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Drum Brakes: The Beat Goes On
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By Counterman
link hidden, please login to view announced the introduction of its link hidden, please login to view, which it said is a premium lineup of purpose-designed brake pads for the commercial vehicle segment features five customized formulations, including link hidden, please login to view and link hidden, please login to view. “Each design offers advanced friction technology to deliver a premier level of performance matched to vehicle usage,” the company said. The program will be available in early 2025 to meet the automotive needs of the underserved commercial and fleet market, and is on display at AAPEX, at the Mevotech booth #A3038.
“We’re excited to launch the TTX Brakes category, showcasing our commitment to the design and development of products customized for the individual needs of high-usage commercial vehicles and working trucks. As a brand, it’s an important milestone in expanding our TTX product category that has become synonymous with extreme strength and durability for a market segment that relies on optimal performance without compromise,” said Todd Hack, EVP sales and marketing, Mevotech.
Mevotech said all TTX Brake pads come with a comprehensive installation kit to facilitate a more seamless install that saves up to 30 minutes. Installation boxes include caliper mounting hardware.
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By Counterman
link hidden, please login to view announced a new addition to its Galvanized Brake Pad lineup. The new part introduction covers over 630,000 vehicles on the road, the company said. The company added that the brake pads are built using
link hidden, please login to viewGalvanized steel and incorporate O.E. specified Mechanical Fusion Technology. link hidden, please login to view New Part Number(s) & Vehicle Compatibility: NS2304
Expanded coverage includes the following vehicle models: Lexus: RX350 (2023), RX350H (2023-2025); Toyota: Highlander (2020 – 2024), Grand Highlander (2024-2025).
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By Counterman
The success of any new technology is often weighed and determined by the associated pros and cons.
In the case of electronic parking brakes (EPB), technology wins, and we’re going to look at why. Of course, that doesn’t mean there aren’t purists who would rather die than give up their manual parking brakes, so we’ll also have some fun and work in a shout out to old-school for the advantages that many people still like.
To paint a clear picture and fully understand EPBs, we have to look at the lineage that led up to them. Traditional parking brakes were simple. There are four different methods of engagement that come to mind.
One, the old-school foot pedal on the left kick panel on just about every American car for as long as you can remember. Step on it and the brakes are engaged. Pull the nearby lever to release the pedal.
Two, the occasional use of a swing-lever in the same location that you pull upward 90 degrees to engage and push back down to disengage.
Three, a T-handle near the center of the dash that you pull straight out with your right hand to engage, twist the handle to release.
And four, what ultimately became the most popular: a hand lever between the seats. Pull it up to engage the parking brake; push the button on the end to release.
Take any of these engagement levers, hook them to a series of cables, connect the cables to the brakes and you have a parking brake. On rear drum brakes, the cables connect to a lever – sometimes inside the drum, sometimes protruding through the backing plate – then the lever mechanism acts to push the shoes into the drum. On rear disc-brake systems, the cables connect to a lever on the brake caliper. The lever transfers a rotational motion to an internal mechanism that pushes the piston out, clamping the pads to the rotor.
On all these systems, what keeps the parking brake engaged is the mechanical aspect of the engagement lever: a pawl that engages a series of teeth. Spring tension keeps pressure on the pawl, creating the telltale ratchet-clicking sound of a parking brake being engaged.
Drawbacks of Manual Parking Brakes
Manual parking brakes worked, and they worked well. But they had drawbacks. The big one was the cables. They wore over time, and they were subjected to the elements, eventually corroding in one form or another, causing them to stick, bind or break. They required occasional adjustment due to stretching, and they also were susceptible to snagging things on the road should you run over a large object.
Another drawback came from the mechanisms. They were designed and positioned in the vehicle to take advantage of leverage from your arm or leg to engage the parking brake. Considerable strain is put on them – more than meets the eye – and over time not only do the mechanisms wear, but occasionally so do their mounting points – resulting in sloppy, undependable operation.
These drawbacks immediately shed light on the initial benefits of an EPB.
