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Chassis Systems.
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Steering Geometry. 05-09-2004

by Frans Deguara.

 

Steering Geometry. 

The steering geometry of a vehicle has an important effect on how the vehicle steers and handles. These angles are; a) Castor angle, b) Camber angle, c) Swivel Pin Inclination (KPI).

 

Castor angle. is formed in the suspension by tilting the Swivel Pin backwards at Top. The vertical axis of the Swivel Pin / King Pin is up to about 5 but up to about 9 on very short wheelbase cars. Inclining the King Pin in this position results in a so called Positive Castor. Positive Castor has a positive effect on the steered wheels as the road wheels are able to self-centre in all forward driving conditions. Yet, it has an adverse effect when reversing.

 

Camber angle.  The Stub Axle of the road wheel is usually slightly tilted by a few degrees from the horizontal to give either Positive, Zero or Negative Camber to the wheels. Thus, when the Front wheels are set at 90 to the ground they have Zero Camber. Tilting the Top of the wheel inwards (to the centre of the car) produces Negative Camber and vice-versa.

The purpose of Cambered wheels is to enable the steered wheels to swivel more easily, giving light and easy steering (especially with Pos. camber).

 

KPI. This is the angle that the Swivel Pin is inclined from the vertical when viewed from the front of the vehicle. KPI helps the steering to centre again and also it reduces stress on the steering components.

 

Ackermann Angle. This ensures that true rolling is produced when the front wheels are steered thus eliminating tyre scrub and less effort on the steering wheel.

 

Centre Point Steering. This results in reduced steering effort very needed on heavy vehicles. Centre Point Steering is produced when the KPI axis and the Cambered wheel axis intersect at a point where the tyre touches the ground.

 

Steering Gear.  Three main types are in common use :- 

a) Worm and Peg, b) Recirculating Ball, c) Rack and Pinion.   

 

Whichever system is in use, the system must posses some degree of Reversibility, that is, some feedback of the road conditions are directed back to the steering wheel. It also must ensure the minimumamount of Backlash or Free-Play at the steering wheel.

In most cases, gear oil is used to lubricate non-PAS gearboxes.

On All IFS systems, Three (3) Track-rods connect the steering box to the wheels. In the Rack and Pinion system, the Rack replaces the Centre Track-Rod piece.

 

The Steering Column. This is usually made up of a number of steel shafts which are Offset Connected  to each other (often in a Z shaped centreline) for safety reasons in-case of a front-end collision. Flexible couplings and / or compact Universal joints connect these shafts in different planes.

 

Ball Joints. These link Two (2) components together. Yet, they allow angular and rotaional movement between them. This feature makes them ideal to be used as Swivel-Pins on IFS.

 

Power Assisted Steering.  (P.A.S.) :- The requirements of a PA System is to :-

a)       Reduce Drivers effort.

b)       Be Fail-Safe

c)       preferably be Speed Sensitive.

d)       can operate also if the assistance fails.

 

Suspension Springs.  An important part of the suspension is the spring. Three main types of springs used are the coil spring, leaf spring and torsion bar.

   Coil springs and torsion bars are generally used in the front whereas leaf springs are generally used in the rear in RWD layouts. Coil springs are generally installed between the upper and lower wishbones with the shock absorber mounted inside the spring. In some cases the coil spring is mounted on top of the upper control arm and a spring tower formed in the front-end sheet metal. Coil springs come in many "rates" and can be used to change the handling and ride characteristics of a vehicle.

   Leaf springs are made from layers of spring steel bolted together through the center of the leafs. This center bolt locates the spring to the axle casing and is attached to it with large U bolts. The ends of the leaf spring are attached to the frame or body through a shackle that allows the spring to flex without tearing or breaking out. The leaf spring also acts as control arms to keep the axle casing in its proper position.

Troubleshooting Steering & Suspension Problems.

         Car pulls to one side while driving:
As you drive along the car tends to pull to one side or the other. So you need to constantly hold the steering wheel firmly to keep the car going straight. Possible causes are :-

1.       Tire pressures are not equal: Check and adjust tire pressures.

2.       The wheels are out of alignment: Have the wheels aligned.

3.       One brake is dragging or not releasing: Check the brakes and repair as required.

4.       Parts of the steering linkage are loose and need to be tightened or replaced : -Tighten or replace parts as required.

5.       The car's tires are not worn evenly: Replace tires as required.

         The vehicle wanders down the road:
Constantly correction is required in directing the car by turning the steering wheel.

Possible causes :-

1.       The car is overloaded, or the weight is unevenly distributed: Lighten the load or equalize weight distribution.

2.       The wheels are out of alignment: Have the front wheels aligned for equal Castor, Camber and Toe-Out on Turns. (Toe-In or Toe-Out as required).

3.       The car's springs and dampers are weak: Replace springs and/or dampers as required.

4.       Parts of the steering linkage are loose or worn out: Tighten or replace worn parts as required.

5.       The front wheel bearings are out of adjustment or are severely worn: Adjust wheel bearings or replace as required.

 

         Jerky Steering Wheel:
Driving slowly or at an idle the steering wheel jumps or jerks. Fault may become worse as time goes.

Possible causes:

1.       The power steering drive belt is loose or damaged: Adjust belt tension or replace power steering drive belt as required.

2.       The fluid level in the power steering reservoir is low: Fill fluid to proper level.

3.       The engine is idling too low: Adjust idle speed.

4.       Defective power steering pump: Repair or replace power steering pump as required.

5.       The steering linkage may be rubbing against something: Inspect steering gear mechanism and repair the interference.

