Brake linings
are the consumable surfaces in brake systems, such as drum brakes and disc brakes used in automobiles asbestos brake linings.
Fig 1.24: Brake liner (Ferodo 2629 F) for drum brake
Since the lining is the portion of the braking system which converts the vehicle's kinetic energy into heat, the lining must be capable of surviving high temperatures without excessive wear (leading to frequent replacement). A Fig 1.24 shows the brake lining Ferodo 2629 F material.
1.14.1. Structure of brake linings:
Brake linings are composed of a relatively soft but tough and heat-resistant material with a high coefficient of dynamic friction (and ideally an identical coefficient of static friction) typically mounted to a solid metal backing using high-temperature adhesives or rivets.
The complete assembly (including lining and backing) is then often called a brake shoe (or lining) in case of drum brake, but in disc brake it is an individual and name brake pad. The brake lining is that part of the brake pad which actually contacts the metal brake disc (rotor) when the brake is engaged.
The lining has to be tough. During hard braking, the shoe may be pressed against the drum by force of 4500 N or higher. Since friction increases as the applied force increases, a strong frictional drag is produced on the brake drum. This produces the braking effect at the' wheel.
The braking linings are attached with shoe brakes by synthetic resin adhesives or and by riveting.
1.14.2. The usual advantages of synthetic resin adhesives lining due to following reasons:
Absence of riveting holes.
More contact surface.
Free from scoring action.
More effective wearing thickness.
1.14.3.
There are of two main varieties (of brake lining):
1. Solid -woven type
2. Moulded type
1. Solid -woven type:
The asbestos -base non-metallic linings have in general, an average coefficient of friction of 0.4 up to around 260° C and fade is not serious up to 300°C. Their maximum temperature resistance is around 350°C.
A further improvement is the zinc wire inclusion.
Zinc serves to conduct some heat away from the working surface and so reduces slightly the maximum temperature reached by the particular brake mechanism. Zinc -wire linings have also better anti -fade characteristics and resistance to wear than the non-metallic type.
2. Moulded type:
This type is moulded directly from the "mix", which contains asbestos fibres, together with resin powders and fillers. The average coefficient of friction with this type of linings is 0.4 and temperature resistance varies from 400° to 450°C. They have good anti -fade and anti-wear characteristics.
Types of moulded friction material for brake linings
:
(i) Ferodo 2629 F
friction material – for drum brake lining shoe.
(ii) Ferodo 2449 F
friction material – for disc brake pad.
(i) Ferodo 2629 F:
-
This is for use on drum type brakes. It is fawn in colour, having random fibre asbestos base and containing while metallic particles
(Fig. 1.24).
Recommended operating range:
Unit pressure 70-690 kN/m2
Maximum rubbing speed 18m/sec
Maximum temperature 400° C
Maximum continuous temperature 175° C
Bonding Common adhesives may be used for bonding, but for better results thermosetting adhesives should be employed.
Recommended mating surface: - Good quality, fine grained cast iron. Cast steel is not suitable as a mating surface, but forged or cold rolled steel with a Brinell hardness of 200 or more may be used.
(ii) Ferodo 2449 F: -
This rigid moulded friction material is for disc brake pads for cars. It is light brown in colour, having a random fibre asbestos base and containing copper particles. The material has good resistance to fade and to wear. Ferodo 2449 F is only supplied integrally moulded to steel back plates in specified sizes (Fig. 1.25).
Recommended operating range:
Unit pressure 0.35-5.2 MN/m 2
Maximum rubbing speed 24m/sec
Maximum temperature 550° C
Maximum continuous temperature 250°C
Recommended mating surface:
Good quality fine grained pearlitic cast iron. Cast steel is not suitable but forged or cold rolled steel with a Brinell hardness of 200 or more may be used.
When the lining is worn out, the backing or rivets will contact the rotors or drums during braking, often causing damage requiring re-machining or replacement of the drums or rotors. An annoying squeal caused by the warning tang is the typical alert that the pads need to be replaced; if the squeal is ignored for too long, drum or rotor damage (usually accompanied by an unpleasant grinding sound or sensation) will be the typical result.
The lining may also become contaminated by oil or leaked brake fluid. Typical symptoms will be brake chatter, where the pads vibrate as the lining grabs and releases the rotor's surface. The solution is to repair the source of the contamination and replace the damaged pads.