Basic Types of EPB Systems
An EPB is set through a simple switch, which sends a signal to the control unit that parking-brake engagement is requested. Not only does this save a lot of space in the cabin by eliminating any type of engagement mechanism, but it also eliminates all the associated wear characteristics. So, how does an EPB work? There are two different types
of systems.
The first utilizes an electric motor and mechanical actuator that’s mounted underneath the vehicle. The actuator is connected to traditional cables that in turn are connected to either the drum or disc brakes. The problem with this type of system is the drawbacks associated with cables.
The second type of system utilizes a motor and geartrain attached to or incorporated into the brake caliper – eliminating all cables – making it the most common EPB system in use today. The concept of an EPB is simple. It’s not difficult to understand how they work, but it’s their benefits that tell the real story.
The mechanical benefits include not only space savings in the cabin, but also elimination of wearing mechanical components, weight savings, no regular adjustments and they’re easier to apply. It takes no effort to push a button.
The functional benefits of an EPB include a hill-assist function that keeps the car from rolling backwards on a hill start; automatic release when the car is put in gear (although this function was built into some manual parking brakes via a solenoid that released the parking-brake pedal); and automatic engagement as an anti-theft device.
You may get questions about replacing brake pads on a vehicle equipped with an EPB. Most vehicles require a scan tool to retract the parking-brake mechanism inside the caliper, and it’s usually referred to as service mode. This is considered a drawback by some, especially for a DIYer, since not everyone has a scan tool handy. Drawback or not, when working on an EPB, always follow the manufacturer procedures. Never try to push a piston back using any different method or you risk damaging the gears or motor in the caliper.
For those of us who have a scan tool and who have fought countless manual parking-brake calipers turning and pressing the piston with special tools – not to mention fighting binding brake cables – service mode and EPBs are a welcome technology.
Handbrake Turns and Other Neat Stuff
EPBs are easy to work on and do neat stuff, but it’s time to throw the manual parking brake a bone. From a service standpoint, the systems are entirely mechanical. It’s all right in front of you. No scan tool required, no trouble codes, no poor wiring connections – no headaches! Now let’s talk about driving the car.
Have you ever seen a movie or TV show with a car chase, where the car slows down, and the next thing you know it whips a U-turn practically in place? Popular slang calls it an end-around; more officially it’s known as a handbrake turn. It’s done by turning the wheel and engaging the parking brake.
One reason a hand lever between the seats became so popular is you can easily use it for this purpose by holding the button in and pulling up on the lever to engage the brake. You never release the button; just work the lever
to get the intended brake pressure, and when you come out of the turn, let the lever return to its rest position.
This tactic is employed regularly by drivers in certain types of racing, allowing them to make their car handle
in an intended manner.
Experienced drivers know how to capitalize on it, and different techniques yield different results based on whether you turn then engage the brake, or engage the brake then turn. You also can change the control aspects by how hard you engage the parking brake.
Mastering the art of the handbrake turn is an irreplaceable aspect of performance driving, whose roots stem from days when racing or eluding the law was commonplace on back-country roads. If you wonder how it’s done on old American iron that features a foot pedal for parking-brake engagement, there’s a trick to that too. They disable the pawl engagement of the pedal, so you can gain the same control and feel with your left foot without the brake locking on, and there’s another advantage: You can keep both hands on the wheel.
The feel – a physical connection, if you will, between driver and car – is not something you can do with an EPB, which is why many purists prefer a manual parking brake. Of course, scarcely a car is made today with manual parking brakes. The EPB is both a safety and convenience feature, controlled by the antilock-braking and stability-control systems. And EPBs typically provide greater holding power. For cars not originally equipped, EPB conversion kits are becoming more popular by the day.
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By Counterman
Bleeding the brakes is a procedure that’s performed to remove air from the system when a component is replaced, and one that’s performed strictly from a maintenance standpoint of flushing or changing the brake fluid. The telltale symptom of air in a brake system is a soft or “spongy” pedal, along with poor brake performance.
