This writer was recently invited to consult on a case that involved a no-start condition on a Toyota Lexus, but as it turned out, the Lexus issue was referred to a dealership, and the consultation turned into an investigation into why the brakes on a modified, but pristine 1973 Ford Mustang Mach 1 did not work as expected. As it also turned out, the fix was an easy one, but this episode also reminded this writer of the many mistakes and oversights he had seen mechanics make over the past couple of decades when they serviced or repaired brake systems.
Note though that this writer is not suggesting that he had not made mistakes or committed oversights himself during his long career. However, despite brake systems arguably being the most important life-and-limb system on any vehicle, we all tend to become complacent when we do (or have done) something a thousand times, especially when our oversights don't necessarily result in system failures, or worse, accidents. Thus, in this article, we will discuss the most common mistakes we all make when servicing brake systems, but before we get to specifics, let us state-
We can skip over much of the detail of how this writer and the Mustang crossed paths, so suffice to say that the Mustang arrived (at the workshop where this writer was consulting on the Lexus) on the back of a recovery truck. The owner of the vehicle arrived soon after and since it turned out that, the owner was a regular customer of the workshop, this writer did not involve himself in the initial discussion of the problem.
Nonetheless, the owner of the workshop, who was a long-time acquaintance of this writer, was an expert electronic technician, and insisted on involving this writer in the matter because as he put it at the time, “… he did not know much about ancient technology”.
So, with introductions disposed of, the owner of the Mustang launched his account of the problem with the car's brakes. He started by explaining why he thought it would be a good idea to swap the vehicle's original 351 cubic-inch Windsor V8 with a highly modified 5.7 L LS1 engine mated to a T56 Tremec six-speed manual taken from a wrecked VX SS Commodore VX SS. Since LS1 engines were never an option on original Ford Mustangs, the engine and gearbox swap also required the installation of a Holley digital instrument cluster to provide accurate readings on speeds and temperatures.
This story involved a great many more details, trials, setbacks, difficulties and tribulations, none of which are relevant here, except to say that the conversion was performed by professionals, and was extremely neat and tidy. One would have sworn that the Mustang had left the Ford factory with this engine, gearbox, exhaust system and digital instruments, but from this writers' perspective, none of these modifications should have caused the brakes not to work.
As a practical matter, the Mustang’s original power brake system was typical of its time. A simple master cylinder applied pressure to the callipers on the front wheels and drums on the rear wheels and provided the brake system was fully functional, a moderate amount of pressure on the pedal should stop the car within a reasonable distance.
The Mustang’s owner agreed with this, saying that the original brakes worked well enough, but explained that since the LS1 engine and 6-speed gearbox made his car significantly faster than a standard model, he wanted to upgrade the brake system, as well. To this end, he had sourced a slightly used kit to convert the rear drum brakes to rotors, as well as (barely used) upgraded front rotors and callipers online.
By this time the Mustang's owner had spent a small fortune on the car, so to save some money, he not installed the brake upgrades himself; he also invested in a set of hugely expensive high-performance brake pads to complete the installation. It was also at this point that his brake problems started.
Despite following the bedding-in instructions that came with the brake pads to the letter, the Mustang’s brakes hardly worked. Even though the pedal was rock solid, the only way to get the car to slow down was to “stand” on the brakes, which inevitably led to the brakes fading to the point where there was no braking force at all. The Mustang’s owner invited this writer to test the brakes for himself in the parking lot outside the workshop, which test nearly ended in a crash when the Mustang just barely stopped in time to avoid a car entering the parking lot.
It was clear that this Mustang had a serious brake system problem, which prompted the owner of the workshop to make a vacant service bay available to this writer to take a closer look at the issue. Here is-
On non-ABS brake systems, the kind of problem this Mustang was experiencing has only two possible causes- provided the master cylinder is not seized or jammed. The first possible cause is a lack of vacuum assistance, and the possible cause involves tribological issues that lead to a poor conversion of kinetic energy to heat, which is the actual mechanism that makes brakes work.
To rule out a lack of vacuum assistance, this writer pulled the vacuum hose from the brake booster while the engine was running at idle. This caused the engine to start running roughly immediately, proving that a) the hose was not kinked or blocked, and b) that the brake booster diaphragm was intact since the engine resumed its smooth idling when the hose was reconnected.
Just to be sure, though, the writer disconnected the vacuum hose again and checked the operation of the restrictor that was embedded in the hose with a smoke machine. The restrictor worked fine because it allowed some smoke to pass through it in only one direction, which was towards the engine.
The next step was to remove all four wheels to inspect the rotors for signs of damage and/or overheating. This inspection revealed two things; the first was that instead of having an even silvery metallic sheen, all four rotors had a distinctly blue-ish tinge, which was proof that all four rotors had suffered potentially fatal overheating. The second thing the inspection revealed was that the brake pads on the front wheels had started to crumble around their outer edges, which was proof that the pads had suffered fatal overheating.
