T8 Preventive Maintenance Inspection (PMI) — practice test

High-yield T8 topics

The material that shows up year after year. If you're short on time, start here.

• Air system limits, memorized cold. Leak-down: 2 psi/min static and 3 psi/min applied for a single vehicle, 3 and 4 for a combination. Low-air warning must be on at 60 psi or above. Spring brakes apply somewhere in the 20-45 psi band. Governor cut-out 120-135 psi, cut-in about 20-25 psi below that. Build 85-100 psi in 45 seconds. They will hand you a scenario with one number off and ask pass/fail.</string>
• Pushrod stroke and lining. Know that the readjustment limit is chamber-size and type specific (a standard type 30 is 2 inches, a long-stroke type 30 is 2.5 inches) and that the limit is stamped/marked, not guessed. Lining condemnation: less than 1/4 inch at the shoe center on air drum, less than 1/8 inch on air disc, plus cracks, contamination, loose rivets, or any lube on the friction surface. A wheel seal leaking onto a shoe is an automatic out-of-service, not a note-it item.
• Tires and wheels. Steer axle needs 4/32 minimum in a major groove; all other axles 2/32. No regrooved, recapped, or retreaded rubber on the steer axle of a truck or tractor. Mismatched duals: about 1/4 inch diameter difference max, and check for touching duals, exposed belts, sidewall cuts to the cord, and bulges. Wheel items: cracked or bent rims, elongated bolt holes, missing or loose fasteners, and welded repairs on a disc wheel.
• Steering and front end. Steering wheel lash measured at the rim by wheel diameter (about 2 inches on a 16 inch wheel, 2.5 on a 20 inch wheel - roughly 30 degrees on power steering). Kingpin vertical play limit around 1/8 inch. Any visible play in a tie-rod end, drag link, or pitman arm is a defect to repair, not to grease. Wheel bearing endplay in the 0.001 to 0.005 inch range, and know that a loose bearing shows up as lash you will mistake for steering wear.
• Cooling and engine-side PMI. Conventional coolant gets SCA/nitrite tested with strips (target roughly 3-5 units per gallon of SCA) to keep liners from pitting; extended-life OAT coolant is a different animal - you check freeze point with a refractometer and you use an extender, not SCAs, and you do not top it off with conventional. Air filter changes on restriction gauge (roughly 20-25 in H2O for a turbocharged engine), never on how dirty it looks. Belts with an automatic tensioner: read the wear indicator, do not measure deflection.
• The paperwork side. 49 CFR 396.17 periodic (annual) inspection, Appendix G criteria, 396.19 qualified inspector, 396.25 brake inspector qualification, and records retained 14 months. T8 asks who is allowed to sign the inspection, what has to be on the report, and what happens to a truck with a listed defect. This is free money and most techs skip it because it is not wrenching.

Where techs lose points on T8

Good technicians miss these — not from lack of skill, but because the question is built to catch them.

• Adjusting an automatic slack adjuster to bring stroke back in spec. This is the single most common wrong answer on the test. If an ASA lets the chamber run long stroke, the ASA (or the foundation brake) has failed and gets replaced. Manually cranking it hides the fault, and on the test that choice is always the bait.
• Grease it and go. Anywhere the scenario says 'visible play' in a steering or suspension joint, the answer is document and repair/replace before release. There is no mileage exemption, no 'watch it next PM,' and adjusting toe does not fix a worn tie-rod end. The plausible-sounding maintenance action is the wrong action.
• Mixing up the air numbers. 2 psi vs 3 psi is single vs combination; static vs applied changes it again. And a low-air warning that comes on at 55 psi is a failure even though it 'came on' - the requirement is 60 psi or above, not 'before the spring brakes drop.' They will build a question specifically on that gap.
• Reading tread depth as the only tire criterion. A steer tire at 5/32 still fails if it is a recap, if the sidewall is cut to the cord, or if it has a repaired puncture in the shoulder. Same on duals: legal tread and a 1/2 inch diameter mismatch is still a defect. Look for the disqualifier the question buried behind the depth number.

A study plan that works for T8

Roughly two weeks of real preparation, in the order that actually builds on itself.

1. Days 1-4: Frame and Chassis, because it is a third of the test. Build a one-page limits sheet - leak-down rates, governor settings, warning pressure, pushrod stroke by chamber, lining thickness, tread depth, kingpin play, wheel bearing endplay, fifth wheel gap - and rewrite it from memory each morning until it comes out clean.
2. Days 5-7: Engine Systems. Cooling chemistry (SCA/nitrite vs OAT, strips vs refractometer, liner pitting), air intake restriction, fuel filter and water separator, belts and tensioners, and aftertreatment PM items (DPF ash service interval, 32.5% DEF, DEF freeze at about -12 F, cracked DEF and pressure lines).
3. Day 8: Cab and Hood, Electrical, and Road Test in one pass. Lamps, mirrors, wipers, seat belts, latches, HVAC, gauges, horn, plus voltage-drop testing and load testing (half the CCA for 15 seconds, 9.6 V at 70 F). These sections are small and the questions are direct - do not overinvest, just do not leave them blank.
4. Days 9-10: Practice questions only, and read the two-technician items backwards - decide if A is right, then decide if B is right, then answer. Every one you miss, write the actual spec number on your limits sheet. If you can recite the sheet cold the night before, you are done studying.

Sample T8 questions

Straight from the bank — answers highlighted, with the explanation underneath.