Wednesday, February 8, 2023


Test your motorhome air brakes—Here’s how

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?

David Hunt

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.

David Hunt

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.

David Hunt

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.

David Hunt

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 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!



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9 months ago

The picture of a tire pressure monitor when referring to air brake gauges kinda takes away the credibility of your article.

9 months ago

This is all part of the test to get a Non Commercial Class B or any of the Commercial drivers license in PA. Should be in every state in order to drive a rig with air brakes (Or any large rig or combo)

9 months ago
Reply to  Ike

You are correct in saying this for operators of motorhomes with air brakes in Penna and many other states. I do believe that Penna also requires a class B non commercial depending on weight of vehicle with or without air brakes A class A non commercial is required if towing 10,000 pounds or more. I live in Penna and drive a 40 foot pusher. If I got in an accident due to faulty brakes in a state that does not require a non commercial my insurance carrier may decide not to cover me. Simply know your state’s requirements.

9 months ago
Reply to  Ike

This ONLY applies to the air brake test. It does not apply to a class A or class B either non- commercial or commercial test. If your unit does not have air brakes, you will not take the “air brake test”. Also, you might want to ease ahead just a little before you get out to remove the wheel chock as you have probably put pressure against it when you released the “park brake”. The state of Pa. does not “require “you to have a commercial or a non-commercial license to operate a RV if you are not using it commercially for your own use. It should be noted that it would be highly advised to obtain a non-commercial license in the class of the RV you are operating though. In Pa. a non-commercial drivers license does not cost any more than a regular license. Now a commercial license is a different story . Both will require a knowledge and a skills test with appropriate vehicle. I gave the state of Pa. over 17 years as a qualified drivers license exaiminer (now retired!) certifing all classes

Jim Drmolka
9 months ago

120 pounds not 1200. If it went to 1200 lines would all blow apart.

RV Staff
9 months ago
Reply to  Jim Drmolka

Thanks, Jim. It’s been fixed. Have a great day. 😀 –Diane

Lance Craig
9 months ago

They are wheel “chocks” not “chalks”.

RV Staff
9 months ago
Reply to  Lance Craig

Dang! I know better! Totally missed that (obviously) when I proofed this last night. Thanks, Lance! Take care. 😀 –Diane

Gary Rightmire
9 months ago

The following statement is not correct: “ At 1,200 psi, the brake system governor will disengage,” I believe that the correct psi should be 120 psi.

RV Staff
9 months ago
Reply to  Gary Rightmire

Thanks, Gary! It’s been corrected. Take care. 😀 –Diane

Tom Moeller
9 months ago

This was an excellent article.In several blogs I belong to I’m amazed how many have no clue how important the leak down test is.Thank you for this fantastic article and I hope those with air brakes copy this so they get accustomed to learning the steps.

Bob p
9 months ago

I believe you have a serious typo in the article. I think you meant to say 120PSI not 1200 PSI.

RV Staff
9 months ago
Reply to  Bob p

Thank you, Bob. It’s been corrected. Have a great day. 😀 –Diane

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