Till now we have seen parts of Disk brake Assembly like brake disc/rotor, caliper assembly and master cylinder assembly. But what is the principle behind disk brake and how it works? Let’s have a look.
A disk brake works on the principle of Pascal’s Law/Principle of transmission of fluid pressure. Pascal’s law developed by French mathematician Blaise Pascal states that “pressure exerted anywhere in a confined incompressible fluid is transmitted equally in all directions throughout the fluid such that the pressure ratio (initial difference) remains same.”
In the above picture Area 1 has very small surface and Area 2 has very large surface. Now when you apply force to Area 1 the fluid below it travel to Area 2 which has larger surface area. As the Area 2 has larger surface, the force apply to Area 1 multiplies and lifts the car.
The law simply suggests that when a pressure is applied to any point in static fluid in a container then there is an equal increase in pressure at every point in container. Another example is when you press a hydraulic jack pressure given at one point creates the same pressure at other point and hence you can lift more weight by just applying slightest force on the jack.
Now let’s see how this principal works in case of disk brake.
When a brake lever or pedal is pressed, the push rod which is connected to lever or pedal and master cylinder piston pushes the master cylinder piston. This movement allows the master cylinder piston to slide and push the return spring inside the bore of master cylinder, which generates pressure in reservoir tank. At this moment a primary seal allows the brake fluid of reservoir tank to flow over it into the brake hosepipes. A secondary seal ensures that the brake fluid does not go other side.
Then the fluid enters in to cylinder bore of caliper assembly via brake hosepipes and pushes the caliper piston or pistons. At this time the piston ring moves in rolling shape with piston. Then the caliper piston pushes brake pad. This movement causes brake pads to stick with brake disc which creates friction and stops the brake disc/rotor to rotate. This way disk brake system stops or slows down the vehicle.
When the brake lever or pedal is released the piston ring pushes the caliper piston back to cylinder bore of caliper till both, caliper piston and piston ring come into their original shape. At this time retraction spring pushes the brake pads to their original position. The return spring in master cylinder assembly pushes the master cylinder piston back into its original position and allows the fluid to flow back to reservoir via hosepipe and master cylinder bore.
Advantages of Disk Brake:
- Disk brake requires less effort (brake torque) to stop the vehicle compare to drum brake.
- It generates less heat compare to drum brake for the same brake torque.
- Ease of maintenance as disk brake is outside the wheel rim.
- It cools down faster compare to drum brake.
- If worn out brake shoes are not changed at proper time it can cut the brake drum in drum brake. Disk brake does not have such problem.
- It is less likely to skid compare to drum brake in wet condition.
- It is much safer than drum brake in hard braking condition. Under such condition drum brake can lock up the rear wheel.
- It has brake pad wear indicator which is not there in drum brake.
Disadvantages of Disk Brake:
- It is expensive compare to drum brake.
- More skills require to operate disk brake compare to drum brake that’s the reason why some people are not comfortable with disk brake
- If any air remains in disk brake system, it can cause accident as the brake will not work effectively.
- Disk brake assembly has more moving parts and much complex than drum brake.
- It requires lot of effort at maintenance front like brake fluid (bleeding), change of brake pads etc compare to drum brake.
Brake is a life saving equipment in your vehicle. You must maintain your vehicle’s brake system in good condition to avoid brake failure situation. Following are the maintenance tips for the disk brake system.
- Check your brake disc/rotor for any kind of dirt or contamination of oil, if it is found take a plane clothe and clean the surfaces than use Isopropyl alcohol (IPA) with thick clothe (in order to avoid direct touch to IPA) to clean oil contamination on the rotor (Be careful IPA is highly flammable and dangerous for health).
- Check your brake disk/rotor for any kind of scar, warp or crack. In case of scaring or warping you can resurface the brake disc/rotor if the thickness of the rotor allows you to do it. The thickness of brake/disc rotor should not be less than prescribed standards (generally in manuals) after resurfacing. In case of cracking the only option left is to replace the brake disc/rotor
- Check the caliper mounting like bushes and pins/bolts. Clean and lubricate the pin and bushes and adjust as required. Change bushes and pins/bolts if required.
- Check the caliper mounting bracket (Adapter) for any kind of wear and clean it. If it is badly worn or rusted change it. Same way check the caliper body.
- To check entire caliper assembly you need to remove caliper from bike. For this you need to remove caliper mounting pins/bolts. Once you remove the pins/bolt the caliper is free you can slide it from brake disc. (Do not remove caliper when it is hot or wheel is spinning)
- After removing the caliper check the brake pads thickness. As brake pad is wear and tear part of caliper assembly it needs to be inspected regularly. Most of the caliper assembly and brake pads come with wear indicator. If the pads are worn out or thickness of the pads is less than 1/8 inches, replace it.
- Check brake pads if there is any kind of dirt, mud particles or contamination of oil. If it is there first clean with plane clothe and then clean it with Isopropyl alcohol.
- While replacing brake pads make sure you put inner and outer pads at right place. Generally it is written on the back side of brake pads which one is inner and which is outer pads. You should also make sure that the difference between the brake pads and brake rotor remain equal both the side. Also, ensure all the parts are there like anti rattle spring.
- New brake pads always require some bedding. To bed the brake pads ride your vehicle at 40-50 KMPH and apply brake to stop vehicle. Do it for 20-25 times. Allow brake pads to cool after each brake. Your brake pads are now ready.
- Check caliper piston for any kind of dirt or contamination of oil, if it is there clean with Isopropyl alcohol. If the piston is out of shape change it.
- It is advisable to change caliper piston rings and dust boot when you change caliper piston.
- Check hosepipe for any leak, crack or wear. This situation allows air to enter into the brake system. If there is any leak or crack change the hosepipe.
- Check your master cylinder assembly for any kind of scratches. Check reservoir tank for any kind of leak. If scratch or leak found change the part.
- Check your brake fluid level and color of brake fluid. If brake fluid is at low level or brake fluid is deteriorated (dark color) change it. The brake fluid change process is called brake bleeding process
- Always use sealed container brake fluid with specified grade like DOT3, DOT4. Do not open the container till you are prepared to change brake fluid.
- If you want to service master cylinder assembly do it just before the bleeding process. Remove the lever, and then take out the push rod, piston, primary cup and secondary cup. Ensure there is no cut in primary or secondary cup. If it is there change it. Clean master cylinder piston with Isopropyl alcohol and then fit it in the same manner.
Note: (The information is for awareness only. Please don’t open entire caliper assembly or master cylinder assembly without any prior experience. You can do the bleeding process and outside cleaning job and that too with utmost care. Leave the other things to professional mechanic. If you are unsure for anything don’t do anything.)
Brake noise and brake squeal:
Brake squeal occurs due to vibrations between the brake disk/rotor and brake pads or brake pads and caliper. Brake noise occurs due to reason other than mentioned in brake squeal.
Apart from above mentioned maintenance tips brake squeal can be reduced by installing insulator shims on the back of brake pads. It provides cushion to brake pads and reduce vibrations. You can also apply moly-based dry lubricant on the back of pads or apply a noise suppressing compound on the back of pads to reduce vibrations. If the manufacturer has provided semi-metallic pads then it can also be reason of brake noise. You can use non-metallic ceramic pads or Non-asbestos organic pads to reduce noise. Sometimes the design of pads is also a reason for brake squeal.
We are ending brake series here, hope you like all the articles.
(Note: It is difficult to cover everything in just one article like bleeding process and other things will write some day on that.)
- Mahavir Kothari