When Fred Flintstone brought his Stone Age car to a stop, it frequently resulted in road-rashed feet. If Fred had taken up RVing, one can only imagine the frequent visits to Bedrock’s podiatrist. Fred put his feet to the test. The question is, do you put your air brakes to the test—every travel day?
Engine off—leak down test
If commercial truck statistics bear any relationship to motorhomes, then the importance is an easy call. A federal government study showed brake failure was involved in 29.4 percent of all truck crashes. Making sure your brakes actually brake is critical. How do you do it?
Testing your rig’s air brake system is easy, and takes only a few minutes. Because of how critical brakes are for your—and everyone else’s— safety, an air brake test is best done at the start of every driving day.
Chock the drive wheels of your rig.
With the engine off, turn the key far enough on to activate your gauges. Don’t turn the engine on.
Release the parking brake. For most, that means pushing the yellow knob IN. At this point, you’ll likely hear a hissing noise. Keep your eye on the gauge(s) indicating your brake system pressure. When the pressure stabilizes, use a timer to count down one minute. The pressure should NOT go down more than 2 psi over that minute.
Now put pressure on the service brake (your brake pedal), holding it down. Hold the pedal down for a timed one-minute interval, while watching the brake system pressure gauges. The pressure should not go down more than 3 psi over the minute.
Now pump (or “fan”) the service brake pedal and watch the air pressure gauge(s). At some point between 50 and 60 psi, you should see and hearing warning indicators, advising you of a “low air” situation.
Keep pumping the service brake until the parking brake comes on. You’ll know it when the parking brake knob pops out, away from the dash. This should happen when air pressure drops to somewhere between 40 and 20 psi.
If your system doesn’t work as indicated above, you need to call an air brake certified mechanic for help.
Engine on—leak down test
Start the engine.
Hold the throttle so the engine stays at 1,300 to 1,500 RPM. Brake system air pressure should build to around 60 psi, at which point the “low air” warning system should switch off. At 120 psi, the brake system governor will disengage, causing the brake system compressor to shut down.
Rapidly fan the service brakes, and as the pressure goes down, the governor should call for the compressor to start up again.
Now remove the wheel chocks (ensure the parking brake is set!)
With the parking brake applied, shift the transmission into a low forward gear. The parking brake should hold your rig, not allowing it to creep forward.
Release the parking brake and pull forward at 5 mph. While keeping your hands on the steering wheel, step on the service brake. Note if there’s any “lagging” on the part of the brakes, or if your steering wheel pulls. Neither should happen. Instead, your coach should come to a complete, smooth stop.
A daily air brake test ensures your system is “up to snuff” and will be ready to keep you, and others, safe on the road. Poor Fred. He had to wait until 1869 when a man named George Westinghouse invented the modern air brake system. Fred’s feet could have used the brake!
Note from editor: Our thanks to Joe Bulger, a longtime RVtravel.com reader and frequent commenter, who suggested in the Comments section that we run a piece on how to test an RV’s air brake system. Here ya’ go, Joe! Great idea!