The brake pads are made of T -section and are curved to match the surface curvature of the disc. The expander end of the pad is called the 'toe' and the anchor end is termed the 'heel'. The ends may be flat, curved or have a semi-circular groove to locate the expander or anchor. They are made of cast iron or steel. The modern vehicles employ pressed steel brake pad. The dynamic friction coefficient "µ" for most standard brake pads is usually in the range of 0.35 to 0.42. There are some racing pads that have a very high µ of 0.55 to 0.62 with excellent high temperature behavior.
Fig: 1.25: Brake pad (Ferodo 2449 F)
Brake pads must always be replaced simultaneously on both ends of a vehicle's wheel, as the different pad thicknesses (and possibly material types) will cause uneven braking, making the vehicle pull in the direction of the more effective brake. For most vehicles, replacing pads is very easy, requiring a minimum of tools and time. Pads and lining are designed to be consumable and should therefore be easy to service.
Are brake pads and shoes the same thing?
Most modern cars these days have either disc brake systems (also known as rotors) or a drum brake system. Disc brakes and brake pads go together whilst brake drum systems use brake shoes to create stopping power. So, the short answer is no – brake pads and brake shoes are not the same thing.
Disc and drum brakes also work quite differently to achieve the same goal, which is to effectively slow down and stop your car. While they both use friction material, each type of braking system uses various components to execute this, which means they aren’t interchangeable either.
If you’re unsure what type of brakes your car has, read on to find out more.
Natrad has a large range of quality Mintex and Nisshinbo brake parts for a wide variety of vehicle types.
What are the different types of brakes?
There are 2 types of brakes typically used in cars today. The first, is disc brakes which are commonly found in modern and high performance vehicles. The second are drum brakes typically found in older cars.
High performance vehicles or sports cars have a disc brake system that often comes with ventilation holes or slots for enhanced heat dissipation. Discs work together with brake pads, which are a part of the caliper assembly.
Secondly, there are drum brakes. These brakes are more outdated and typically can be found in smaller or older cars, or coupled with a pair of disc brakes. For example, a hatchback might have front disc brakes and rear drum brakes. Brake shoes are used instead of pads, which sit inside the drum and apply pressure during braking.
While disc brakes are more common, plenty of cars still utilise a mixture of both kinds.
Not sure which type(s) of brakes your car has? Next time you’re heading out for a drive, you can check your wheels. Some cars have complex rim designs which make it hard to see what’s behind, but usually you should be able to view some part of the braking system – whether it be the caliper assembly, disc, or drum.
Disc brakes look like a flat cylindrical disc, hence the name. You may be able to see the caliper assembly attached on the outside (see below for reference).
Drum brakes however, look more like a casing. Inside they hold brake shoes and various other smaller components that help create the friction needed to stop. See below for comparison:
How do braking systems work?
Your vehicle’s braking system makes use of friction and hydraulic pressure in order to stop your wheel spinning and halt your car.
So, how does the system do it? Let’s look at disc brakes as an example.
The overall braking system is made up of various parts aside from the brake disc itself. Parts include:
Brake fluid
Master cylinder
Caliper assembly (multiple components)
Piston
Brake pads (2 per disc)
And brake disc
Brake fluid circulates the system, so when you press the brake pedal – hydraulic pressure is applied. The sequence goes a bit like this:
Press brake pedal
Caliper assembly receives high pressure brake fluid from the master cylinder (hydraulic pressure)
Caliper pushes piston
Piston presses against the brake pads
Brake pads are squeezed against the brake disc
The friction from the brake pads pressing against the disc decelerates the motion and stops your wheel from spinning.
While brake pads press inwards on the brake disc, brake shoes work the opposite way. They sit on the inside of the brake drum (while attached to a backplate assembly).
When hydraulic pressure is applied, they press outwards against the drum to create friction and stop the car.
Troubleshooting brake pads vs brake shoes
Have you heard squealing noises from your brakes recently? You might need new brake pads or shoes. As friction material wears over time, most brake pads and shoes have wear indicators which screech when low. If you’ve heard this sound, replacing brake pads or shoes will help.
Friction material is made to wear so replacing pads and shoes is completely normal. However, it’s important to do so regularly according to your servicing schedule, or you risk getting into dangerous collisions with underperforming brakes.
Think you might need new pads or shoes? Just nip into your nearest Natrad AutoCare where our qualified technicians can inspect, diagnose and replace any system parts.
Our range of industry leading Nisshinbo and Mintex brakes are available from workshops across the country. Find your nearest store here.