PMI Discrepancies on a High-Mileage Sleeper
A 2015 sleeper tractor with 612,000 miles comes in for a scheduled PMI. The previous inspection sheet (90 days ago, 598,000 miles) noted: left steer tire at 6/32", right steer at 7/32", front brake lining at 40%, rear drive linings at 25%, and a "minor" power steering seep at the gear box. Today: left steer 4/32", right steer 6/32", front linings 35%, rear drive linings 12%, and the steering box seep now leaves a dime-sized drip overnight. The driver mentions a slight pull to the left and a shimmy at 55–60 mph. The shop's PMI form has a checkbox for "brakes OK" and "tires OK" with no measurement fields.
1. Identify which findings require action before the unit is released and justify each against the trend data, not just the current number.
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Left steer tire - action required. 6/32→4/32 in 14,000 miles is accelerated wear (2/32 in 14k vs. right steer 1/32). At that rate the tire reaches the 4/32 steer-axle pull point almost immediately. The uneven left/right wear plus the pull-to-left symptom points to alignment or a dragging left front brake, not normal wear. Do not release on this tire without diagnosis.
Rear drive linings - action required. 25%→12% in 14,000 miles is a steep wear rate; at that rate the linings reach condemnation in roughly another 10–15k miles. More importantly, the rate itself is abnormal and suggests dragging brakes, a hung slack adjuster, or overload. Inspect before release.
Steering box seep - action required. A "minor seep" that now drips overnight is progression, not a stable condition. Loss of power steering fluid is a steering-control hazard and can damage the pump. Diagnose the seal; do not simply top off.
Shimmy at 55–60 mph - ties to the tire/alignment findings and must be resolved; a shimmy is a steering and tire-failure risk.
Front linings 40%→35% is normal-rate wear; monitor.
2. The PMI form has only pass/fail checkboxes with no measurement fields. Explain why this is a documentation problem and what the technician should do.
Read the worked answer
Pass/fail checkboxes cannot capture trend, which is what drives the decisions above. A 12% lining that was 25% three months ago is a very different risk than a 12% lining that was 14% - but both check the same box. The form also cannot defend the technician if a failure occurs, because there is no record of the measured value or the date.
What to do: Record actual measurements (tire tread in 32nds per position, lining thickness per wheel, fluid levels, leak descriptions with drip size and location) in the notes or on an attached sheet, with date and odometer. Flag any item whose rate of change is abnormal, even if the absolute value passes. Note the driver complaint and what was done about it. Recommend the shop revise the form to include measurement fields and a "previous reading" column - this is a legitimate process-improvement recommendation, not overstepping.