Suspension System Diagnosis and Repair - B Flashcards
Describe heavy-duty front axles.
Heavy duty front axles are forged solid I-beams. - The axle is mounted to the leaf springs and retained with U-bolts.
How would you inspect an axle?
- Perform a thorough visual inspection to identify looseness and shifted or broken parts. - Inspect the U-bolts and shims for proper torque and placement. - Measure the front wheel set back on both wheels and compare because a difference in measurement could be caused by a bent axle, or worn, misaligned components (i.e., spring eye bushings) - Check the axle for twist using a machinist’s protractor. - Check the axle for twist using a machinist’s protractor. - If the front axle must be removed, pay particular attention to spacers and castor shim placement. - Be sure to mark the front of the axle to ensure proper placement when reinstalled. - Always replace the U-bolts. U-bolt threads stretch during initial installation and scale and rust buildup may prevent improper pull-up torque and insufficient clamping force.
Describe kingpins and their function.
- Some OEMs refer to the kingpin as a knuckle pin. - Kingpins may be a straight or tapered design. - Kingpins connect the I-beam to the steering knuckle and act as pivots to turn the front wheels.
What could a loose kingpin or kingpin bearing cause?
Could cause a shimmy with slight vibrations. - A dial indicator is used to measure vertical play, upper and lower bushing free play, and upper and lower bushing torque deflection in the knuckle.
How would you adjust vertical end play?
Is adjusted by adding or removing shims to obtain the manufacturer’s clearance specification. - If the bushing free play measurements are out of spec, the bushings and kingpin will need to be replaced.
How do you grease a front axle kingpin?
- Place a jack under the front axle and raise the vehicle to unload the suspensions. - Grease the upper bushing until grease appears between the steering knuckle and the top of the axle eye. - Grease the lower bushing and continue greasing until grease begins to leak out through the pivot bearing. - This shows a thorough distribution of the grease.
What should you do when replacing the kingpins?
- Remove the upper and lower knuckle caps to access the kingpins. - Remove the draw key nut and drive out the draw key. - Then press out the kingpin from the knuckle. - Prior to assembly, check the axle eye bore for wear.
What does the draw key do?
The draw key keeps the kingpin aligned and tight in the axle bore. - When reassembling the assembly, torque the draw key nut to the manufacturer’s specification. - The draw key torque should also be checked at every preventive maintenance inspection.
What happens when a vehicle hits a bump?
The wheel and suspension move upward in relation to the chassis. - This causes jounce and rebound.
What do shock absorbers do?
Shock absorbers dampen or control spring action from jounce and rebound, reduce body sway, and improve directional stability and driver comfort.
What happens with worn-out shock absorbers?
Worn out shock absorbers, will allow the front end to bounce, causing the steering wheel to shake for a few seconds. - The piston sheild often gets bent or damaged and will scrape against the shock absorber when the suspension moves up and down. - Shock absorbers stop spring oscillation and are still needed on air spring suspensions.
How should you inspect shock absorbers/
Should be inspected for loose mounting bolts and worn mounting bushings. - If these components are loose, rattling noise is evident, and replacement of bushings and bolts is necessary. - In some shock absorbers, the bushing is permanently mounted in the shock, and the complete unit must be replaced if the bushing is worn.
What is the result of worn mounting bushings?
The shock absorber will not provide proper spring control, and rattling will occur when driving over road irregularities.
What happens if you find oil leakage in shock absorbers when inspecting?
A slight oil film on the lower oil chamber is acceptable. - Any indication of oil dripping is not acceptable, and unit replacement is necessary.
What should you visually inspect shock absorbers for?
For a bent condition and severe dents or punctures. - When any of these conditions are present, unit replacement is required.
How should you manually test shock absorbers?
When this test is performed, disconnect the lower end of the shock and move the shock up and down as rapidly as possible. - A satisfactory shock absorber should offer a strong, steady resistance to movement on the entire compression and rebound strokes. - The amount of resistance may be different on the compression stroke compare with the rebound stroke. - If a loss of resistance is experienced during either stroke, shock replacement is essential.
What should you do if you have a defective shock absorber that has internal clunking, clicking, and squawking noises, or binding conditions?
Shock absorber replacement is necessary. It is advisable to replace shock absorbers in pairs.
What is a leaf spring?
A leaf spring is a spring assembly where the individual leaves are the same width for the whole length of the assembly.
What are parabolic springs?
Parabolic springs are assemblies where the leaf width is usually greater at the center of the spring, and the width decreases toward the outer end of the spring.
How is a taperleaf spring classified?
A taperleaf spring is classified as a parabolic spring since the leaves are thicker in the center, and the thickness decreases toward the end of the leaf.
What are the steps to take when inspecting the leaf/parabolic spring assemblies?
- Look for broken or shifting leaves in the spring pack. - Inspect the front and rear shackle spring pins and bushings for wear. - Inspect the U-bolts, spring seats, and top plates for looseness or wear.
The suspension system should be inspected periodically to ensure vehicle safety as part of a regular maintenance schedule recommended by the truck manufacturer or owner. What components should you check?