Of course, there are many reasons why brakes overheat, with the most common reason being simple abuse of the brakes, but in this case, the Mustang's owner had never had the opportunity to abuse the brakes. Nonetheless, the upgraded brakes had never worked even halfway decently from the first day they were installed, which meant one of two things-
The first was that the “new” rotors were already glazed when they were installed, or, more likely, the hugely expensive high-performance brake pads were not suitable for use in this application, which some quick research showed was indeed the case. It turned out that the pads were of a highly specialized purely metallic formation that only works in racing applications where brake temperatures typically range between 600 degrees Celsius and about 750 degrees Celsius, and then only in combination with ceramic or carbon fibre rotors.
In these applications, the brakes work purely by abrasive friction, which increases in direct proportion to the increase of the pad/rotor interface temperature. Put differently, this means that the hotter the brakes get the better they work, and since the brakes on this Mustang could never get hot enough to even start working, the brake pressure only heated the steel rotors until they became glazed, thus reducing their efficiency even further.
Moreover, instead of abrading the pads to generate heat through friction, the hard-as-glass rotor surfaces merely rubbed against the pads' surfaces until the binders in the friction material started to degrade and evaporate, thus causing the outer edges of the brake pads to crumble and break away, which brings to-
In this case, the remedy was simple. We simply had the rotors ground to remove the hard outer crust, as opposed to having them machined on a brake lathe, to eliminate the possibility of causing or increasing warping, and replaced the damaged brake pads with a more reasonable ceramic formulation that worked on the principle of adhesive friction* at low temperatures.
In adhesion-based friction, some of the material that is removed from the brake pads becomes fused onto the surface of the rotors. While this layer of material is identical to the composition of the brake pads, the deposited material is constantly removed and re-deposited during braking, and depending on the brake rotor interface temperature, the braking force can increase independently of the brake pressure being applied to the brakes during prolonged braking.
As an additional step, we also used a set of dedicated brake pressure gauges to obtain actual brake force pressures at the callipers and reduced the pressure somewhat on the rear wheels to compensate for the larger and more efficient disc brakes on the rear wheels. Finally, we took the Mustang on a longish test drive to bed the brake pads in properly and handed the vehicle back to its owner with a fully functional brake system, which brings us to-
In the case study described above, the Mustang’s owner was very fortunate that the brake upgrade on his vehicle had failed as soon, and as utterly as it did. Things might have ended very badly had the brakes experienced a sudden and potentially catastrophic episode of fading at high speed, but then again, this car owner could perhaps be forgiven for thinking that all brake pad formulations work on all cars under all possible conditions.
Sadly, however, many mechanics and technicians seem to think the same thing, but when we work under tight time constraints in high-pressure professional environments, it becomes easy to overlook or ignore some safety-critical safety aspects when we service or repair brake systems. Moreover, given that very few oversights or mistakes cause fatal accidents, it also becomes easy to believe that we know everything there is to know about modern brake systems.
The fact is, however, that more than fifty per cent of passenger vehicles on our roads today are being driven with brake systems that cannot deliver optimal braking performance, despite the presence of ABS and other ADAS-based braking enhancements. One particular enhancement that comes to mind is Automatic (aka Autonomous) Emergency Braking, which will become a legal requirement on all passenger vehicles sold in Australia from next year.
One other important design feature of modern brakes that we often forget about, or perhaps have not noticed, is that braking systems have become significantly smaller, lighter, and more compact than they were a few years ago. While this is an excellent weight-saving measure, smaller brakes mean higher brake pressures, higher brake temperatures, and reduced service lives of components, all of which explain why brakes no longer last as long as they used to.
Most importantly, though, smaller and more compact brakes mean increased service intervals, as well as a greater need for us to pay more attention to the small, but critical details that make brake systems work efficiently, but more importantly, reliably. As a practical matter, we could all benefit from a short refresher course on brake system service procedures, so let’s discuss two of the most critically important details of a proper brake service, starting with-
While we are acutely aware of the fact that our customers’ budgets do not always stretch to replacing brake rotors along with the brake pads, there is no valid reason why new pads should be fitted to worn, even marginally worn, rotors. Poor contact between pads and rotors is arguably the most common reason why both brake pads and rotors overheat, which further degrades braking performance.
The fact is that once brake pads have developed localised hotspots caused by poor surface contact, such brake pads become unsafe and must be discarded. Therefore, the best way to avoid both the embarrassing comeback and the unnecessary expense is to educate our customers on the importance of resurfacing their brake rotors if they cannot replace them.
However, this writer wants to make the point that while machining brake rotors on a brake lathe is the time-honoured way to machine rotors, much better results can be achieved when rotors are ground in the same way that flywheels are. Grinding rotors, as opposed to turning them, not only provides surfaces that are closer to those of a new rotor but also surfaces that are both much flatter and more parallel than rotor surfaces that had been turned on a lathe, which makes for vastly improved braking performance, assuming that we have paid proper attention to appropriate-
Poor bedding-in or seating of new brake pads on new or resurfaced rotors ranks among the top five causes of premature brake failure, poor braking performance, and brake noise, and in many cases, the only reliable remedy for these kinds of issues is the replacement of the recently replaced brakes.
