STEERING SYSTEMS-- Steering Rack

Steering Rack

Steering racks are a component in rack-and-pinion steering controls. They are the metal part on which gears, or pinions, slide back and forth, determining how far a corresponding wheel turns.



steering rack



Disassemble & Reassemble

 

special service tools:

1.adjuster nut spanner

2.gland nut spanner

3.tube nut spanner

4.DTI(dial test indicater)

5.V blocks

pinion and rack

tie rod end & tie rod

rack body & pinion assembly



pinion housing



pinion housing





pinion
count the number of teeth on the pinion :8







rack

count the number of teech on the rack:27



the magnetic base of the DTI requires a metal bench to work correctly.
rack run-out reading:0.05mm

PS: casting for rack mount broken!

ABS

An anti-lock braking system (ABS) is an automobile safety system that allows the wheels on a motor vehicle to continue interacting tractively with the road surface as directed by driver steering inputs while braking, preventing the wheels from locking up (that is, ceasing rotation) and therefore avoiding skidding. It is an automated system that uses the principles of threshold braking and cadence braking, that was practised by skilful drivers with previous generation non-ABS braking systems.

Vehicles with ABS are equipped with a pedal-actuated, dual-brake system. The basic hydraulic braking system consists of the following:

•ABS hydraulic control valves and electronic control unit
•Brake master cylinder
•Necessary brake tubes and hoses
The anti-lock brake system consists of the following components:
•Hydraulic Control Unit (HCU).
•Anti-lock brake control module.
•Front anti-lock brake sensors / rear anti-lock brake sensors.


Braking force and the tendency of the wheels to lock up are affected by a combination of factors such as the friction coefficient of the road surface, and the difference between the vehicle speed and the road wheel speed. The ABS prevents the road wheels from locking up during heavy braking by controlling the vehicle's brake system hydraulic pressure.
During normal braking, as the rotational speed of the wheel falls, no electric current flows from the ECU to the hydraulic unit. The solenoid valve is not energized. The brake master cylinder hydraulic pressure is applied to the brake unit, and the ABS is not involved. However, even though the ABS is passive during normal braking, its control module is constantly monitoring for rapid deceleration of any of the wheels.
If a wheel-speed sensor signals severe wheel deceleration - which means the wheel is likely to lock up - the ECU sends a current to the hydraulic unit. This energizes the solenoid valve. The action of the valve isolates the brake circuit from the master cylinder. This stops the braking pressure at that wheel from rising, and keeps it constant.
If the sensors signal the wheel is still decelerating too rapidly, the ECU sends a larger current to the hydraulic unit. The armature moves even further and opens the valve. It opens a passage from the brake circuit. Brake fluid is sent from the brake circuit back to the master cylinder. Pressure in the brake caliper circuit is reduced so that the wheel is braked less heavily.
If the wheel sensors indicate that lowering the brake pressure is letting the wheel accelerate again, the ECU stops sending current to the hydraulic unit and de-energizes the solenoid valve. This lets the pressure increase, so that the wheel is again decelerated.
This cycle repeats itself about four to six times per second.
It is normal in an ABS for the valves in the hydraulic control unit to keep changing position as they change the brake pressure that’s being applied. These changes in position may cause rapid pulsations to be felt through the brake pedal.

Brake roller testing

Some of the main systems that are tested include:

­ Brakes and ABS
­ Transmission
­ Parking PAWL and Parking Brake
­ Speed Control
­ Traction Control and Electronic Stability Programs (ESP)
 Vibration Analysis
­ Speedometer Accuracy
­ Body / Chassis / Electrical Controllers
­ Vehicle Electronic Control Unit (ECU)
­ Tire Pressure

repair the master cylinder

when the master cylinder fails,the master cylinder may be the seals around the pistons.the pisten should be removed and the cylinder need to check for corrosion, cause brake fluid deaws in water and if the vehicle is parked for too big ,it can cause the master cylindto corrode.








If it is a steel cylinder it can be honed using methalated spirits or kerosene with a honing tool and then it should be cleaned out with brake cleaner.







