Friday, March 13, 2009


This system can increase brake fluid pressure effectively with lighter pedal pushing force than that of conventional system,when emergency braking. On the braking of unskilled driver,even if pedal pushing speed of both skilled and unskilled drivers are same, unskilled driver cannot apply enough force on the brake pedal until the brake booster functions because the unskilled driver is rather hard to increase the pedal pushing force during braking comparing with that the skilled driver.

In the conventional type of brake booster system has an almost constant boost ratio from small to large pedal pushing force, but brake assist system makes the boost ratio larger when the pedal pushing force exeeds certain level.this is function of brake assist.

On conventional system the valve plunger , which transmits the operating force of operating rod to reaction disc, is one peace part. On brake assist system the valve plunger is divided into two pieces, and there is a rubber damper or a spring for boost ratio control between them.

Primary period
The power piston moves to left direction by booster function introducing atmospheric pressure,and the reaction disc starts to be deformed due to pressure from the power piston. By the pressure the deformed part of reaction disc goes into inside of a plunger plate holder.

Boost ratio increasing period
The deformed part of reaction disc inside of plunger plate holder contacts to plunger plate, and it compresses the control rubber damper of spring .By the compression a reaction force is applied on the reaction disc, and finally the reaction force is applied on output rod as an additional force from input rod.

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Monday, March 2, 2009



The force with which the driver steps on the brake pedal would not be enough to cause the brakes to operate to stop the vehicle quickly.
The brake booster therefore multiples the driver's pedal effort so that a large braking force is created.the brake booster may be an integrsl part of the master cylinder or fitted separately from it.
The brake booster has a diaphragm that is operated by the difference in pressure between atmospheric pressure and the vacum that is generated inside the engine's intake manifold.

The master is activated jointly by the pedal and the diaphragm to create a large braking force from a minimum of pedal effort.

Should the brake booster start to malfunction for one reason or another,it is designed in such a way that only the bossting power applied to the brakes is lost.The brakes will require additional pedal effort in such a case , but the vehicle can be braked normally without the booster.

On vehicle powered by a diesel engine , negative pressure is generated by a vacum pump because the intake manifold vacuum of a diesel is not sufficiently strong for this.The brake booster is installed between the brake pedal and the master cylinder,and consists of the following part;

  • Front/rear shell

  • Power piston ( diaphragm plate and valve body )

  • Input rod

  • Poppet seal

  • Output rod

  • Reaction disc

When the brake pedal is not depressed

The input rod,power piston and output rod are forced to the right by the diaphragm return spring.the air valve , consisting of the valve plunger and the interior of the poppet seal,closes, allowing no air to enter chamber B.Further, since the vacum seal, consisting of a power and exterior of the poppet seal, is open, chamber A is connected to chamber B through a vent hole provided in the power piston. both chambers contain a vacum due to the vacuum in the intake manifold.

When the brake pedal is depressed

When the brake pedal is depressed, the input rod and poppet seal move to the left( front), the vacum valve closes,and the vent hole connecting chambers A and B is blocked.Futher movement of input rod pushes the valve plunger and forces the air valve to open ,and air enters chambers B through a gap between the input rod and poppet seal.this causes a pressure differential between the two sides of power piston.The force resulting from this difference in pressure overcomes the force of the diaphragm return spring,moving the power piston to the letf ( front).The leftward movementof the power piston actuates the output rod,producing the required hydraulic pressure.

When the brake pedal is released

When the brake pedal is released, the master cylinder spring ,diaphragm return spring and pedal return spring cause the output rod,power pistonand input rod return to their original positions ( same as not depressed). The cause the air valve to close , and the vacum valve to open, so that the air in chamber B is drawn into the intake manifold, restoring the brake booster to its non-operating condition.

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Wednesday, February 25, 2009


The master cylinder converts the motion of the brake pedal into hydraulic pressure.

It consists of the reservoir tank, which contains the bake fluid ,as well as the piston and cylinder, which generate the hydraulic pressure.there are two types of master cylinder. The single master cylinder uses one piston to deliver hydraulic pressure to all four wheel cylinder.the tandem master cylinder uses two piston to deliver hydraulic pressure separately to the wheel cylinder of the front or rear wheels or the right front & left rear and the left front & right rear whells.The tandem type master cylinder is used more commonly than the single type.

