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Difficulty: Very hardSuspension System Inspection

During a comprehensive pre-trip inspection of a combination vehicle, you record the following observations regarding the suspension systems:

- Left Steer Axle (10-leaf spring assembly): Two non-main leaves are fractured. The shock absorber exhibits a light condensation of oil on the lower casing, but is not actively dripping.
- Right Drive Axle (Air Suspension): You detect a faint air hiss from a fitting on the ride height control valve, but the system maintains normal compressor cut-out pressure and all air springs are fully inflated.
- Left Trailer Axle (8-leaf spring assembly): One non-main leaf is missing entirely, and another non-main leaf is cracked completely through. The torque arm bushing shows superficial surface cracking with no missing rubber.

Based on standard commercial vehicle out-of-service (OOS) criteria, which of the following determinations is correct?

  1. A
    The vehicle is legally safe to operate because no main leaves are broken, the air springs remain properly inflated, and the total leaf failure on the trailer axle remains below the 33 percent out-of-service threshold.
  2. B
    The vehicle must be placed out of service because the combined presence of a shock absorber fluid weep and an active air leak on the ride height control valve directly compromises the vehicle's dampening capability.
  3. The vehicle must be placed out of service solely because the trailer's leaf spring assembly has reached the exact 25 percent threshold for broken or missing leaves.Answer
  4. D
    The vehicle must be placed out of service because any fractured leaves on a steer axle assembly mandate an immediate out-of-service condition, regardless of the percentage.

Answer

The vehicle must be placed out of service because the trailer's leaf spring assembly has precisely 25% of its leaves broken or missing.
The correct determination is that the vehicle is out of service due to the trailer axle suspension. The regulation clearly states that if one-fourth (25%) or more of the leaves in any spring assembly are broken or missing, the vehicle cannot be driven. On the trailer's 8-leaf assembly, 2 compromised leaves (one missing, one cracked) constitute exactly 25%. The steer axle's 2 broken leaves out of 10 equal 20%, which is below the threshold, and the other noted defects (minor shock weep, minor air leak without bag deflation) do not meet out-of-service criteria.

Step-by-Step Solution

1
Evaluate the steer axle leaf spring assembly against the 25% threshold rule.
2 broken non-main leaves out of 10 total leaves equals 20%.
Since 20% is less than the 25% (1/4) out-of-service threshold, and no main leaf is broken, the steer axle suspension is legally acceptable.
2
Evaluate the steer axle shock absorber.
The shock absorber has light oil condensation (weeping) but no active drip.
Commercial vehicle guidelines distinguish between a failing shock (actively leaking) and standard wear (weeping); this condition does not place the vehicle out of service.
3
Evaluate the drive axle air suspension system.
There is a minor hiss at the control valve, but the system maintains pressure and air springs are fully inflated.
An air suspension system is only placed out of service if an air spring is deflated or a structural component is broken/missing.
4
Evaluate the trailer axle leaf spring assembly.
1 missing + 1 broken leaf = 2 compromised leaves out of an 8-leaf assembly. 28=25%\frac{2}{8} = 25\%
The Commercial Vehicle Safety Alliance (CVSA) out-of-service criteria state that a vehicle is out of service if 1/4 (25%) or more of the leaves in any spring assembly are broken or missing. The trailer axle exactly meets this threshold.

Key Concept

Suspension System Out-of-Service Criteria
Estimated Time:2m 30s
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Topics

Suspension System Inspection

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