The idea and basic process is generally understood: You must get all the air out for the brakes to work properly. Air compresses and fluid does not, so even the tiniest amount will affect brake operation. Bleeder screws at each wheel allow the air to be forced through and out. If the idea sounds simple, it is, but it’s not without the occasional headache.
The key is that not every system responds the same, and you may need to bleed one differently than another. There are a few different methods you can use, and while it often comes down to preference, it pays to be familiar with them all.
The most important thing, however, is your mindset. Don’t think about brake work and bleeding as two different things. Instead, when performing any brake work, think ahead about bleeding and prepare for it. It always should be a part of brake work, as opposed to leaving it as an afterthought.
At minimum, brake fluid should be replaced/flushed every two years. The older it gets, the more moisture it absorbs, the worse it performs and the more corrosive it gets – slowly eating away at the expensive internal components of a brake system. When replacing brake pads, the caliper pistons must be pushed back into
the caliper.
The most common practice is simply to push them back with whatever tool you have at your disposal and remove any excess fluid from the master-cylinder reservoir, but this isn’t the best way to do it. The proper way is to open the bleeder screw prior to pushing the piston back in and let the old fluid be pushed out.
When you force it back into the master cylinder, you’re forcing contaminants and particles back past the master-cylinder seals, which can potentially damage the seals and lead to premature failure. In short, if you’re working on the brakes, get that old fluid out of there!
Bleeder Screws First
The first thing I always do with any type of brake work is check all the bleeder screws and make sure they open. If they’re stuck, regardless of what needs to be done to loosen them – be it heat, penetrating oil or another form of persuasion – now is the time to do it. If you ultimately have one that breaks, you can plan to replace that component as part of the job, instead of waiting until the end only to have one break when you’re
almost done.
Once you’ve opened the bleeder screws, take the additional step of removing and cleaning them. Spray brake cleaner into one end to make sure they aren’t plugged up with dirt or rust. Be sure to wear safety glasses – it often sprays back in your face if they are. Brake fluid should also drip out of the caliper or wheel cylinder, so be prepared with a drain pan underneath. It may not be a lot, but you should see at least a little fluid.
It’s not so important at this step that a lot of fluid comes out, but make a mental note of it. If no fluid comes out, there may be blockage in the caliper or wheel cylinder. It’s not uncommon for rust to form in the bleeder port and keep anything from coming out, even with a clean bleeder screw. If you run across this, it’s a problem that’s easily remedied using a small pick to poke through the rust.
Once you’ve confirmed that all bleeders open and fluid can flow, you’ve set the stage for a successful bleed of the system – but make sure you haven’t overlooked any bleeder screws. Most vehicles have four (one at each wheel). Some four-piston calipers have two bleeder screws each – one on the inboard side and one on the outboard. They both need to open.
Occasionally you may run across a vehicle with a load-sensing proportioning valve in the rear (usually on trucks) that has an additional bleeder screw on top. This can really throw you for a loop because they’re often out of sight. If you don’t bleed the air at this location, you’ll never get a good pedal. The bottom line is to locate all bleeder screws, and make sure they all open and flow freely.
Bleeder screws are located at the high point of a brake caliper, but it’s possible to install some calipers on the wrong side. This is a very common mistake and when it happens, the bleeder screws will be on the bottom. It’s impossible to bleed the system like this, so if you run across it, you’ll have to remedy the situation beforehand.
The ‘Standard’
“Pump it up and hold it!” For most of us, our experience bleeding brakes began as a helper. You pump the brake pedal a few times and hold it. Then the person doing the work opens a bleeder screw. When the pedal reaches the floor, you report “on the floor.” The bleeder screw is then closed, and the process repeated until all air is forced from the system, and you report a good solid pedal.
To properly perform the procedure, you start at the bleeder located furthest from the master cylinder, then finish with the bleeder closest – in other words RR, LR, RF then LF. This method, often referred to as “manual” bleeding, has been the standard procedure for many years, and most likely always will be. It works well most of the time and requires no special equipment.
The drawbacks are that it can be time-consuming and requires a helper, which we don’t always have. You also must make sure you don’t run out of fluid in the process, or you’ll be starting all over again.
