Heavy Duty Suspension Systems

The primary function of a heavy duty truck suspension system is to:

Increase engine horsepower Support the vehicle load, maintain axle alignment and provide ride control Control steering geometry only Lubricate wheel bearings

Leaf spring suspensions are commonly used because they:

Provide only cosmetic value Support load, locate the axle and help control ride height Eliminate the need for shock absorbers in all cases Cannot be used on tandem axles

Multi-leaf spring packs are typically clamped together using:

Shock absorbers Centre bolts and clips Steering knuckles Brake chambers

Equalizer beams (walking beams) on tandem suspensions:

Support only one axle Distribute load between axles by pivoting between them Control steering only Are used only on front axles

Torque rods or radius rods are used in heavy duty suspensions to:

Transmit engine power to the wheels Control axle position, prevent wind-up and maintain alignment Adjust tire pressure Support cab weight

Rubber bushings in suspension torque rods:

Provide flexible connections that absorb vibration and allow limited movement Are used only for decoration Eliminate the need for fasteners Support engine mounts only

Air ride suspensions use:

Leaf springs only Air springs (air bags) in place of or in combination with steel springs No springs at all Only rubber blocks

Ride height control valves on air suspensions:

Control engine speed Automatically add or exhaust air from the suspension to maintain design ride height Control brake application Operate windshield wipers

Improper ride height on an air suspension can:

Improve driveline angles Cause poor driveline angles, uneven loading and handling problems Have no effect on component life Increase brake efficiency

Shock absorbers on heavy duty suspensions are primarily used to:

Support static vehicle weight Control spring oscillations and dampen suspension movement Adjust brake timing Lubricate bushings

Walking beam suspensions are often used on:

Light-duty front axles only Heavy vocational trucks requiring high articulation and durability Passenger cars only Trailers without axles

Parabolic leaf springs differ from conventional multi-leaf springs because they:

Use many leaves of equal thickness Use fewer tapered leaves to reduce weight and improve ride Are made only of rubber Cannot be used on drive axles

Air bag (air spring) replacement parts selection must consider:

Only overall height Correct style, diameter, capacity, mounting studs/plates and port size Colour of rubber Any similar appearing unit

Helper springs or overload springs are installed to:

Reduce load capacity Increase load-carrying capacity when vehicle is heavily loaded Control steering alignment Reduce tire size

A main function of suspension alignment is to:

Increase exhaust back pressure Keep axles square and parallel to frame for good tracking and tire wear Adjust fuel economy only Support cab mounting

Suspension hangers are components that:

Mount to frame rails and support spring or walking beam pivot points Support engine mounts Hold mud flaps only Connect to steering gear

U-bolts in heavy duty suspensions are used to:

Hold rims to tires Clamp axle housings to spring packs or suspension beams Adjust brake stroke Support cab steps

Loose or improperly torqued U-bolts can lead to:

Improved alignment Axle movement, misalignment and potential component damage Better fuel economy Reduced tire wear

Rubber block suspensions use:

Only leaf springs Solid rubber elements to support load and provide damping Only air springs Water-filled springs

The ILM Heavy Duty Suspension Systems module expects parts technicians to:

Perform complete suspension alignments Identify suspension types, key components and correct replacement parts Design new frame rails Adjust transmission ratios

On many tandem drive suspensions, the 'torque rod' adjusts:

Brake balance Axle alignment and thrust angle Engine idle speed Air pressure in the tires

Equalizer bushings and pins should be replaced when:

They are new They show excessive wear, play or damage affecting ride and alignment Any suspension component is painted Shock absorbers are changed

A chassis with a rear suspension 'dog-tracking' (crabbing) typically indicates:

Perfect alignment Axle misalignment relative to the frame Correct tire balance Proper ride height

Suspensions designed for off-road and dump trucks often emphasize:

Maximum ride comfort only Durability, high load capacity and articulation over smooth ride Very low load capacity No equalization between axles

Air suspension leveling valves are normally mounted:

Directly on the differential housing On the frame and linked mechanically to the axle or suspension Inside the cab On the engine block

Overloaded suspensions can result in:

Reduced tire wear Spring breakage, bushing failure and frame damage Improved ride quality Lower brake temperatures

Progressive-rate suspensions are designed so that:

Spring rate decreases with load Spring rate increases as the spring deflects, improving loaded stability Spring rate stays constant Shocks are eliminated

When ordering suspension parts, critical information includes:

Driver’s name only Vehicle make, model, axle configuration, suspension model and serial if available Cab colour Tire brand only

A heavy-duty air suspension often includes:

Only one air bag Air bags, leveling valves, radius rods, shocks and frame/axle brackets Leaf springs only No linkages

Frame brackets and hanger brackets must be:

Interchanged from any truck Matched to the suspension design and frame hole patterns Drilled randomly for mounting Made of soft material for flexibility

A common symptom of worn suspension bushings is:

Sharper steering response Clunks, poor tracking and irregular tire wear Lower fuel consumption Higher brake efficiency

Reduced shock absorber performance can cause:

Improved handling Excessive bouncing, poor ride and increased wear on other suspension parts Lower tire temperatures More stable braking

'Lift axles' or 'tag axles' in some suspensions are used to:

Decrease load capacity Add or remove axle load capacity depending on road and load conditions Control steering Replace drive axles

Suspension specifications in the ILM help parts technicians:

Set legal load limits Identify correct springs, bushings, torque rods, hangers and fasteners Adjust transmission ratios Select engine horsepower

Rubber rebound stops (bump stops) are used to:

Increase maximum suspension travel Limit suspension compression travel and protect components Adjust brake balance Support exhaust systems

Heavy-duty suspension components are often rated by:

Cab size Axle load capacity in kilograms or pounds Paint thickness Tire brand

In air ride suspensions, air leaks can lead to:

Stable ride height Sagging ride height, compressor overuse and poor handling Reduced brake wear Improved fuel economy

On vocational trucks, steel spring suspensions are often chosen because they:

Are lighter and smoother than all other types Are robust, simple and tolerant of harsh loading conditions Require no maintenance Eliminate axle hop under braking