 

         Steering wheel vibrates:
The steering wheel begins to vibrate at a constant medium speed. (60-85k/h). You also notice that the steering wheel / the car is also vibrating.

Possible causes:

1.       Warped or damaged brake discs and/or drums: Resurface or replace the brake discs and/or drums as required.

2.       Loose wheel nuts: Tighten wheel nuts.

3.       Out-of-balance wheel and tire assemblies: Balance wheels.

4.       Loose or worn steering linkage parts: Tighten or replace parts as required.

5.       Bent or damaged wheels and rims: Replace bent or damaged wheels.

6.       Severely worn or damaged tires: Replace tires.

 

         Wheel shimmy:
Side-to-side steering wheel wobble when traveling at steady speeds. The vibration gets worse when you are on an uneven road surface or after going over a pot hole.

Possible causes:

1.       Unequal Tire pressures: Check and adjust tire pressures.

2.       Out-of-balance wheel and tire assemblies: Balance wheels.

3.       Worn or damaged tires: Replace tires.

4.       Parts of the steering linkage are loose, worn or need to be tightened: Tighten or replace worn / loose parts as required.

5.       Worn suspension parts: Replace suspension parts as required.

         Noises while turning a corner:
A knocking, clunking, and/or squeaking noise is heared while driving around a corner. Otherwise, all else seems to be good except for the noise.

          

         Possible causes:

 

1.       Loss of lubricant in the steering gearbox or needs to be repaired or adjusted: Lubricate or replace steering gear parts as required.

2.       Parts of the steering linkage are loose, need to be tightened, adjusted or re[placed: Tighten, adjust or replace parts as required.

3.       Tyres are hitting or rubbing against the body or something: Locate the interference and repair.

4.       Worn suspension parts: Replace suspension parts as required.

5.       Rubbing against or hitting the steering column: Locate the interference and repair.

6.       Defective steering column couplings and/or universal joints.

Brakes. Care for your brake systems. TT-04002

Brakes

Brakes are an essential part of your vehicle. Good maintenance is key to making sure that your brakes do what they were designed to do - keep you safe by stopping your vehicle.

Free Brake Inspection

At any time during normal business hours, you can go into your car servi-centre with an appointment for a brake - anti-lock and regular - inspection. One certified technician will examine your entire brake system -- pads/shoes, hydraulic fluids, anti-lock systems, rotor/drum wear and calipers. Then he will tell you what, if anything, is needed to be replaced.

Pads and Shoe Replacement

You must use only reliable replacement parts from the makers of Brake components that meet or exceed your vehicle manufacturer's specification in WARRANTY STATEMENTS

Resurface or Replace Rotors or Drums

To ensure your brake rotors (discs) or drums have a clean, even surface -- necessary for proper braking, the garage will resurface or "turn" them, keeping the rotor/drum within your vehicle manufacturer's recommended specifications for minimum thickness. If they need to be replaced, then the technician will tell you up front and provide a written estimate too.

Bleed and fill hydraulic system

Sometimes braking can become unsteady due to air bubbles in your vehicle's hydraulic brake line. By 'bleeding' your brakes, you will remove troublesome air bubbles and refill your hydraulic brake fluid to the manufacturer's recommended level with hydraulic fluid that meets or exceeds your vehicle manufacturer's specifications.

Other Brake Services

Certified technicians must be able to perform all the work necessary to ensure your brakes perform at their best. This includes installing master cylinders, all brake hoses, brake cables, wheel cylinders and re-packing wheel bearings. All of these services will only be performed if necessary. You will be given a complete description of what needs to be done and a comprehensive cost estimate before any work begins.

 

 

Get the Brake Service that's right for you!

Choose from these four brake service options

Basic
1 yr/ 12,000 mi
pad guarantee

Standard
2 yr/ 24,000 mi
pad guarantee

Premium
3 yr/ 36,000 mi
pad guarantee

Deluxe
Lifetime pad & caliper guarantee

Replace disc pads

Clean & lubricate caliper mountings

Resurface rotors

-

Replace pad & caliper hardware

-

-

Install factory remanufactured calipers

-

-

-

Bleed & flush hydraulic system

-

-

-

2WD, 4WD and AWD.

2-Wheel Drive.  The engine, clutch and gearbox are usually mounted on the frame at the front of the vehicle. The rotating motion produced by the crankshaft at the front of the vehicle is transmitted either to the two wheels at the rear (rear wheel drive), or the two wheels at the front (front wheel drive). Some cars are manufactured with rear mounted engines that drive the rear wheels, and front mounted engines that drive the front wheels. 4 Wheel Drive 4-wheel drive vehicles use live front and rear drive axles. When the front drive axle receives power from the transfer case, along with the rear drive axle, the vehicle can function well on off-road terrain (sand, rocks, mud, snow, etc.). A 4-wheel drive vehicle has one drive axle that is automatically in use. The operator of the vehicle has to activate and deactivate the second live drive axle. All Wheel Drive (AWD) All-wheel drive vehicles use live front and rear drive axles. When the front drive axle receives power from the transfer case, along with the rear drive axle, the vehicle can function well on off-road terrain (sand, rocks, mud, snow, etc.). A 4-wheel drive vehicle has one drive axle that is automatically in use. The operator of the vehicle has to activate and deactivate the second live drive axle. An all-wheel drive vehicle has both axles live at all times without manually activating or deactivating axles.

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