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Disc Brakes

Last Update:

09/06/2016

Introduction

Brakes are all about bringing moving vehicles to a stop. Brakes evolved as automobiles evolved in order to deliver better braking power.

The Disc Brake stands out for its superior braking characteristics and lack of brake fade, a phenomenon common in drum brakes. Most modern cars today have disc brakes sitting at the front and rear, providing incredible stopping power.

History:

  • Disc brake may have been first invented by William Lanchester and patented it in 1902. Although even before Lanchester, Elmer Ambrose Sperry is said to have designed and electric car with front wheel disc brakes way back in 1898.
  • The first design was a rudimentary disc made of copper and the pads were pushed by a cable. These brakes remained dormant for long though as drum brakes advanced.
  • The Crosley was perhaps the first car to acquire disc brakes in 1949.
  • At around the same time Chrysler fitted a disc brake on their Imperial car but it was not the true disc brake, since it was the discs that rubbed inside against a drum instead of the usual caliper-wheel arrangement.
  • Austin-Healey 100s model sported disc brakes in 1955 followed by Jensen who fitted disc brakes to all four wheels in their 541 Deluxe model in 1956. Triumph fitted these brakes to their TR2 model in 1955 followed by the TR3 in 1956 sporting Girling front disc assemblies.
  • Jaguar was another manufacturer to adopt disc brakes around the same time as Austin Healey
  • But it was the Citroen DS, a mass produced car that can be said to have truly brought disc brakes to mainstream.

Still, the systems were primitive and it was not until 1964 when the Studebaker Avanti rolled out with disc brakes that made the auto industry take a serious interest in this system. European made cars had disc brakes back in the 1950s but it took another 20 years for American cars to switch to this system.

Evolution and improvement

  • The earliest disc brake by Lanchester had a thin copper disc that wore out quickly. Besides, the calipers were activated by a lever through a pedal. Today, the disc brake evolved into a standard type consisting of a cast steel rotor fitted to the hub with a static caliper and brake pads on either side of the rotor.
  • The opposed piston type disc brakes incorporate pistons on either side of the rotor wheel. Pressure is distributed evenly between the two pads.
  • Most simple units have 2 pistons while more advanced ones may have 4 or 6 to increase braking power.
  • In contrast, the floating caliper type brake incorporates a piston only on the inner side, pushing the pad against the rotor. The caliper too moves along a pin. This design is mostly used in cars.

There are further refinements in disc brakes mainly relating to the rotor. A rotor may have a plain surface, a drilled surface, a grooved surface or a dimpled surface, or a combination of any of these to enable better braking and heat dissipation. The purpose is to provide better grip for the pads, allow gases and debris to escape and reduce weight.

Main parts

The main parts of a Disc Brake are:

  • A rotor fitted to the hub of the wheel
  • A stationary caliper sitting on top and surrounding a part of the rotor and bolted to the suspension.
  • The caliper incorporates piston that push brake pads against the rotor when actuated.
  • A master hydraulic cylinder-piston assembly connected to the brake pedal (or brake lever on Two Wheelers). Power assisted brakes may have a DC motor pump to generate high pressure.

 

How It Works

  • Pushing the brake pedal actuates the piston inside the hydraulic master cylinder, either directly or through a brake boosting system.
  • The master cylinder generates hydraulic pressure transmitted through a hydraulic hose to the pistons at the caliper.
  • The pistons are held in place by rubber seals that seal the unit and also provide the spring action to move pistons back in place.
  • When the pistons are pushed they operate the friction pads that clamp down on the rotor and bring the vehicle to a stop. 
  • Once hydraulic pressure is removed the seals in the caliper allow pistons to retract.

Effectiveness and Challenges

  • Disc brakes are superior to drum brakes in that they are not prone to “fade”. Because they are exposed to air and the heat is dissipated quickly. This comes in handy where hard stop and starts are frequent or when riding down an incline.
  • Water and dust as well as debris are ejected by the spinning rotor so there is no build of water that can reduce braking power. Disc brakes are not much affected by wet weather.
  • Disc brakes have higher braking power and can quickly bring a speeding vehicle to a halt at a short distance, especially when fitted to both the front and rear wheels.

The challenges are that disc braking systems require higher hydraulic pressure and are expensive in comparison to drum brakes.

  • Also, the pads are small and clamp down on only a part of the circumference of the rotor. Effectiveness could be raised if a system could be devised with larger pads to provide greater clamping area.
  • The piston in the caliper can jam due to wear and tear of the rubber retainer and this might result in the brakes being applied unintentionally.
  • Cast iron rotors wear down and need replacement. Ceramic and use of reinforced carbon discs in advanced as well as racing cars have mitigated this but again, these are expensive.
  • Pads can wear out quickly and must be replaced with exactly the same type to avoid issues.

 

Maintenance Tips

  • For Disc Brake to be effective the hydraulic system needs to be in perfect condition. Maintain master cylinder and check hose for cracks, leaks and ruptures regularly specially in hot and humid environment.
  • Check piston caliper and retaining rubber to make sure the rubber is not cracked or hardened due to exposure to weather. Replace if necessary.
  • Check brake pads and replace as recommended.

Disc brakes are now standard on front and rear wheels of most modern cars and motorcycles, pointing to their superior characteristics and agility it provides.  

 

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