and check that the vacuum is maintained for a period of five minutes (Figure 4).

Fig. 3:  Testing engine side of the non-return valve

Fig. 4:  Vacuum must be maintained for five minutes

Prise out the non-return valve from the servo unit and connect the vacuum tester to the servo side of the valve (Figure 5). As before, start the engine and leave it running until a steady vacuum registers on the gauge. Switch off the engine and check that the vacuum is maintained for five minutes.

If either non-return valve test fails, check the non-return valve for oil contamination or damage and replace it as necessary.

Fig. 5:  Testing servo side of the non-return valve

Servo vacuum leakage test

With the non-return valve removed from the servo unit, connect the vacuum tester to the servo (Figure 6) and operate the tester’s hand pump to generate a reasonable level of vacuum. Once again, this vacuum must be maintained for five minutes.

Fig. 6:  Testing the brake servo

If this test fails, check the servo unit for contamination or damage such as corrosion at the seam(s) between the parts of the housing or a perished grommet where the non-return valve is fitted to the servo. Be aware that any damage may be internal due to the ingress of oil/fuel fumes and therefore not externally visible. Depending on the nature of any problems found, it may be necessary to replace the grommet or the complete servo unit. Where new parts are required, ZF recommends the use of Original Equipment components such as those provided within its extensive portfolio comprising the renowned Lemförder, Sachs, TRW and Boge brands.

Step by Step: Electric Park Brake release

First to market with its TRW branded Electric Park Brake (EPB) system in 2001 – which pioneered with Lancia, Audi and VW – the ZF business has now produced in excess of sixty million EPB motor-on-caliper units.

This article looks at what to do in the event of the brake failing to release, demonstrated in this video.

The cause for this defect is an interrupted power supply to the electric motors (actuators) which then can no longer release the brake. The exact fault can only be identified by experienced professional mechanics using the appropriate diagnostic tools.

Emergency Release

To get the vehicle to the garage, however, it may be necessary to open the brake with the emergency release. Some vehicle manufacturers offer integrated systems for this. The exact handling is described in the operating instructions for the vehicle. For vehicles where this is not the case, this piece describes a general option for emergency release.

One important note: Do not attempt to release the brake by connecting an external power source. This can destroy the actuator due to different electric controls for the system variants!
To release the brake, you should therefore proceed as follows:

EPB

  1. Remove the connector
    Disengage the connector with a suitable tool and pull the connector from the actuator.

Note: Some EPB systems use actuators with an integrated cable. In this case, the plug connection must be disconnected on the cable harness of the vehicle. This is generally located in the corresponding wheel housing!

 

 

 

Gehaeuse mit Motor
2. Remove the fixing screws of the actuator
Release and remove both fixing screws of the actuator and any cable holders.

 

 

 

 

TRW EPB3. Remove the actuator
The actuator can now be pulled from the housing in the direction of the arrow.

 

 

 

 


TRW EPB4. Open the brake
Use a suitable tool to turn the spindle in the direction of the arrow (clockwise) until the brake is free.

 

 

 

 

 

TRW EPB5. Mount the actuator
Insert the actuator, ensuring correct seating of the sealing ring.
Note: The motor may have to be rotated slightly during installation so actuator and spindle engage.
Insert the fixing screws
Attention: Ensure to insert and tighten the screws by a few turns by hand. If the thread is damaged, the complete brake caliper has to be replaced!



Tighten the screws with the torque specified by the vehicle manufacturer. Install the connector.

A library of technical tips, ‘How To’ guides, videos and fitting instructions can be found at TRW’s Tech Corner. To register, simply go to: www.trwaftermarket.com/en/Tech-Corner

Advice to promote successful suspension repairs

Multi-link suspensions have largely replaced conventional wishbone suspensions, increasing driving dynamics and comfort. The modern design, explains TRW, features one or both wishbones broken down into multiple components, so that significantly more moving parts are installed.

The distance between wheel centre and steering axle – the so-called disturbing force lever arm – is relatively short. This allows disturbing forces (propulsive, braking and lateral guiding forces) to be kept away from the steering as much as possible. However, the joints move closer to the brake, which automatically exposes them to higher temperatures, resulting in significantly higher demands on the installed rubber sleeves and plastic bearing shells, as well as for the grease used.

More moving parts also means more joints connecting the parts, this results in a higher sum of ‘moments’, which are divided into breakaway torque and running torque. Breakaway torque results from the force required for setting the ball pin into motion from its resting position. The running moment results from the force required for rotating the ball pin or moving it back and forth in the joint.

Development engineers try to keep these moments as small as possible as this ensures, for example, that after cornering the front axle returns to the centre position independently and smoothly and that the suspension responds more sensitively. Today, so-called low-friction ball joints are used that have a substantially lower friction moment than previous types.

While a smoothly moving ball pin used to indicate increased wear of the ball joint, this is no longer the case. Modern ball joints have distinctly lower breakaway torques and running torques.

DEVELOPMENT AND DESIGN OF A MULTI-LINK SUSPENSION

The product specifications defined for a multi-link suspension are determined during extensive test procedures on a test bench as well as in the vehicle. The associated moments (running torque and breakaway torque) as well as the damping properties of a joint always have to be considered within the overall system.

The influencing factors for steering systems, suspension, springs, brakes and tyres are extremely important for the functioning of the overall vehicle and for vehicle safety. Altering individual components and specifications is only permitted with consideration of the overall concept and always requires approval from the vehicle manufacturer.

Screen Shot 2017-11-29 at 18.41.28MAINTENANCE AND REPAIR

Mechanics should observe several points when replacing individual components.

When replacing a ball joint, the eye and the rubber contact surface in which the joint is installed have to be cleaned and any rust removed. The contact surface must be free from rust or the rubber sleeve will rub against the rough surface and leak. Dirt and moisture can enter the joint, which leads to premature joint failure.

During installation, it has to be ensured that the corrosion protection layer of the circlips is not damaged, as rust causes them to lose their spring force, allowing moisture ingress into the joint, significantly affecting service life.

Never tighten the ball joint with an impact wrench. There is a risk the ball pin could start to rotate so fast that the plastic bearing shell becomes deformed by the frictional heat, leading to play in the system. Furthermore, the tightening torque can be exceeded, causing the ball pin to move too high into the eye of the stub axle. This means the rubber sleeve can no longer fulfil its sealing function, allowing dirt and moisture to enter into the ball joint.

The rubber bearing on a control arm may only be tightened when compressed and without load to avoid twisting and therefore applying pre-tension to the bearing.

The installation errors described here can lead to premature wear or even failure of the replaced part. Garages should always carry out a wheel alignment after replacing suspension parts, even if only axle components were released. If these simple rules are followed, all suspension repair work can be carried out successfully.