Pre-Trip Inspection: Suspension
12 questions in the bank cover this topic. Everything below is drawn from the sources those questions cite.
Sources: 49 CFR 396 Appendix A, 49 CFR 570.61
What you need to know
A spacer raises ride height without restoring spring rate, so the suspension sits right and behaves wrong.
570.61(a) treats it as a defect in itself.
Springs shall not be broken and coil springs shall not be extended by spacers.
49 CFR 570.61
Oil on the housing means the seal has gone and the shock has lost its damping fluid.
A warm shock is a working shock; a wet one is a dead one.
There shall be no oil on the shock absorber housings attributable to leakage by the seal.
49 CFR 570.61
All three.
U-bolts hold the axle to the springs, so a loose one lets the axle shift under braking and steers the vehicle for you.
Shock absorber mountings, shackles, and U-bolts shall be securely attached.
49 CFR 570.61
Cracked, extruded or missing.
A bushing squeezing out of its joint is on its way to missing, which turns a controlled pivot into metal-on-metal play. A bushing squeezing out of its joint is on its way to missing.
Rubber bushings shall not be cracked, extruded out from or missing from suspension joints.
49 CFR 570.61
570.61(a) lists all three.
A ball joint seal matters because once it splits the grease escapes and dirt gets in, so the joint is wearing fast long before it is loose enough to feel.
Ball joint seals shall not be cut or cracked, other than superficial surface cracks.
Stabilizer bars shall be connected.
Radius rods shall not be missing or damaged.
49 CFR 570.61
Any broken or missing leaf, not just the main one.
The remaining leaves now carry a load they were not sized for, so the next failure comes sooner.
Any leaves in a leaf spring assembly broken or missing.
49 CFR 396 Appendix A
Because of what it can reach.
A leaf working its way sideways into a rotating tire or drum turns a suspension fault into a tire failure or a fire.
One or more leaves displaced in a manner that could result in contact with a tire, rim, brake drum or frame.
49 CFR 396 Appendix A
Out of service.
A deflated air bag transfers its load to parts never meant to carry it and changes how the axle tracks under braking.
Deflated air suspension, i.e., system failure, leak, etc.
49 CFR 396 Appendix A
U-bolts hold the axle to the spring.
A loose one lets the axle shift under braking, which steers the vehicle for you.
Any U-bolt(s), spring hanger(s), or other axle positioning part(s) cracked, broken, loose or missing
49 CFR 396 Appendix A
Oil on the body means the seal has gone and the damping fluid with it.
A warm shock is working; a wet one is finished.
There shall be no oil on the shock absorber housings attributable to leakage by the seal.
49 CFR 570.61
Any broken or missing leaf is a defect, not just the main one, because the remaining leaves now carry a load they were not sized for.
Any leaves in a leaf spring assembly broken or missing.
49 CFR 396 Appendix A
Hangers and shackles carry the spring ends while allowing it to lengthen as it flexes.
The U-bolts clamp its center to the axle instead.
Any U-bolt(s), spring hanger(s), or other axle positioning part(s) cracked, broken, loose or missing
49 CFR 396 Appendix A
Check yourself
- Is a spacer fitted to extend a coil spring acceptable?
- What should you treat as a sign that a shock absorber has failed?
- What three suspension fasteners must you find securely attached?
- What three conditions are you looking for at the rubber bushings?
- What must you look for as a suspension defect on a walk-around?
- A leaf spring assembly with one broken leaf is ______.
- Why is a displaced spring leaf a defect even when it is unbroken?
- A vehicle whose air suspension has deflated is ______.
- The part that clamps your leaf spring to the axle is:
- On which part would oil on the housing mean it has failed?
- What must you check when looking for a broken or missing leaf?
- What is it that holds the ends of your leaf spring to the frame:
Answers are in the practice test for this topic.