Steering and Suspension

S.A.I. – Steering Axis Inclination

1. Typical 5° - 8° on SLA

2. Typical 9° – 15° SAI on MacPherson

3. Not a tire wearing angle

4. Tilting of steering axis compared to true vertical

5. Not adjustable – built into steering knuckle

6. Provides for steering wheel returnability

Example: A car has maximum caster.

Added SAI, so it has added returnability and no tire wear.

· A tech notices caster is nonadjustable. Why is caster

Not as important as it used to be? Because of added SAI

provides steering wheel returnability.

· SAI lifts the car as you turn either direction.

MACPHERSON STRUTS

· Replace bearings

· Replace upper strut busing (possibly)

· Usually just replace struts – reuse springs/coil

- Look for oil

- Recommend gas filled strut , helps ride feel

· Put in spring compressor to loosen nut at top

- Mark when you remove

· May be able to buy cartridge to rebuild strut.

· Tubing cutting – muffler tool – strut tool

· Oil in, leave room for expansion

Terms: Alignment Equipment

Vernier caliper - specs

Tread depth gauge - video - guidelines

Flare nut wrench Valves as hydraulic brake system

Helicoil Battery charging

Thread pitch gauge Composite, hubed, hubless rotor

Hand impact driver

Toe adjustment

LAB PRACTICAL

· 5 Minutes per station, 11 stations

· Measure 3 drums

· Measure rotors

· Install drum on lathe – can you do it? Yes or no.

· Vin – build date, assembly plant location, etc…find info about vehicle

· Drums set up – shoes which way on duo servo?

(Primary to front; secondary to back; non servo, servo)

· Identify steering arm and any steering linkage

TOE

· A horizontal line through tire centerline

· Last adjustment to be made

•Greatest tire wearing angle

•The distance between the front of the tires compared to the distance between the rear of the

same tires.

•Parallel = “0”

•Toe “in” equals Positive

•Total Toe (sum toe)

•Individual Toe, compare toe of one tire to imaginary centerline of vehicle

•Toe can be measured in DEGREES, or INCHES, or MILLIMETERS

•Measurement in inches or millimeters consists of the difference between the front and the rear of the tires

•When measured in degrees, it is the difference between the vehicle centerline and the wheels true plane of rotation or centerline.

• .125 (1/8th inch) off scuffs a tire 11 ft. sideways per mile (depends on tire diameter)

Excessive toe-in (positive) will scuff the outside of the tire

Excessive toe-out (negative) will scuff the inside of the tire

The sidewall flexes in the direction of the toe setting

NOTE Common wear with bias ply tires indicate a saw tooth pattern

3 reasons for a straight steering wheel:

· Psychological

· Center to center travel of gear box

· Proper turn signal cancellation

To straighten steering wheel, put on alignment equipment, adjust tire rod ends, lengthen one, shorten other.

Turn signals – tabs built under steering wheel actually cancel turn signals operation. If wheel isn’t straight, premature or no cancellation will occur

The Ackerman Principle or Toe out on turns (TOOT) is necessary because the inner wheels turn at a sharper radius than the outer wheels

•

Provided by angled steering arms

Adjust wheels evenly to left or to right.

Low side turn – whichever side is lower, which wheels are straight is the way the tires need to be turned.

TOOT – Toe Out On Turns

· Front wheels toe out during turns

· Inside wheel will turn sharper – this is to minimize tire scrub during turns

· Aka turning radius

· 2 Types

1. Symmetrical

2. Non-symmetrical

· Because of offset engines

· To minimize torque steer – pull during acceleration

· Won’t see often

· As you turn, the angle between the steering arm and inner tie rod en becomes less, straightens out

· Angled steering arm – What physical part provides for TOOT? Angled steering arm.

Steering arm – connects to inner tie rod and part of knuckle.

Springs – 3 types:

1. 1. Leaf Spring – bends, flexes

2. Coil – compresses

3. Torsion Bar – twists

Torsion Bar – can be longitudinal or transverse (side to side)

· One advantage, it is adjustable by torquing down on the bolt, torques bar up more

· Do not want to interchange from side-to-side

Leaf Spring – main leaf with eyelet

· Shackle allows leaf spring to change length or

Straighten out during jounce and rebound

· Multi-leaf – connected with center tie bolt, holds leaves together;

Locate where rear end should be

Biggest reason tie bolt breaks is improper tightening of U-bolts.

