What are the basic brake components?Each component in a properly functioning brake system must work in harmony with the other components to achieve maximum braking performance. We will cover each component; it’s selection, modification, and integration into the ‘system’ as a whole. The basic components of a disc-brake system are:
- Actuator - for the driver to actuate the brakes.
- A master cylinder (MC) & reservoir – contains hydraulic brake fluid to actuate the brake calipers and a piston to move the pressurized fluid.
- Hydraulic lines – to convey the brake fluid to the brake calipers, and contain the hydraulic fluid, allowing it to be pressurized.
- Brake Calipers – located at each wheel, the brake calipers are hydraulically actuated clamps that clamp the brake pads against the rotors.
- Brake Pads – located inside the calipers, the pads are the friction material that the calipers clamp against the rotors.
- Rotors – Bolted to the axle hub or integral, the rotors slow and stop the rotation of the wheels when clamped by the calipers. They also absorb the heat created from the friction of the pads against the rotor.
How do brakes work?
- Be able to apply a force to the rotor to decelerate the wheel’s rotation so that friction is increased between tires and road and the trailer slows/stops: this ability is described as the brake system’s BRAKE TORQUE.
- Be able to create enough friction between the pad and rotors to convert the trailer’s kinetic energy to heat; this is called CLAMPING FORCE; and be large and heavy enough (the rotors) to absorb that heat without damage; this is called THERMAL CAPACITY.
What is the clamping force?
The clamping force that a caliper exerts, measured in pounds, is the hydraulic pressure (in psi) multiplied by the total piston area of the caliper (in a fixed caliper) or two times the total piston area (in a floating caliper), in square inches. To increase the clamping force it is necessary to either increase the hydraulic pressure or the caliper piston area. Increasing the coefficient of friction will not increase clamping force.
What is the coefficient of friction?
The coefficient of friction between pad & rotor is an indication of the amount of friction between the two surfaces. The higher the coefficient, the greater the friction. Typical passenger car pad coefficients are in the neighborhood of 0.3 to 0.4. Racing pads are in the 0.5 to 0.6 range. “Hard” pads have a lower coefficient but wear less; “soft” pads have a higher coefficient but can wear quickly. With most pads, the coefficient is temperature sensitive - which is why sometimes racers need to “warm up” the brakes before they work well, and also why most brakes will “fade” when they overheat – the coefficient of friction is reduced as the temperature rises. For more info in coefficient of friction, see section on pads.
What is the thermal capacity?
- Develop enough clamping force to create enough friction between pad and rotor to convert trailers kinetic energy to heat.
- Develop enough brake torque to reach the limit of traction (lockup the tires) in all conditions, and
- Have enough mass to absorb the conversion of the trailers kinetic energy to heat without boiling the fluid, warping the rotors, cooking seals, etc. And they must do both with good and consistent feel!
What are brake hydraulics?
Recall that the brake’s hydraulic system must supply movement and force. The movement must be enough to take up all slop, clearance, and deflection of parts as well as move the caliper pistons sufficiently to bring brake pads into firm contact with the rotors. The force must be enough to create enough friction between pad and rotor to stop the trailer.
What are the master cylinders?
Disc brake reservoirs are larger than those for drum brakes. You will often see two reasons given for this:
1. First, because the pistons in a disc brake caliper are MUCH larger than the tiny pistons in a drum brake wheel cylinder, disc brakes require more fluid volume to be displaced than drum brakes – requiring a larger reserve of fluid for operation.
2. Secondly, as disc brake pads wear, disc brake calipers are self adjusting. That is, the calipers only retract the piston just enough to prevent pad-to-rotor contact. Now, imagine you start with disc brake pads with ½” thick linings and you have a 4” diameter caliper piston. Every time you apply the brakes and the pads wear a little bit, the caliper retracts just a tiny bit less. By the time the pads wear to 25%, or 1/8” thick, the piston at rest will be .75” further out in its stroke than it was when the pads were new. That .75” behind the piston must be taken up by additional fluid – and in the case of a 4” diameter piston, the additional volume required is given by (pi [d/2] ^2 * 0.75) or about 8 cubic inches. Multiplied by two calipers (one for each wheel) and that’s 16 cubic inches of extra fluid reserve required to compensate for pad wear. That’s much higher than the amount required to compensate for drum brakes shoe wear. Therefore, disc brake reservoirs are larger than for drums because OEM designers must design a reservoir for disc brakes large enough that the brakes will still function even if Joe Public doesn’t check the fluid or add a drop between new pads and completely worn out pads.
It is true that disc brakes require both more pressure and more movement (volume) to operate than drum brakes.
This one can be a deal-killer. If the MC in question was designed for drum brakes and has a built-in residual pressure valve, it will not be suitable for disc/disc brakes. See section below on valve for description of residual pressure valves. For now, the point is, know the MC in question and whether or not it has built-in valve. If it does, you would have to either modify it by removing the residual pressure valve to make is suitable for use with disc brakes, or choose a different master cylinder.