Master Cylinder & Brake calliper

Master Cylinder:

the master cylinder is a control device that converts non-hydraulic pressure into hydraulic pressure. This device controls slave cylinders located at the other end of the hydraulic system.
As piston move along the bore of the master cylinder, this movement is transferred through the hydraulic fluid, to result in a movement of the slave cylinder. The hydraulic pressure created by moving a piston toward the slave cylinder compresses the fluid evenly, but by varying the comparative surface-area of the master cylinder and/or each slave cylinder, one can vary the amount of force and displacement applied to each slave cylinder, relative to the amount of force and displacement applied to the master cylinder.
The most common vehicle uses of master cylinders are in brake and clutch systems. In brake systems, the operated devices are cylinders inside of brake calipers and/or drum brakes; these cylinders may be called wheel cylinders or slave cylinders, and they push the brake pads towards a surface that rotates with the wheel until the stationary brake pad create friction against that rotating surface.



Brake Caliper:

A brake caliper is a device used to push the brake pads against the surface of the brake rotor to slow the car down.

The brake caliper works with hydraulic pressure, every time you push the brake pedal, the brake fluid travels from the brake master cylinder to the brake proportioning valve ( when the car is not equipped with ABS ), if the car has ABS, the brake fluid travels through the ABS Hydraulic control unit, and from there the brake fluid travels inside the brake lines all the way to the brake calipers, this hydraulic pressure pushes one or more cylinders inside the brake caliper against the brake pads, this pressure forces the brake pads to make contact with the brake rotor, the force will ve relatively equal to the force applied by the driver to the brake pedal.

- The bad brake caliper are the following:
1- Brake fluid is leaking past the seals in the caliper pistons.
2- The car always pulls to one side when the brakes are applied ( signs of a sticking brake caliper )
3- Premature brake pads wear. ( Also caused by sticking brake calipers )

Brake fluid

1. Low viscosity

2. Compatibility with rubber, other brake fluid BUT not synthetic

3. Lubricating properties

4. Resistance chemical ageing 

5. Higher boiling point

6. Water absolution

                           DOT 

            3              4              5

dry      205c        230c        260c

 

wet      140c       155c        180c

Brake System( disc, dyum,bleeding...)

Composition

The brake system consists of the control system, hydraulic system and power system.
1.Control system: pedal, handbrake                                                          
2.Hydraulic system: brake pump, hydraulic tubing                                            
3.Electronic control system: ABS pump, ABS sensor, ABS computer                             
4.Execution System: brake calipers, brake pads, brake discs

Type: Disc brake & Drum brake

drum brake:

Drum brakes, use a wide cylinder that is open at the back, similar in appearance to, well, a drum. When the driver steps on the brake pedal, curved shoes located inside the drum are pushed outwards, rubbing against the inside of the drum and slowing the wheel.

dice brake:
Disc brakes,use a flat, disk-shaped metal rotor that spins with the wheel. When the brakes are applied, a caliper squeezes the brake pads against the disc, slowing the wheel.

What is the difference between disc brakes and drum brakes?

Disc brakes are generally considered superior to drum brakes for several reasons. First, they dissipate heat better (brakes work by converting motion energy to heat energy). Under severe usage, such as repeated hard stops or riding the brakes down a long incline, disc brakes take longer to lose effectiveness (a condition known as brake fade). Disc brakes also perform better in wet weather, because centrifugal force tends to fling water off the brake disc and keep it dry, whereas drum brakes will collect some water on the inside surface where the brake shoes contact the drums.

Bleeding

1 Clean out reservoir

2 Top up with new Fluid

3 Select DOT

4 open bleeder nipple

5 place block under brake pedal

6 pump 6 times, hold down.

7 Open nipple and close again

8 Pump 6 times and hold down

9 Open nipple and close again

Factors when considering brakes

1 Weight
2 Speed
3 Road surface
4 Tyre condition


Working principle

1 General principle kinetic to heat energy
2 Force on the brake pedal.
3 Forces the push push rod in the brake booster which in turn forces the primary piston in the master cylinder forward, the fluid pressure presses on the secondary piston
4 The brake pipes carry the fluid pressure to proportioning valve then to the brake caliper
5 The piston forces the brake pad against the Disc-Rotor
6 The friction reduces the rotor speed
7 The wheel being attached to the rotor is there fore slowed down.