The tandem master cylinder has two independent hydraulic lines , If either of the lines fails to function, the other line is still capable of functioning.
The separate systems for the front wheels and rear wheels are explained.
The primary and secondary pistons are installed inside the cylinder ,the secondary piston is supported by return springs in the front and back.The areas where the springs are act as pressure chambers with inlet port and return port for the brake fluid. The reserve tank connected to the inlet port is shared by both brake pipes for front and rear whells.

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Brake pad and shoe are basically made of the same materials.All genuine brake pad and brake shoe are manufactured from compound materials made from glass fiber,metalic fiber,carbon fiber, well as high quality filter ,binder, friction stabilizer and lubricant. these materials are carefully blended to provide superior characteristicand capability requaired for safe and adequate braking operation and power. advantages of genuine part listed below

  • The rotor will not suffer from excessive wear.
  • Braking power remains constant even at high temperatures.
  • Braking power varies little at different vehicle running speed.
  • Abrasion remains constant at varying temperatures.
  • Braking power remains constant even when brakes at wet.
  • Squeling noise rarely occur.

Inferior quality non-genuine part may result in;

  • Faster wearing and more frequent replacement,hence high maintenance cost eventually.
  • Uneven braking.
  • Unsafe brake fade.
  • Abrasion to disc or drum.

For safety riding replace the brake pad or brake shoe after the thickness is close to the minimum limit , the limit you know by asked to your dealer. if minimum limit is to used it is very dangerous situation before next periodic maintenance.In that case , It not only takes time and inconvenience for you, but may cost more when completelt worn out pads have damaged rotors.So inspect and correct or replace as necessary the brake pad every 20.000 km.The back side of the pad has a metal clip. when the pad wears to minimum limit , this metal clip rubs against the dasc and makes a scratching noise which serves as a warning. the friction of pad and rotor or brake shoe and brake drum becomes worn it. and if the rotor or drum wears out;

  • Braking performance become poor.
  • Vibration will happen ( pedal vibration or judder)
  • Steering vibration will happen when braking

If the condition happen, measure the thickness as instructed in service manual. Grind when it can be done within specified limit, if not replace with new one.

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Saturday, February 14, 2009


The brake as function is to stop vehicle or to decelerate of speed of vehicle and to be parked on a slope, as well brake it extremely importent part in vehicle so it is safety component and very vitally. Brake are expected to be highly realible, as well as durable so that the vehicle can be stopped both safely and promptly in any place and under any conditions.
The part of brake system;

  • Brake fluid
  • Brake shoe and Brake pad
  • Brake rotor and Brake drum
  • Brake pedal ( foot brake/parking brakea)
  • Brake pipe line
  • Brake master

Function of part;

  1. Brake fluid transfer the power to the brake pads and brake shoes via brake line to stop the cars or to reduce of speed ,as well brake fluid necessary maintenance to keep of quality. brake fluid will deteriorate by moist in air mixing with fluid through brake pipe or reservoir tank also deteroited by oxidation due to the friction heat,if brake fluid deteroites it may cause the corrotion inside the cylinder and if brake fluid contains moist ,the boiling point become lower. As brake fluid is used under severe conditions, vapor lock may easily as aresult of brake fluid boiling. So the brake fluid must be inspect and correct or replace as necessary and maintenance fluid level and leaks. Replacement of brake fluid is recomended every 40,000 km or two years or if brake fluid become very dirty under high humidity.
  2. Brake pad or brake shoe produce a braking force ,brake pad is used in disc brake system . In disc brake system,a disc rotates with the whell,and brake pads clamps this rotating disc to produce a braking force.In brake shoe in used in drum brake system . In a drum brake system brake shoe expand outwards to press the linings against the drum inner surface which is rotating, to produce the braking force.brake pad or brake shoe become worn by friction .if brake pad or shoe worn is continuosly used;
  • Original brake performance can no longer be guaranteed.
  • Pad wear indicator will make squeling noise,if completely worn out,brake function will almost be loss,leading to very dangerous situation for passengar.
  • Worn pad/shoe will cause damage to the brake discs or drums.

Pad wear indicator : When pad thickness approaches the specified limit,small nails riveted to the pad will scratch the rotor surface when the brake are applied, making squealing noise which warns the driver that pads should be replaced.

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