· Avoid removing main leaf [Drawing]

· When measuring, measure from hole

· Don’t heat up – changes temper of steel

· Tie bolts come longer, put nut on before you cut, but on springs first

SPRING

· Spring rate – how much force it takes to compress spring ONE inch

· 2 Types::

1. Constant rate – stays the same

2. Variable rate – initial rate is low, but as it is compressed more, it becomes stiffer

Aka – cargo coil

· Convolutions or rings of a spring:

- If convolutions are same – constant

- If vary in distance – variable

· To raise a car with leaf springs:

1. Extend shackles

2. Add new leafs – which will provide a rougher ride

· Springs

1. New Springs

2. Spring expanders – only but 2 in. within 45° of spindle

They are to be mounted on 2 separate convolutions

CAMBER

•Tire wearing angle

•Inward and outward tilt of the tires

•Negative when the top is tilted “in”

•0 degrees when vertical

•Typical ranges from 1/4 to 1/2 degree positive

Positive camber provides directional stability

•Projects vehicle weight to inner wheel bearing, which decreases lever effect of the spindle

Negative camber projects vehicle weight away from the inner wheel bearing

•This decreases directional stability

•Results in excessive road shock and a reduction in ride quality

CASTER

1. Returnability

2. Directional Stability

· Normally specified positive, extensive because skinny

· Frame angle

+ Frame angle – higher in back

- Frame angle – higher in front

· Manual – lower caster spec.

· Power Steering – higher power steering

TURNING ANGLES

20deg. inside wheel and 18deg. Outside wheel shows 1 1/2° difference

SAI – Returnability – directional stability, enhanced road isolation

Spindle Arc –

SAI+ camber = included angle (IA)

front wheels be straight ahead prior to measurement for accurate results

3 Alignment Types

· Geometric centerline – obsolete

· Thrustline – non adjustable rear suspension

· Total 4 wheel alignment – adjustable rear suspension

NEGATIVE

Thrust Angle

Set-back - as close to 0 as possible on front wheel – is farther back than other or forward

- right wheel to back – positive setback ; will effect caster

RACK AND PINION

Never replace with original equipment.

Rack - flat gear

Pinion – round gear

· Has a torsion bar – only common link between steering wheel and tires

- Built into spool valve – rises need for assist

- Senses how much resistance at tires during turning

· In cold weather square cut seals may push to outside – high pressure

- Will start to wear soft aluminum inside housing

· Can buy long or short – with or without tie rods, etc.

· Inner and outer tie rod ends

POWER STEERING

· If you have problem with power steering, check belt tension

· Pump can put out 0-1400 psi, (All are approximate pressures)

Idle = 100 psi

Highway Driving while turning = 200 psi required

Parallel Parking = 500-600 psi required

· Power steering fluid has higher temp and pressure rating than transmission fluid

Clockspring

· Don’t wind up too tight

· For airbag

· So, don’t turn steering wheel when removing a rack and pinion

Electrical Switch in Power Steering Circuit – pressure switch, opens up circuit to AC air compressor at maximum pressure

Stabilizer Link –New style that can be damaged by spinning with air tools:

Example Intrepid, Toyota

· Some are not interchangeable

· Can make noise

Coil Springs and Stabilizer Bars

· Smaller springs will have more body roll

· The smaller coil springs, the bigger the stabilizer bar

Sector Lash Adjustment (Gear Box)

3. Sector shaft – changes rotary motion to reciprocating motion

- Teeth on second gear are tapered

- Teeth mesh with recirculating ball nut

· Tapered – so when you move shaft up, there is more clearance;

- Move shaft down, less clearance

- You want some clearance or lash, only a small amount

· Procedure: This is subject to actual manufacturers service procedures.

· Straight ahead position (wheels), middle of gear box is tightest point

· Loosen lock nut and lightly bottom out shaft and back it out half a turn

· Lock it down, test drive to make sure that

there is no binding.

When removing Pitman Arm:

1. Never hit on sector shaft, or use pickle fork

2. Sector shaft is tapered

3. Soft aluminum side cover supports sector

shaft – you could strip threads

4. Why is a Pitman Arm puller so short and stout?

It uses brute force twisting motion to separate; other pullers use the force of the puller plus

hitting it to separate components.

Rack and Pinion Steering Never put any rotational twisting force on a rack and pinion when removing a tie rod

Flex coupling – acts as a U-joint and to minimize vibrations from pump to steering wheel.

3. Any looseness is too much on a rack

4. Considered to be a weak system – doesn’t have

angles to dissipate movement like a parallelogram

linkage does and don’t forget inner tie rod looseness.

· What looseness we could get by with in the past on SLA suspensions will cause vibration or shimmy on rack and pinion steering systems.

