Brake pads are also called brake skins. In the braking system of a car, brake pads are the most critical safety part, and they play a decisive role in all braking effects.
The principle of brake pads
The working principle of brakes is mainly from friction, using the friction between brake pads and brake discs (drums) and tires and the ground, converting the kinetic energy of vehicle travel into heat energy after friction, and stopping the car.
A good and efficient brake system must be able to provide stable, sufficient and controllable braking force, and have good hydraulic transmission and heat dissipation capabilities to ensure that the force applied by the driver from the brake pedal can be fully and effectively transmitted to the master pump and each sub-pump, and to avoid hydraulic failure and brake recession caused by high heat.
The braking system in a car is divided into two categories: disc and drum, but apart from the cost advantage, drum brakes are far less efficient than disc brakes, so the braking system under discussion will only focus on disc brakes.
Composition of brake pads
The brake lining is generally composed of a steel plate, a bonded thermal insulation layer and a friction block. The heat insulation layer is made up of non-heat transferring material for the purpose of heat insulation.
The friction block is composed of friction material and adhesive, which is squeezed on the brake disc or brake drum to produce friction when braking, so as to achieve the purpose of vehicle deceleration and braking.
As a result of friction, the friction block will gradually be worn out, and generally speaking, the lower the cost of the brake pad, the faster it will wear out.
When the friction material is used up, the brake pads should be replaced in time, otherwise, the steel plate and the brake disc will be in direct contact, which will eventually lose the braking effect and damage the brake disc.
Classification of brake pads
●Brake pads for disc brakes
●Brake shoes for drum brakes
●Lining pads for large trucks
How to care for brake pads
Brake shoes, commonly known as brake pads, are consumables that will gradually wear out in use and must be replaced when they reach their limit, otherwise they will reduce the effect of braking and even cause safety accidents.
Brake shoes are a matter of life and safety, so they must be treated with care.
Under normal driving conditions, brake shoes should be inspected once every 5,000 kilometers, not only to check the remaining thickness, but also to check the state of shoe wear, whether the degree of wear on both sides is the same, and whether the return position is free, etc. Abnormal conditions must be dealt with immediately.
Brake shoes are generally composed of iron lining and friction material, do not wait until the friction material is worn out before replacing the shoes.
For example, the Jetta (Gallery Forum) car front brake shoes, the thickness of the new piece of 14 mm, and the limit of the replacement thickness is 7 mm, which includes more than 3 mm of iron lining thickness and nearly 4 mm of friction material thickness.
Some vehicles have a brake shoe warning function that will alert the meter to replace the shoes once the wear limit has been reached.
Reach the use limit of the shoes must be replaced, even if still can be used for a period of time, will reduce the effectiveness of braking, affecting the safety of driving. Only in this way can the brake pads and brake discs have the best braking effect and the least wear. ¸
When replacing the shoes, you must use a special tool to jack back the brake distributor pump. You can’t use other pry bars to press back hard, this will easily cause the brake caliper guide screw to bend and make the brake pads jammed.
After replacing, be sure to apply the brakes for a few feet to eliminate the gap between the shoes and the brake disc, causing the first foot to have no brakes and prone to accidents.
After replacing the brake shoes, it needs to be broken in for 200km to achieve the best braking effect, and the shoes just replaced must be driven carefully.
Brake pad replacement method
As the saying goes, “If you want to be good at what you do, you must first be good at what you do.”
To save money on brake pad replacement, we must prepare a set of suitable tools.
To replace the brake pads, we will use a jack, a suitable socket wrench, a plum wrench, a screwdriver, sandpaper and grease.
Some tools are usually provided by the vehicle, such as a jack and across socket for removing tires; while some need to be purchased on your own. All tools and brake parts can be purchased online.
Once we have all the tools and parts, we can start replacing the brake skins.
We can loosen all the wheel bolts by half a turn, no need to unscrew them completely.
Before lifting the vehicle, it is easier to loosen the wheel bolts by using the friction between the tires and the ground, which is why we do this as the first step.
In the second step, we use a jack in the lifting position of the vehicle to jack up the side of the vehicle.
Vehicle lifting position is dedicated to lifting the vehicle body parts, generally located behind the front wheels and the rear wheels in front of the body “beam”.
The vehicle lift position will generally have a palm-sized raised rubber pad, easy to touch with your hand to feel.
We simply lift the vehicle until the wheels that need to be replaced are slightly off the ground.
Then we can unscrew all the wheel bolts and remove the wheel. Some vehicles with aluminum wheels have a unique wheel structure that allows the wheel to remain stuck on the wheel’s oscillating bearing after the bolts are removed.
If we encounter the above situation, we can try to use our feet to tuck in the upper edge of the tire sidewall or use our hands to tap the front and rear edges of the tire sidewall inward in turn, which will help the tire to come off.
Remove the wheel against the brake disc below to prevent the hydraulic jack from releasing pressure and causing the vehicle to fall over causing injury or death.
The brake distributor pump of the disc brakes used in general vehicles is fastened to the distributor pump bracket by two bolts, and the distributor pump bracket is then fastened to the swing bearing by two bolts.
To replace the brake shoes, we only need to remove the two bolts fastening the brake distributor pump.
Once the two bolts are loosened, we can remove the brake distributor pump.
Since the brake distributor pump has a soft hydraulic line, be careful not to pull too hard on it and just put it on the front axle suspension next to it.
Next, we need to polish the brake skins and chamfer the edges of the brake skins on the contact side of the brake discs.
In the maintenance operation of replacing the brake skins without replacing the brake discs, if you do not polish the brake skins, you will get brake noise.
This is because the old brake disc has a groove on it, which is the wear caused by the old brake skin on the disc; the old brake disc with the new flat brake skin will cause the noise because of the friction surface is too small.
When replacing both brake skins and discs, we do not need to grind the chamfer, we can just install them.
We need to apply some grease to the raised parts of the polished brake skins to reduce the rattling between the new brake skins and the distributor pump bracket.
Before installing the brake skin, we need to push the piston of the brake distributor pump inward so that the thicker new brake skin can be installed.
In order to avoid brake fluid spillage when pushing the piston inward, it is recommended to draw out some brake fluid in the brake fluid pot first, and then re-add the right amount of brake fluid according to the level of the pot after replacing the brake skin.
It should be noted here that different types of brake fluid cannot be mixed (such as DOT3 and DOT4), so it is better for the owner to add the corresponding brake fluid when adding.
Next, we first put the brake pads onto the distributor bracket, noting that the inner and outer brake pads are not interchangeable. Then, we can snap the brake distributor pump onto the distributor pump bracket
Finally, screw on the brake distributor pump bolts and tighten them with a torque wrench.
Generally speaking, the tightening torque of the brake distributor bolt is 20-30 Nm, please refer to the service manual of the relevant model for the specific parameters. Remember to tighten the wheel bolts after the wheels are installed.
The standard tightening torque of wheel bolts is 110-140 Nm, please refer to the maintenance manual of the relevant model.
The brake skin replacement for the rear wheels is very similar to the front wheels, so no details will be given here.
The whole process of replacing brake pads is not very complicated and the average person can learn it very quickly.
In the process of replacing brake pads, we need to pay more attention to safety as we have to lift the vehicle, even if a few bricks under the car can save your life in case of a critical situation.
I hope the above introduction can help you with your car and car maintenance.