CDL Air Brakes case studies
CDL Air Brakes · Put your knowledge to work in context.
The CDL air brakes knowledge test is the written exam a commercial driver takes to be certified to operate a vehicle equipped with air brakes. Passing it - along with the required vehicle inspection demonstration - is what allows the "No Air Brakes" restriction (an L code or similar, depending on the state) to be removed from a commercial learner's permit or license. Without that removal, you may still hold a CDL, but you cannot legally drive trucks or buses whose service and parking brakes operate on compressed air. The exam is aimed at drivers moving into heavy straight trucks, tractor-trailers, dump trucks, transit and school buses, and any other air-braked vehicle. The CDL Air Brakes case studies are 5 cases and about 3,156 words.
1The Slow Build: Compressor, Governor, or Air Dryer?
You are assigned a 2018 tandem-axle tractor pulling a loaded 53-foot van, about 76,000 lb gross, on a cold morning. At fast idle (1,200 rpm) with both gauges reading 85 psi, pressure takes 90 seconds to reach 100 psi; the standard is 45 seconds or less.
543 words, about 3 min2Primary Circuit Failure at Highway Speed
You are driving a loaded tractor-trailer on a two-lane highway at 55 mph. Without warning you hear a loud rush of escaping air.
712 words, about 4 min3Leak Test and Pushrod Stroke on the Same Pre-Trip
Before departure you run the air brake tests on a tractor-trailer. With the system charged to 118 psi, engine off and brakes released, pressure falls to 113 psi after one minute - a 5 psi drop.
519 words, about 3 min4Six Miles of 7% Grade
You are at the top of a six-mile 7% downgrade in a 78,000-lb tractor-trailer with a 10-speed manual and an engine retarder. The posted limit for trucks is 40 mph.
693 words, about 3 min5Water Crossing, Then a Grade at Shutdown
You cross a flooded dip with about 18 inches of water. A mile later, at 40 mph, the truck pulls right and takes noticeably longer to stop.
689 words, about 3 min