The Master Cylinder
Brake master cylinders must be “bench”-bled prior to installing them. Most master cylinders come with a kit of hoses and fittings to connect to the outlet ports. The hoses are then run back to the filled reservoir. With the master cylinder secured in a vise, you can access the piston and use a tool to push it in to fully depress it, which forces the air out and up into the reservoir.
There are many reasons to do this. For one, many master cylinders are mounted at angles that can trap air and make bleeding on the car extremely difficult. Secured level in a vise eliminates this problem. It’s also much quicker. Usually, it only takes five to 10 short strokes to get the air out. When the cylinder is mounted in the car, it takes the full travel of the brake pedal for the same short stroke. It also saves fluid by recirculating it back into the reservoir.
The most important thing to remember is that air can still get trapped in the master cylinder during installation. Usually, it’s forced through the lines and out, but not always. If you’ve bled the brakes and still have a low or soft pedal, you may have air in the master cylinder. At this point, it’s easy to get out. With an assistant holding pressure on the pedal, crack the line fittings at the master cylinder. You’ll hear the sound of the air as it’s forced out. Some master cylinders have bleeder screws for this purpose.
Gravity Bleeding
Gravity bleeding is often overlooked, since the “standard” method over the years has a stronghold on the perception of brake bleeding. Gravity bleeding is simple: Fill the reservoir and open the bleeder screws. Sit back and relax. Gravity will pull the fluid through the system, and the air will travel along with it and out. When fluid continuously drips from the bleeders, your job is done. Theoretically speaking, gravity bleeding should always work, and it usually does.
Truth be told, I rarely use any other method. The problem with gravity bleeding is it can be slow. I usually let gravity do its thing as I clean up from the job. After I get fluid from each bleeder, I close them, pump the pedal a few times to seat the brakes, then open them one more time to release any remaining air. It’s almost foolproof.
Pressure Bleeding
Pressure bleeding is popular among professional technicians due to the speed of it, and the fact that you don’t need an assistant. The drawback is the equipment can be expensive, so you must use it all the time for it to pay for itself.
A pressure bleeder utilizes an adapter that attaches to the master cylinder, then forces fluid into and through the system. The main advantage to pressure bleeding is that it’s quick, but sometimes it’s also necessary. This is especially true on some newer vehicles with antilock braking systems (ABS). Air can get trapped in the ABS valving, and in some situations, pressure bleeding is the only method that will work. The high pressure compresses the air bubbles to the point where they’re carried through with the fluid, instead of hanging up in a crevice while the fluid flows by.
If you work on newer vehicles, at some point you will need a pressure bleeder. A final advantage to pressure bleeding is this equipment stores a volume of fluid, so you don’t have to worry about running out mid-process.
Vacuum Bleeding
A vacuum bleeder attaches at each bleeder screw and draws the fluid through the system. It’s just another way of doing it with the advantage of speed when compared to manual bleeding. Vacuum bleeding also is one of the cleaner ways to do it because you’re drawing the fluid through the system directly into a container. You don’t have to worry about catching the fluid that’s pushed out of the bleeder using other methods.
Auto-Refill Kits
It’s easy to run out of fluid when bleeding brakes. We’ve all done it. A popular option for manual, gravity or vacuum bleeding is a refill kit that connects to the master cylinder and feeds fluid into it through gravity. They usually have a large enough capacity for bleeding or changing the fluid. Are they necessary? No, just a convenience.
Final Tips
Some newer vehicles with ABS have the option to bleed the ABS modulator and valve assemblies with a scan tool. This uses the ABS pump to force fluid through the system. The advantage is getting air out of the modulator. This often is the quickest and most efficient way to do it, but generally it’s not mandatory if you don’t have the scan tool to do it. The same result can be had with a pressure bleeder.
There are two things that are frequently confused – a soft pedal and a low pedal – and it takes experience to recognize the difference. A soft pedal is caused by air in the system, and a low pedal is commonly caused by misadjusted drum brakes, so just be aware of this and don’t confuse the two. With the proper preparation and a little bit of patience, brake bleeding always should be the most routine part of the job.
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