In practice, both the internet and print media abound with advice on how to seat new brake pads correctly, with the two most popular methods being the 30-50-30, or 100-30-10 procedures. If you have not heard of these procedures, here are some details-
The 30-50-30 procedure
Briefly, this procedure calls for 30 gradual stops from 50km/h, but with 30 seconds between each application of the brakes to let the brakes cool down between stops.
The 100-30-10 procedure
The procedure requires driving at 100km/h, then gradually applying the brakes to slow the vehicle down to a speed of 30km/h, and then accelerating back up to 100km/h before braking to 30km/h again. This must be repeated no more than ten times, but since this tends to overheat the brakes severely, you then need to let the brakes cool down by driving normally without using the brakes at all for several minutes after the last brake application.
It is not for this writer to say whether (or not) either of these methods are always wrong or inappropriate in all situations, but the fact is that these methods are recommended by so-called experts for all brake friction material formulations and pad/rotor combinations (and very often) without considering any of the material and crucial differences between friction material formulations.
The above paragraph is saying a lot, but we can condense it by saying that brake pad manufacture is as much as an as it is a science. Put differently, this means that while most brake pad manufacturers tend to use the same basic "recipe" to make brake pads that will work across most applications, few brake pad manufacturers use the same basic "recipe".
In fact, the list of allowable/allowed ingredients that is available to brake pad manufacturers runs to over four hundred compounds, substances, and mixtures. These include friction modifiers, binders, fillers, abrasives, adhesives, and metals like brass, zinc, copper, and even bronze that all act as lubricants. Moreover, there are no standards or legal mandates in force anywhere in the world that set or prescribe the minimum and/or maximum allowable levels of any allowed substance(s) in friction material formulations. The only exception to this rule is asbestos, which is a forbidden ingredient of friction material in most major automotive markets.
Of course, the above is not the same as saying that you never know what you are getting when you buy brake pads. On the contrary, many brake pad manufacturers produce high-quality products that guarantee consistent and reliable performance for the useful life of the brake pads. However, at the same time, there are no guarantees that any given manufacturer uses the same formulation for brakes pad intended for use in compact vehicles, and pads intended for use in heavy, high-end luxury vehicles.
It would be silly to assume that any reputable manufacturer would use the same friction material in both applications, and therefore, it would also be silly to use the same seating or bedding-in procedures for friction materials whose formulations might be as different as chalk is to cheese.
Note that in this context, we are not only referring to differences between the relative concentrations of fillers, binders, and friction modifiers in different friction material formulations. We are, in fact, mainly referring to the differences between the two most common families of friction material formulations; these being metal-based formulations and non-asbestos-based organic formulations that (sometimes) contain high levels of various ceramic substances.
As a practical matter, metal-based formulations typically work by abrasive friction, which requires exceedingly high brake temperatures to be effective. On the other hand, organic and/or ceramic-based formulations work by adhesive friction, which is usually very effective at brake temperatures of up to about 250 - 300 degrees Celsius, which is the range of brake temperatures that apply to most passenger vehicles during normal use, which begs this question-
Sadly, there is a) no single bedding-in procedure that will work equally well on all brake friction material formulations, and b) no telling to what extent an inappropriate bedding-in procedure will damage any given brake friction material formulation and/or brake rotor.
However, the upside is that this writer had found that brake pads that were bedded in strictly according to the instructions provided by the pads’ manufacturer not only last longer- they also produce less brake dust, while being quieter and more resistant to brake fade than pads that were bedded in by using rule-of-thumb methods, such the ones mentioned elsewhere.
We might also mention that a direct correlation exists between how long brake pads last and how well they work (or not, as the case may be), and their price. A good case in point involves brake pads that are supplied by this premium supplier of brake friction products; while these brake products may be more expensive than many other comparable products, these products often exceed OEM specifications in terms of fit, form, and function.
There are, of course, other suppliers and manufacturers in Australia that also supply premium brake products, but the point is that most, if not all reputable suppliers of OEM-equivalent brake friction materials offer technical support services that can advise on the correct fitment and/or bedding-in procedures for any given application.
Getting brake pads bedded in correctly is the only way to ensure reliable, consistent, and predictable operation of the brakes on any vehicle. Moreover, since the consistently reliable operation of the brake system on any vehicle can prevent accidents and save lives, crucially important aspects of a brake system service, such as ensuring that brake pads are bedded in properly should NOT be left to our customers to figure out, which leaves us with this-
It remains our collective responsibility to ensure that the brake systems on our customers’ cars work properly when we hand their vehicles back to them, which means that following rule-of-thumb brake system servicing procedures is NOT good enough.
Of course, "good enough" includes things like (among others) ensuring the callipers move freely, that all fasteners in the brake system are torque properly, and that the brake fluid is in a useable condition costs time and money. However, this is time and money that we cannot afford not to spend because few of our customers can recognise or assess to what extent the efficiency of the brake systems on their cars has been reduced or degraded over time, so the last thing we want to do is to add to this by ignoring or overlooking some basic servicing steps that could restore a brake systems’ efficiency.