The differences between disc and drum master cylinders are as follows:
1. Disc brake MC’s normally have a longer stroke and larger reservoir than those for drums
2. Drum brake MC’s have a built-in residual pressure valves.
Residual Pressure Valve
A residual pressure valve is a simple, one-way, spring-loaded valve installed either in the master cylinder. They operate by keeping a pre-determined amount of pressure in the brake lines, even with the brakes released. The internal spring determines the amount of residual pressure kept in the brake lines – normally 10 PSI. Here the use of a residual pressure valve:
10 PSI: Drum brakes only. Because drum brakes don’t use calipers and are therefore not self-adjusting there are springs installed to retract the brake shoes away from the drum. A 10 PSI residual pressure valve is used in drum brakes to keep a little pressure in the lines to balance the return-spring force so that the shoes are maintained in close proximity to the drums. Without the residual pressure valve, the return springs would retract the shoes so far from the drums that excessive pedal travel would be required before the brakes are applied.
When converting from drums to discs, you will need to remove any RPV in the master cylinder.
What is brake torque?
Brake torque in in-lbs (for each wheel) is the effective rotor radius in inches times clamping force times the coefficient of friction of the pad against the rotor. Brake torque is the force that actually decelerates the wheel and tire. There are two components – how hard the pads clamp the rotor (clamping force) and how far that clamping takes place from the center of the wheel hub. The larger the effective rotor radius, the further the clamping takes place from the wheel center, and the more torque generated by this longer “lever effect”. This is very similar to the manner in which a longer handle on a ratchet generates more torque than a short handle (for the same input). To increase brake torque it is necessary to increase the hydraulic pressure, the caliper piston area, the coefficient of friction between pad & rotor, or the effective rotor diameter.
Can you further describe brake tubing and hoses?
What is a further explanation of brake calipers?
Calipers are “floating” design. A floating caliper, common on production vehicles, has a piston or pistons only on the inboard side of the caliper. The floating caliper is mounted on pins or slides so that when the piston extends and presses the inboard pad against the rotor, the whole body of the caliper slides on its pins or guides in the opposite direction, bringing the outboard pad into contact with the rotor.
- Floating calipers are smaller, lighter, and easier to package. They are also cheap, readily available, and easy to mount.
- Floating calipers cool better as the fluid and piston are only on the inboard side of the rotor.
- Floating calipers have fewer moving parts and seals to leak or wear out.
- Floating caliper design more easily incorporates a cable-operated parking brake.
Operation of a Floating CaliperWhen brakes are applied, piston on outboard side extends in direction of red arrow until outboard pad contacts rotor. At that point, caliper slides on pins in direction of blue arrows until inboard side of caliper presses inboard pad against rotor.
What is sealing and retraction?
Caliper pistons are normally sealed with an O-ring that has a square cross-section. This O-ring stretches when the brakes are applied and the piston extends towards the rotor. When the pedal is released, the O-ring relaxes and retracts the piston. Because the rotor and brake pad surfaces are flat and aligned it takes very little movement to obtain pad-to-rotor clearance.
Apart from issues of clearance, protection from debris and damage, and ease of bleeding, there is no reason you can’t mount a brake caliper at any position around the circumference of the rotor. The 3 ‘o’ clock and 9 ‘o’ clock positions are the most common (i.e. in front of, or behind the rotor), as this affords good protection and allows the caliper to be mounted with the bleed-screw up (highly recommended), for ease of bleeding and a better proportional brake system. This is easily achieved with the DEEMAXX EXCLUSIVE 120 degree bleed screw mounting. Mounting at 6 ‘o’clock would almost certainly make the caliper far too vulnerable, rob ground clearance, and imparts no particular advantage. However, there’s no reason you can’t mount the caliper at 12 ‘o’ clock, provided you are prepared to remove the caliper (to orient the bleeder screw up) to bleed the brakes. If you do, be sure to insert a block of wood or other spacer in the caliper while bleeding.
How are DEEMAXX Rotors different?
DEEMAXX Vented –rotors are made with radial cooling passages in them to act as an air pump to circulate air from the rotor center to the outside of the rotor.
How do you care for and use brake pads?
Pads need to be clean, even, and have a high coefficient of friction against the rotor for maximum braking performance. Disc brake pads are available in an array of compounds - all claiming certain benefits. One thing that is consistent is that the pad's compound will have a different coefficient of friction depending on whether it is cold or hot. As a general rule of thumb, the following compounds exhibit the following coefficients of friction:
What does bedding-in brake pads mean?
When new brake pads are installed, they should be "bedded-in". Bedding-in brake pads is a process of breaking them in before severe use, similar to the way an engine or set of gears must be broken in.