_Inspect the tires for excessive tread wear. -Check the torque on the wheel nuts, and inspect the wheel rims for damage. - On rear suspension systems, inspect all torque rods for damage or a bent condition. Inspect all torque rod bushings for looseness, wear, and deterioration. - Inspect all spring shackles, bushings, and brackets for looseness. A pry bar may be used to pry downward on the outer end of the spring to check for looseness in the shackles and bushings. - Inspect all spring U-bolts for damage and check the torque on the U-bolt nuts. - Inspect the springs for broken leaves, damaged clamps, broken center bolts, and a sagged condition. - Inspect all equalizer components for wear.
Where should you be sure each side of the drive axle housing is position?
On the same location on each spring. A broken center bolt may allow the drive axle to slide backward on the spring.
What can and will not break the spring center bolt?
Loose spring shackles will not break the spring center bolt. Loose front spring U-bolts can break the spring center bolt or leaves between the U-bolts.
What can a broken leaf spring center bolt cause?
A broken leaf spring center bolt can cause axle shifting leading to premature toe-like tire wear and steering pull. -If the spring assembly is replaced, always replace the U-bolts.
What happens to U-bolts threads during initial installation?
U-bolt threads stretch during initial installation and scale and rust buildup may prevent improper pull-up torque and insufficient clamping force.
If a defective spring assembly is identified, what should be considered?
- Whenever one spring leaf is broken, all of the other leaves in the assembly have been overloaded and running under increased stress. Consideration should be made to the age and condition of the other leaves prior to repair. - If one spring leaf is broken and the remaining leaves are deemed serviceable, it is acceptable to replace only the broken leaf, however it is advisable to replace the same leaf in the other spring pack on threat axle to ensure both spring assemblies remain matched regarding load carrying capacity, rate of deflection, and ride height characteristics. - If two or more leaves are broken in the spring pack, it is recommended that the entire spring assembly be replaced. - If the spring assembly on one side of the vehicle is being replaced, it is advisable to replace both spring assemblies across that axle.
What do torque rods, radius rods/arms, transverse torque rods, and torque leaves do?
Provide braking force absorption and allow for driveline angle adjustment and axle alignment.
What do tandem axle suspensions often have?
Four multi-leaf springs and four torque rods.
Where is an equalizer hanger (center hanger) mounted?
Is mounted to the frame between the front and rear springs on each side of the tractor. - The springs ride on an equalizer pivot beam mounted on a sleeve in the equalizer bracket.
What may be substituted for rear shock absorbers?
Torque rods. - Four to six torque rods may be used on spring suspensions for suspension alignment. - Torque arms are either adjustable or fixed-length design.
How would you make rear axle alignment adjustment on a spring suspension with adjustable torque rods?
Can be made by rotating one end of the torque rod in or out of the threaded sleeve.
How do fixed-length torque arms help to align the rear axle?
Fixed length torque arms use shims between the front of the torque rod and spring hanger bracket to align the rear axle.
How do some manufacturers achieve axle alignment?
Utilize a multi-leaf spring pack equipped with a torque leaf. - In this case, an eccentric bushing at the torque leaf is rotated to achieve alignment.
How would you inspect torsion bars?
Torsion bars are the same length but are usually not interchangeable left to right. - As long as a torsion bar is not cracked or broken, it can be adjusted at the crank assembly to level the vehicle. - You never heat or bend torsion bars or torque arms.
What will premature suspension bushing wear cause?
Will cause noisy operation, directional instablilty and excessive wear to adjacent suspension components.
How would you inspect the torque arm/leaf bushings and pins for wear?
Inspect the torque arm/leaf bushings and pins for wear, cracking, and shifting. - In addition, you should check the mounting bolts and shim packs on units utilizing this mounting method. - When bushings are replaced, be sure the suspension is in a neutral state. - A bushing not relaxed during assembly can cause a binding condition leaving a vehicle off-level.
What do equalizing beam suspension do?
Equalizing beam suspension lowers the center of gravity of the axle load.
What are the two types of equalizing beam suspensions ?
The two types of equalizing beam suspensions are leaf spring type and rubber load cushion type. - In a leaf spring-type suspension, the front of the leaf springs assembly utilizes a spring pin to mount it to the front hanger. - The rear of the spring has no rigid mount allowing for forward and rearward movement to compensate for spring deflection. - The spring assembly mounts to a saddle with either U-bolts or straight bolts.
What is the function of tandem rear-axle suspension systems.
Tandem rear-axle suspension systems have equalizer beams on each side of the suspension. - The equalizer beams incorporate bushings at each end and in the center of the beam. - The equalizer beams are attached to the fron and rear axle housings and the spring saddle. - A cross tube is mounted between the two equalizer beams. - You can service walking (equalizing) beam center and end bushings on the vehicle using a special OEM tool. Multi-leaf springs are mounted on saddles above the equalizer beams.
How should you inspect walking beam suspensions?
The technician should look for beam bushing wear, spring stack shifting, loose mounting hardware, spring hanger or rubber cushion wear, and torque arms and bushings. - In addition, inspect the cross tube for wear or damage. - Wear in the cross tube may indicate worn equalizer beam bushings.
What are the recommendations if a defective spring assembly is identified.
- Whenever one spring leaf is broken, all of the other leaves in the assembly have been overloaded and running under increased stress. Consideration should be made to the age and condition of the other leaves prior to repair. - If the spring assembly on one side of the vehicle is being replaced, it is advisable to replace both spring assemblies across that axle.
