In this last part we share some disc brake maintenance tips, its working along with the various advantages and disadvantages over drums…
In the first three parts of this disc brake series, we have seen the different components of the Disk brake assembly like brake disc/rotor, caliper assembly and master cylinder assembly. If you have missed reading them, we are pasting their links here…
- Types of Disk Brakes – Advantages & Disadvantages (Part 1)
- Disc Brake Calipers – Parts, Types, Advantages & Disadvantages (Part 2)
- Disk Brake Master Cylinder Assembly, Types, Pros & Cons (Part 3)
But what is the principle behind disk brakes and how does it work? Let’s have a look.
Disc Brake – Working
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
In the above picture Area 1 has a very small surface and Area 2 has a larger surface. Now when you apply force to Area 1 the fluid below it travels to Area 2. As the Area 2 has larger surface, the force to Area 1 multiplies and lifts the car.
The law simply suggests that when pressure is applied to any point in static fluid in a container then there is an equal increase in pressure at every point in the 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 the lever or pedal and master cylinder piston pushes it (the master cylinder piston). This movement allows the master cylinder piston to slide and push the return spring inside the bore of the master cylinder, which generates pressure in the 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 to the other side.
Then the fluid enters in to the cylinder bore of caliper assembly via brake hosepipes and pushes the caliper piston. 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 to the brake disc which creates friction and stops the brake disc/rotor from rotation. This way the 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 the cylinder bore of caliper till both caliper piston and piston ring come to 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 to its original position and allows the fluid to flow back to the reservoir via hosepipe and master cylinder bore.
Disc Brake Advantages
- Disk brake requires less effort (brake torque) to stop the vehicle compared to drum brakes.
- It generates less heat compared to drum brakes for the same brake torque.
- Ease of maintenance as disk brake is outside the wheel rim.
- It cools down faster.
- In drum brakes, if worn out brake shoes are not changed at proper time they can damage the drums however, disk brakes do not have such problems.
- It is less likely to skid compare to drum brakes in wet condition (when applied with caution).
- It is safer than drum brakes under hard braking conditions.
- It has brake pad wear indicator which is not present in drum brakes.
Disc Brake Disadvantages
- It is expensive.
- More skills required to operate disk brakes. That is the reason why some people are still not comfortable with disk brakes.
- If any air remains in disk brake system, it can be problematic as brakes may not work effectively.
- Disk brake assembly has more moving parts and it is more complex than drum brakes.
- It requires lot of efforts in maintenance like brake fluid (bleeding), change of brake pads etc.
Disc Brake Maintenance Tips
Brake is a life saving equipment in your vehicle. You must maintain your vehicle’s braking system in good condition to avoid brake failures. Following are some maintenance tips for disk brakes.
- Check your brake disc/rotor for any kind of dirt or contamination of oil. If it is found take a plane cloth and clean the surface then you can use Isopropyl alcohol (IPA) with thick cloth (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 you have is to replace the brake disc/rotor.
- Check the caliper mounting like bushes and pins/bolts. Clean and lubricate the pins 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 the caliper from the bike. For this you will need to remove the caliper mounting pins/bolts. Once you remove the pins/bolts the caliper is free you can slide it from the brake disc. Do not remove the caliper when it is hot or if the wheel is spinning.
- After removing the caliper check the brake pads thickness. As brake pads wear out 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 them.
- Check brake pads if there is any kind of dirt, mud particles or contamination of oil. If present first clean with plane cloth and then clean it with Isopropyl alcohol.
- While replacing brake pads make sure you put the inner and outer pads at the right place. Generally it is written on the back side of brake pads which one is inner and which one is the outer pad. You should also make sure that the difference between the brake pads and brake rotor remain equal on both the side. Also, ensure all the parts are present like anti rattle spring, etc.
- New brake pads always require some bedding. To bed the brake pads ride your vehicle at 40-50 Kph and apply brakes to stop it. Do it for 20-25 times. Allow brake pads to cool after each braking. Your brake pads are now ready.
- Check caliper piston for any kind of dirt or contamination of oil, if it is present 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.
- Always use sealed container brake fluid with specified grade like DOT3, DOT4. Do not open the container till you are prepared to change the 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 you find any irregularities change that part. 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 trained mechanics. If you are unsure of anything simply don’t break it!
Disc Brake noise & squeal:
Brake squeal occurs due to vibrations between the brake disk/rotor and brake pads or brake pads and caliper.
Apart from the 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 a 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 of brake squeal.
This is the end of our braking series. Hope you like it. Share it with your friends if you find it informative… 🙂
– Mahavir Kothari