RACK AND PINION- backlash adjustment

5. Adjustment:

1. Straight ahead position

2. Loosen lock nut

3. Bottom out adjusting plug lightly- back out ½

turn (still spring loaded with very little clearance)

If there were any imperfection in the rack, turning could create a bind or tight spot.

This design eliminates binding because spring can flex to prevent bind up.

· In Ford, you take shims out to decrease back lash

Hidden Toe Change – toe change due to looseness in suspension while driving. This is caused by loose idler arms and other looseness. Having two idler arms really increases toe change.

Purging a Shock – getting air out

· Expand a few times and compress before you put in a car

· Shock absorbers are used to control spring oscillation and not to support the car.

· When to replace?

1. Oil leakage out of shock

2. Time, lots of miles

3. If it bounces more than it should (this is

hard to tell)

· Consider replacing with gas filled shocks

· 50/50 shock – as hard to pull out as it is to pull in

like used on a steering dampener.

70/30 shock ratio, 1^st number is extension and

second number is rebound. This is by engineering

information. Racetrack guys usually refer to this ratio

backwards from what engineers do.

70 - Rebound – out or extension of shock.

/ 30 -jounce - in, compression of shock

At the track, a 90/10 shock on the front would allow the front end to come up easily and go down slower.

Purpose of SLA: Minimize tire scrub during jounce & rebound. This will allow the camber to change during jounce and rebound but will minimize side-to-side scrub of the tire during this movement. The normal or acceptable camber change is called camber arc and is sometimes around 1 ½ degrees during jounce and rebound.

Importance of Proper Ride Height Ride height measurement is really determining the angle of the suspension components (like lower control arm position)

Whatever you do to one side of car, it will try to do the opposite to the other.

- Because of weight transfer

- Whether side-to-side or front/back

Usually when the driver sits in the driver’s seat, the left camber will increase and the right camber will decrease.

· If you do not have proper ride height, you will not be able to minimize

the tire scrub during jounce and rebound which is designed into the system at the factory.

· Lowered or raised suspension will cause the tires to wear more than they would with proper ride height. This changed condition puts the suspension (control arms) at different angles and causes the ball joint to travel at different locations of the arc which causes more side to side movement, thus more tire wear.

· Rolling radius –measuring from the middle of tire to ground. This is used to insure that are of the same size. This method takes into consideration the flat spot on the bottom of the tire, which is hard to measure otherwise.

Some vehicles

· Measure ride height – Some systems like the Chevrolet truck will have the technician measure ride height and compensate with different caster specs. This allows for different frame angles because of different loads the truck in subjected to. As and example, two identical trucks might be used with different weight in them.

Best way to Lower Vehicle – drop spindle, which is really a spindle raised higher on the knuckle. This allows the control arms to remain at proper angle while changing ride height.

Main purpose of shock – control spring oscillations; it it does not hold up the vehicle!

· The spring of SLA must be stronger than McPherson,

Due to position of spring. The SLA spring is usually located ½ way out to the ball joint so you could assume the spring needs to be about twice as strong as the weight at that corner of the vehicle.

· The smaller the coil spring, the larger the stabilizer bar is what is usually recommended.

Scrub Radius – distance between 2 lines at the pavement. These two lines are the projected centerline of the tire (camber) and the steering axis (same as included angle). If they meet below the pavement, it is called positive scrub radius. If these two lines meet above the pavement, it is called negative scrub radius. The actual scrub radius is the distance between these two lines at the pavement.

Scrub Radius on SLA – typically have positive scrub radius = lines intersect below the surface;

This tends to toe out

Scrub Radius on McPherson Strut – negative scrub radius

· Lines intersect above surface

· Tends to toe in

· Where the two lines intersect, either above the pavement or below

· Uses same 2 projected lines as included angle

· As long as you have even braking, no problem

· ABS – one pulses, steering wheel would turn, so they decreased the scrub radius to minimize steering pull while in abs function. (As it is pulsating brakes)

· Deep dish, low profile

Offset wheels and low profile tires will change the scrub radius

If Scrub radius changes because of different wheel installed – can’t promise that it will handle as it was designed.

SAI- Steering Axis Inclination Typical

SLA - 5°- 8°

McPherson Strut - 9° - 15° or more

Is built into the steering knuckle and is not adjustable. Will aid in steering wheel return ability. I considered a non tire-wearing angle. SAI will tend to raise up each side while turning either direction. Increased SAI now does more to help return the steering wheel to straight ahead position so as not to depend on so much positive caster which is a cause of camber roll.

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