310T Trailers

Question 1

During a pre-trip inspection, a truck driver checks the fifth-wheel locking mechanism. Which condition would require the vehicle to be placed out of service before moving?

Accepted Answer

The locking jaw does not fully engage around the kingpin and the release handle moves freely

Answer

If the locking jaw does not fully close around the kingpin and the release handle still moves freely, the trailer is not secured and could separate from the tractor — an immediately dangerous condition that requires the vehicle to be taken out of service. Grease on the plate is normal and required lubrication. A small amount of lateral play at the fifth wheel is acceptable and expected. The safety latch resting against the handle is its normal locked position.

Question 2

A trailer's tail lights work but the brake lights do not activate. The tractor's brake lights work correctly. Which 7-way trailer connector pin should a technician test first?

Accepted Answer

Pin 3 (Left turn / Stop)

Answer

On the standard SAE J560 7-way connector, Pin 3 carries the left turn/stop signal and Pin 4 carries the right turn/stop signal. Since tail lights (Pin 5 and 6) work but stop lights do not, the brake light signal circuit (Pins 3 and 4) is suspect. Pin 1 is ground — if it were faulty, tail lights would also fail. Pin 7 is reverse/auxiliary. Starting with Pins 3 and/or 4 targets the failed function directly.

Question 3

A technician is sliding a trailer's tandem axle group rearward. What is the PRIMARY reason a driver would want the tandem positioned fully rearward?

Accepted Answer

To shift weight rearward off the fifth wheel and reduce the drive axle load

Answer

Sliding the tandem rearward shifts load off the fifth wheel (and consequently off the tractor's drive axles) and places more weight on the trailer axles. Drivers do this to reduce drive-axle overloading. Sliding forward concentrates weight over the fifth wheel onto the drives. Stability is not improved by rearward tandem position (it can actually increase trailer sway). Kingpin-to-rear-axle distance regulations exist, but the primary operational reason for sliding rearward is axle-weight management.

Question 4

When inspecting a trailer kingpin, which measurement determines whether it must be replaced?

Accepted Answer

The diameter of the kingpin shank measured at its wear zone

Answer

Kingpin shank diameter is the critical wear measurement. Standards (such as CVSA) specify that a kingpin shank worn below a minimum diameter (typically 2 inches / 50.8 mm) must be replaced because excessive wear allows the fifth-wheel jaw to rock, creating coupling slop that can cause trailer separation. Height above and length below the plate are not wear measurements. Bolt torque ensures the kingpin is retained in the apron but does not measure kingpin condition.

Question 5

A trailer's spring-applied, air-released parking brakes release when the trailer supply line is pressurized, but one axle's brakes do not release fully. What is the MOST likely cause on that axle?

Accepted Answer

A seized or corroded spring brake chamber push rod

Answer

If the air supply is adequate (evidenced by other axles releasing fully), a spring brake chamber that does not release fully indicates a mechanical problem within that chamber — most commonly a seized push rod or corroded brake mechanism that prevents full spring compression. A leaking trailer brake valve would affect all trailer brakes. Low reservoir pressure would affect all axles equally. A failed glad-hand seal would reduce overall supply pressure, again affecting all brakes.

(310t) Truck and Coach Technician Certification Practice Test

(310t) Truck and Coach Technician Certification Practice Test

310T Trailers