Brake roller testing and adjusting push rod

Brake roller testing was done at the Mt Albert campus. We worked on a Mitsubishi lancer and the brakes stayed with in 30% for all four wheels and that's good enough to pass.

Adjusting push rod
The length of the push rod can be adjusted to reduce the clearance between the piston and the push rod. To find out how much the push rod had to be adjusted we measured the length of it from the surface of the booster to the end of the rod. We measured the inside of the master cylinder from the outside edge to the piston and subtracted the distance from the surface that gets bolted to the booster to the outside edge that goes into the booster. We then took the measurement of the length inside the cylinder and subtracted the length of the rod to fined the clearance and how much adjustment the push rod needed. If the clearance is correct the brakes will be more responsive and it could reduce a vehicles stopping distance. 

Brake Booster

http://www.youtube.com/watch?v=Nk6e5tTVsm8

This video explains everything :) ^^^

If the pedal feels "hard" while the engine is running, the booster isn't operating correctly. If you suspect the booster is defective, do not attempt to disassemble or repair the power booster. Doing so is unsafe and will void your warranty.

Test 1

1. With the engine off, pump the brake pedal to remove any residual vacuum in the booster.
2. Hold pressure on the pedal while you start the engine. When the engine starts, the pedal should drop about a 1/4", this indicates that the booster is working properly.

Test 2

1. Run the engine a couple of minutes.
2. Turn the engine off and press the pedal several times slowly. The first pump should be fairly low. The second and third should become slightly firmer. This indicates an airtight booster.

Test 3

1. Start the engine and press the brake pedal, then stop the engine with the pedal still pressed. If the pedal does not drop after holding the pressure on the pedal for 30 seconds, the booster is airtight.

Inspect the Check Valve

1. Disconnect the vacuum hose where it connects to the intake manifold. Do not disconnect the vacuum line from the booster. Air should not flow when pressure is applied, but should flow when suction is applied. If air flows in both directions or there is no air flow, the valve needs to be replaced.

Verify Enough Vacuum

1. Check the operating vacuum pressure when the engine is at normal operating temperature. There should be a minimum of 18 in. of vacuum. Vacuum may be increased by properly tuning the engine, checking for vacuum leaks and blockages in vacuum lines.

When we step on the brake pedal, the booster's diaphragm squeezes the air in the front side of the booster. This pressure unseats the check valve that controls intake manifold vacuum. When the check valve opens, manifold vacuum sucks the air out of the booster. This "suction" called negative pressure, pulls the diaphragm forward, which applies forward pressure on the rod and master cylinder piston. The power booster helps us apply the brakes.

Flaring Brake pipes

Basically, this is the way to flare a brake line: Begin by using a tubing clamp to cut the line to the length you need. Then, before you make the flare, place the brake line fitting (which will eventually connect the line to other parts of the braking system) over the tube. Place the tubing in a clamp to hold it steady. Next, take the flaring tool and insert it into the end of the tube you want flared. The flaring tool looks a little bit like a pitchfork with three prongs. Two prongs attach to the clamp holding the brake line, and the third prong (the one in the middle) actually flares the line. It's mobile; you screw it in and out of the line, which widens it, making the flare.

REF: http://auto.howstuffworks.com/auto-parts/brakes/brake-parts/brake-lines2.htm

      Double and single flare

Master cylinder

FREE PLAY

And this is where the foot pedal's "free play" comes from. It is absolutely necessary that there be some amount of clearance, otherwise the seals may be pushed forwards enough to prevent the intake/return ports from ever opening up again to allow excess pressure to vent to the reservoir.

The factory manual for my car specifies 1mm to 5mm clearance.

What fluid to use?
 Always use the same as recommended of one D.O.T over, just never go below.

Function of master cylinder
A master cylinder is an automotive device that applies hydraulic pressure to the braking system. The master cylinder is typically located in the engine compartment and is fitted with a removable cap to add brake fluid.

Applies Pressure to Brakes

·         A brake master cylinder converts pressure from the brake pedal into hydraulic power that causes the brakes on an automobile to operate. The master cylinder works in a similar manner to a syringe; as pressure is applied, the brake fluid is pushed out of the cylinder toward the brakes.

Brake Safety

·         Most brake master cylinders have two chambers that each operate a set of wheels. Master cylinders are designed in this way in case of a failure in the brake system from a broken brake line or other problem. If the brakes serving one set of wheels fail, the other set will still have powered brakes.

Stores Excess Fluid

·         A reservoir is built into master cylinders to hold excess brake fluid. When the brakes are applied the fluid is forced into the brake line, causing the brakes to operate. When the brake pedal is released the fluid is allowed to escape back into the reservoir, releasing the brake system.

Brake Calipers

There are floating and fixed callipers. The floating piston consist of one piston and the fixed calliper only has two pistons. 

Brake callipers hold the brake pads and force them against the brake rotors when you push on the brake pedal. The callipers move in and out on slide pins, which must remain free of corrosion, excessive brake dust and road dirt. Dirty or not lubricated calliper slide pins are the biggest cause of sticking brake callipers. When performing brake pad replacement, always make sure you take care of the calliper slide pins in order to avoid a sticking brake calliper.

The disc brake calliper assembly is bolted to the vehicle axle housing or suspension.

There are 2 main types:

FIXED AND SLIDING

Fixed callipers can have 2, 3, or 4 pistons. 2-piston callipers have one piston on each side of the disc. Each piston has its own disc pad.

When the brakes are applied, hydraulic pressure forces both pistons inwards, causing the pads to come in contact with the rotating disc.

The sliding or floating calliper has 2 pads but only 1 piston. The calliper is mounted on pins or bushes that let it move from side to side.

When the brakes are applied, hydraulic pressure forces the piston inwards. This pushes the pad against the disc. The calliper is free to move on slides, so there is a clamping effect between the inner and outer pads. Equal force is then applied to both pads which clamp against the disc.