Truck Brake System

How? Why? Truck Calipers Are special?

"No Engine Brake." Have you ever won­dered what this sign means when you pass it on the highway?

A truck's engine brake is also known as a­ compression brake system. Sometimes it's called an engine retarding device. Retarders are especially helpful for truckers on mountain downgrades.

But how do retarders work? The compression stroke is one part of an engine's four-cycle system. The intake and exhaust valves are closed as the piston moves up, compressing the air being forced into the brake cylinder. At the top of the stroke, fuel enters the very hot air, burning rapidly and pushing against the piston, which is on its way back down. When the piston begins its ascent, the exhaust valve opens to emit the spent gasses.

Suppose that the valve is popped open when the piston is just past the top center, as the compression­ stroke is ending. The compressed air is allowed to escape. Then the intake valve lets in more air, and the piston begins to compress it. At that point, the engine becomes an air compression device, with gravity providing the energy needed to run it [source: Newbie Driver].

As the compressed air escapes, the truck makes a backfiring or popping sound. Although more modern systems make less noise, the perception remains that a truck should rely on the air brake system.

Now, let's roll on to take a closer look at how truck and automobile brakes differ.How Are Truck Brakes Different From Car Brakes?

Let's ­begin by considering the ways that truck and car brakes are al­ike. The purpose of bra­kes on all types of vehicles is to stop them. Brakes on both trucks and cars work on the principle of friction. Both kinds of vehicles have brake drums, along with their pads and shoes, connected to the vehicles' wheel axles.

Car brakes rely on the brake fluid that flows through the system to work properly. Thus, car brakes are ahydraulic system, relying on fluid. On the other hand, truck brakes depend on compressed air. (Trains and buses also use this type of brake system.)

A major plus to using air is that it never runs out (as brake fluid can). This means that the air brake system is very reliable -- even if there's a small leak somewhere in the system, it always works.

Most of the newer heavy trucks use a dual air brake system that is not available on automobiles. A single set of brake controls works both of these separate air brake systems. If one system fails, the other will work.

The flaw in the compressed air system of trucks isbrake lag. That's the time it takes for air to get through the lines and force the linings to contact the drum. When they push the brake pedal, drivers must get used to the fact that air brakes don't work at once, as they do on a car. Lag time is less than a second, so this is not a major problem.

The truck's air braking system has several tasks. First, it keeps up a steady supply of compressed air. In addition, it must direct that air's flow. Finally, it uses the energy of air pressure and changes it into mechanical force.

One, two, three! A truck's air brake system is really made up of three different brake systems. Let's investigate each of them.

Truck Brake Types

Service brakes are used during normal driving. A seque­nce of events occurs when a driver pushes the brake pedal.

Air moves into a brake chamber through airlines.

The air forces out a pushrod.

The pushrod pushes the slack adjuster.

The camshaft turns.

The turning of the camshaft twists the S-Cam. (You guessed it -- it's called S-Cam because it's in the shape of an S.)

The brake linings are forced to contact the brake drum.

The driver activates the parking brakes by pulling out one or both of the valves on the dash. (Tractor brakes have a yellow button; trailer brakes have a red button.) The dash button releases the spring inside the brake chamber, thus beginning steps 3-6 listed above.

The emergency brake system uses parts of the other two systems to stop the truck if brake failure takes place [source: Newbie Driver].

Inside the brake chamber is a powerful spring with about 2,500 pounds of pressure behind it. That spring is held back by a steady and constant airflow in the chamber. The emergency brakes deploy automatically if there's not enough air in the system to hold the spring back. If air pressure drops below 60 pounds per square inch, the low-pressure light comes on. A buzzer may also sound.

Not everyone is happy with the way that S-Cam brakes work. A recent innovation is the use of disc brakes. Let's head down the highway to see how disc brakes work on trucks.

Some trucks have disc brakes instead of S-Cam brakes. Air pressure works on the brake chamber and the slack adjuster in the same way that it does in S-Cam brakes. However, a power screw replaces the S-Cam. The power screw is turned by t­he pressure on the brake chamber and the slack adjuster. Then the power screw grasps the disc or rotor between a caliper's brake lining pads.

The many benefits of air disc brakes include the following:

Compared to drum brakes, air disc brakes reduce stopping distances by almost 40 percent. Because pressure is continually applied, it's easier for the vehicle to come to a complete stop.

Air disc brakes almost completely stop brake fade.

