Practical Automotive Maintenance: Brake System Overview
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Brake System Overview
05.12
| 00:00 | In this section of the course we're going to cover everything we need to know about servicing the braking system in our car. |
| 00:06 | Regular maintenance and inspection of each component is crucial to ensure optimal performance as worn brake components can significantly reduce braking efficiency and compromise safety. |
| 00:17 | First let's take a high level look at the braking system before diving into each major component in more detail. |
| 00:23 | Most of this should be very obvious, but there are a few more subtle details that make it worth covering the basics. |
| 00:30 | The primary function of a braking system is of course to provide the driver the ability to slow or stop the vehicle as needed. |
| 00:37 | When a car is moving it possesses kinetic energy which is dependent on the speed it's moving and its mass. |
| 00:43 | Energy can't just disappear though. |
| 00:45 | In order to slow the car down the kinetic energy needs to be converted into another form of energy, in this case heat. |
| 00:52 | This is achieved through the friction between the brake pad and the rotor or the brake shoe and the drum when clamping pressure is applied. |
| 01:00 | Depending on the amount of energy we need to disperse this can generate a lot of heat and managing this heat is one of the biggest challenges with a performance brake system. |
| 01:09 | Let's take a step back however and start at the start which is with the brake pedal. |
| 01:13 | This of course is our control input for the brake system and the force we apply to the brake pedal is used to generate hydraulic pressure in the brake master cylinder. |
| 01:22 | Generating the required pressure to stop the car would be impossible if the pedal was connected directly to the master cylinder, so two tricks are used to make this manageable. |
| 01:31 | Firstly, the brake pedal takes advantage of a leverage ratio to multiply the driver's effort. |
| 01:37 | For example, the pedal may have a six to one ratio meaning that the driver's pedal effort is multiplied by a factor of six. |
| 01:44 | There's no free lunch however as this also means that the pedal needs to move further to achieve the required pressure. |
| 01:50 | This is not an issue however as it is part of the brake system design. |
| 01:54 | The other component that makes this manageable is the brake booster. |
| 01:57 | This is a device that's located between the pedal and the master cylinder. |
| 02:01 | We don't need to get into the inner workings of the brake booster, but essentially it uses engine vacuum to help multiply the force exerted by the driver. |
| 02:09 | Next we have the actual brake master cylinder or cylinders. |
| 02:13 | In race cars we'll often use separate cylinders for the front and rear brake circuits and these will be fitted to a pedal box that eliminates the brake booster that we just discussed. |
| 02:23 | This is a niche case that's not relevant to road cars, so we will leave it at that. |
| 02:27 | Road cars on the other hand will most likely incorporate the two master cylinders into a single inline cylinder that bolts to the brake booster. |
| 02:35 | The reason we need a separate master cylinder for the front and rear brake circuits is because the front brakes do the majority of the work as much as 60 to 70 percent. |
| 02:45 | This is due to the weight transfer under hard braking. |
| 02:48 | Essentially the load applied to the front tires increases meaning that they have more available grip and can do more of the stopping. |
| 02:55 | Conversely there is less load on the rear tires, so we need to apply less brake force to these wheels or we risk locking up the wheels. |
| 03:03 | The brake master cylinder uses a piston that moves in a cylindrical bore. |
| 03:07 | When force is applied to the piston by the brake pedal it works against the brake fluid to generate pressure. |
| 03:12 | This hydraulic pressure is then transferred to the respective corner of the car via the brake lines. |
| 03:18 | Modern braking systems and particularly those on performance cars will almost always use disc brakes. |
| 03:23 | This consists of a brake disc or rotor on each corner of the car along with a brake caliper that contains the brake pads. |
| 03:30 | On the other hand, older vehicles and low spec commuter vehicles often use drum brakes or a combination of disc brakes on the front and drums on the rear. |
| 03:38 | This combination is used because the front brakes do the majority of the work as we just learned. |
| 03:43 | A drum brake consists of a large diameter cast iron drum that slips over the wheel studs. |
| 03:49 | Inside are a set of brake pads although in this case they're referred to as brake shoes. |
| 03:54 | Unlike a brake pad for a disc brake, brake shoes have a curved surface to match the internal diameter of the brake drum. |
| 04:00 | Besides sometimes being integrated into a rear modern disc brake system as a separate handbrake, which we'll look at soon, drum brakes aren't well suited to performance applications due to the weight of the system and the inability to easily disperse the heat they create. |
| 04:15 | Keep in mind that the purpose of this section is maintenance specific, so we don't need to have an F1 level of knowledge about the design and installation of a brake system in order to bleed your brakes or change the pads. |
| 04:27 | On the other hand, we believe that properly understanding a system can be beneficial, particularly when it comes to diagnosing faults. |
| 04:35 | If you get to the end of this section and you want to dive much deeper into the performance of motorsport braking systems, I highly recommend checking out our brake system design and optimization course. |
| 04:45 | Let's quickly summarize before we dive into brake systems in detail. |
| 04:49 | This section of the course focuses on the fundamentals of identifying and servicing a vehicle's braking system, focusing on the basic knowledge and maintenance procedures. |
| 04:58 | In simple terms, hydraulic pressure created by the driver pressing the brake pedal forces brake pads onto the brake rotors to convert kinetic energy into heat in order to slow the vehicle. |
