The drain valve on a dolly's air tank must be closed so the tank holds the air the dolly brakes need. During the same walkaround, the shut-off valves should be open at the rear of the front trailers and closed at the rear of the last one.
The dolly's air tank drain valves must be shut, or the tank will leak the air its brakes depend on. The pintle hook must be latched so the dolly's eye cannot slip out and let a trailer break away.
Each added trailer brings more critical parts, such as a converter dolly, pintle hook, air and electrical lines, and shut-off valves, and all of them must be checked. The cargo and the way the trailers are built are not what makes the difference.
Air hissing out of the valve at the back confirms that service air is reaching every trailer. If no air comes out, make sure the shut-off valves on the other trailers and dollies are open, because air must reach the back for all the brakes to work.
Air rushing out at the very end of the rig, first from the emergency line and then from the service line, proves both lines carry air through every trailer and dolly. If you hear nothing, make sure the shut-off valves on the trailers and dollies ahead are open.
For travel, each landing gear must be cranked all the way up and must not be bent or damaged, so both conditions have to be confirmed. A gear left partly down or with bent parts is a defect to be fixed.
The pintle hook is what connects the dolly to the trailer ahead, so the eye must be fully seated and the latch closed; otherwise the dolly could come loose.
A pintle hook connects each converter dolly to the trailer in front of it, so the eye has to sit fully in the hook and the hook must be latched; otherwise a trailer may come loose on the road. Both the shut-off valves on the rear of the last trailer and the drain valve on the dolly's air tank should be shut, not open.
Closing the rear valves on the last trailer keeps air from venting out the back, while the valves on the trailers ahead must be open so air can pass through to the end of the combination.
Dollies equipped with antilock brakes must have an ABS malfunction lamp, and that lamp is yellow and mounted on the left side. It warns you when there is a problem with the antilock system.
ABS is required on any converter dolly built on or after March 1, 1998. A dolly that has ABS shows a yellow lamp mounted on its left side, so a quick walk-around look tells you.
When that valve at the very end of the rig is opened, air should rush out, proving the supply line is charged through every trailer. If nothing comes out, check that the shut-off valves along the way are open, because without air all the way back the rear brakes will not work.
Air-braked trailers and converter dollies manufactured on or after March 1, 1998 must have ABS. Air-braked truck tractors were covered a year earlier, starting March 1, 1997.
After the standard combination-vehicle checks, verify that the shut-off valves at the back of every trailer are open, except on the last trailer, where they must be closed. Also inspect each converter dolly and confirm that air reaches the brakes on all trailers.
Under the roadside out-of-service criteria (the North American Standard), a converter dolly riding between the trailers of a standard double is not taken out of service just because its stop lamps or tail lamps are missing.
Every question in this set has its own page with the correct answer and an explanation.