Air disc brakes don't increase the wear of brake linings on a trailer or disc pads on a tractor.

Still, despite all of the advantages, change isn't always embraced by the masses. In the United States, no regulation demands the use of air disc brakes, which are viewed as a high-end item because they're about twice the cost of drum brakes. Currently, about 95 percent of the U.S. heavy-duty truck market relies on drum brakes. In Europe, more than 80 percent of commercial trucks already use air disc brakes. The complete shift to air disc brakes may require 10 to 15 years.

They say that a picture is worth a thousand words. Let's cruise to the next page to get a glimpse of a diagram of a truck's braking system.

Source

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     HMF Is a Company with experience, which manifactures and distributes Truck Spare Parts and passanger cars too. HMF's brand: CONTINUAL ( quality assured ISO 9001:2008 brand ) we have accumulated our basic capital, namely professional knowledge and experience which we consider as guarantee of our success. We supply production, distribution and sale of BRAKE CALIPER repair kits for trucks (such as Mercedes, Volvo, Daf, Scania, Iveco,Renault, Mercedes Sprinter, passenger cars etc)

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 There are some car problems you simply shouldn't ignore. Brake problems are perhaps chief among them. A car that can't stop, or has trouble stopping, is dangerous for the driver and everyone else on the road. That's why it's important to keep all parts of your brakes in proper working order.

First, let's talk about brake calipers and what they do. On a disc-brake-equipped car, the caliper sits over the brake rotor(the circular metal disk inside your wheel) like a clamp. Inside the caliper is a brake pad, a small block of friction material backed with a metal plate. When you step on your brake pedal, pistons inside the caliper cause it to apply pressure to the brake pad which squeezes the rotor, causing the car to slow or stop.

That's the idea, anyway. But if one or more parts of your brake calipers aren't working correctly or if they're installed improperly, you could experience trouble with stopping. When you're performing work on your brakes, you have to ensure there aren't any problems with your caliper guide pins.

The caliper guide pins are two round metal pins on each brake caliper where the brake piston assembly sits. They're called guide pins because they're responsible for guiding the proper angle for how the brake pad meets the rotor.

If you're having issues with your brakes, the culprit could be the guide pins, but a careful inspection is the only way to know for sure.

When you're changing your brake pads yourself, part of the job will be removing the guide pins. But what happens if you put the pins back improperly? Then you could experience noises or problems stopping. The brakes could stick or grab when you're driving, or you could hear a grinding noise if the calipers aren't meeting the rotor at the proper angle.

So how do you know if the guide pins are at fault? You'll need to inspect the brakes like you're about to change the pads. In fact, it's a good idea to check the pins whenever you're changing the pads yourself. Lift the car, remove the tires, take the caliper off and look at the caliper housing. See those pins at the top of the housing? Those are the guide pins. Most cars have two guide pins with a rubber housing surrounding each [source: Dan's Garage].

Problems to look for include caliper pins that are corroded, or ones that aren't properly lubricated. Also, the pins could be stuck in the rotor or they won't go in all the way after the pads have been replaced.

The pins should be easy to take out with a screwdriver and a few light taps from a hammer. Caliper pin removal tools are also available at auto parts stores. If the guide pins are really stuck in there, or if they're rusted in place, you may have a problem on your hands. In that case, you'll need to find an experienced mechanic to discuss your options.

Before we re-insert the caliper guide pins into the caliper housing, they need to be properly lubricated. But remember, it's always best to check your vehicle's service manual before doing this kind of work.

You're going to need some high-temperature grease. This is a synthetic lubricant designed for machinery that can withstand temperatures of several hundreds of degrees Fahrenheit. Brakes generate a tremendous amount of heat because they're essentially a piece of metal used to slow down another piece of metal moving at highway speeds. The last thing you'll want is for the lubrication on your brake caliper pins to be unable to take the heat.

First, thoroughly clean the brake caliper guide pins, removing any excess grease or dirt leftover from when they were inside the caliper. Coat them in a layer of the high temperature grease. From there, you can re-insert the pins back into the caliper housing. They should slide right in if you used enough grease. Once those are back in place, you can complete the rest of your brake work -- like replacing the pads and reinstalling the caliper.

Some auto repair shops will skip the step of lubricating the guide pins. But while some say it's not essential, it's a good step in keeping your brakes operational and making sure they can stand up to the wear and tear they'll face on the road.

Source

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