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THIS IS IMPORTANT
Until our coaches lean, or our auxiliary compressor starts running too much few of us pay much attention to the air systems in our coach.
When a coach is relatively new we all can get away with ignoring the needs of the coach’s pneumatic systems………..for a while. If you are one of the owners who hasn’t given your air system much thought this is directed at you.
Today, right now, get in the driver’s seat of your coach and do a pre-trip brake check. Don’t put it off. Don’t tell yourself you will do it later. Take five minutes and do it now. It is that important, especially if your coach has some age on it.
I’ll save you some time and tell you the steps so you do not have to google them. First air up the coach and chock the wheels so it will not roll. Turn off the engine. Then release the emergency or parking brake. You should see the air pressure needle on the primary gauge wiggle and go down a little. Then it should stay at that pressure without dropping. A few pounds of pressure loss per minute is allowed, but let’s be realistic. There should be no leaks.
After verifying the parking brake system has no leaks, apply the service brakes. For those of you from E. TN that means step on the brake pedal. Do not release the brake pedal, but observe the needles on each pressure gauge. They will wiggle a little and go down a few pounds pressure, and then if the system is leak free there will be no further pressure drop. A pressure loss of a few pounds per minute is acceptable, but again, there should be no leaks.
Turn the key on, but do not start the coach engine. Fan the brakes and watch the gauges as the pressure drops on both the primary and secondary brake systems. When the pressure drops to 60 or 70 PSI (I’m allowing for gauge errors here) a red brake pressure warning light should come on for each system as they reach that pressure and the lights should be accompanied with an audible alarm. (for those of you from Waleska GA fanning the brakes is rapidly applying and releasing them which releases air with each application)
Continue fanning the brakes. At around 40 or 45 PSI the emergency brake should apply itself. Note the pressure at which that happens. At that point you can start the coach and verify the engine driven air compressor is working by noting the air pressure rises quickly from a low pressure up to a safe working pressure of 90 PSI or above.
That completes the pre trip brake check and it is something you should do prior to every trip. A few minutes of work doing this check will verify your brakes are good, or will provide an early indication something needs attention.
Our air system is much more than just brakes, but nothing else is as important. To keep the system in good shape we all need to insure that we keep it dry by draining the air tanks to zero every time the coach is serviced, keeping the dryer and its cartridge or element is in good condition, and by chasing leaks as they are noted.
How many of you have done a brake check and found a problem? How many of you have never done a brake check? When is the last time your air tanks have been drained, and doing that how many of you have verified the operation of the check and protection valves? When was the last time your air dryer was serviced? Inquiring minds want to know.
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13 Replies
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Jon, no joke, I read this post, grabbed my laptop, told the kids “I’ll
be right back” and drove out to the bus. I ran the break test and it did
just what you said it would do. It passed. Honestly, it had been a while since
I’ve done one but no more. I think I’ll reduce your post into a step by step
“pre flight” check list laminate it and keep it in the front
drawer by the drivers seat and I will incorporate it into my walk around each
time before I drive.Thank you!
Fred
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That’s good news Fred. I hope nobody finds a problem with the brake system. But I know from first hand experience that if a hose is chafing, or a brake chamber diaphragm is starting to leak that minor problem can get real bad, real fast. And while a brake check is only a small part of a pre-trip inspection it is a very important portion of it.
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Great reminder of this very important
pre-trip inspection. Let’s face it, stopping 50K lbs of bus in an
emergency situation absolutely demands that everything is working
properly, your life may depend on it. -
On our return trip from our summer travels to Michigan, I was driving on I 57, heading south to Texas. What a pleasant drive……. until I noticed my primary and secondary air pressure cycling. The Bendix air compressor would build pressure, then I could see the pressure decreasing to the point of the compressor engaging again. This cycle would take about three – four minutes. Yikes, I had a leak!!
I pulled into a Walmart in Skiteston, Mo to check things out. When I engaged (released the parking brake chambers, thus engaging the parking brake) the parking brake, the air leak stopped. Humm… I self diagnosed the issue as a leak in one of my parking brake chambers, or a supply hose to the same. After working the issue, it was determined that the parking brake supply hose to the left rear parking brake assemblies had an air leak. The hose had failed and was leaking air, big time.
I was fortunate that I was able to have the hose replaced by a truck repair facility and continued on our trip with only a minor delay. However, the mechanics stated the normal occurrence of this type of failure is either the parking brake engages and the vehicle is disabled on the highway, or the parking brake engages partially and the wheel begins to heat up, with a fire or heat related damage as the result.
I am not one to check out my brakes before departure, but definitely a safe thing to do. I definitely agree with Jon that a little pre trip planning can avoid a vehicle being disabled or worst, a fire. It is so easy to release the parking brake and listen for any air leaks before starting the coach before a trip.
This winter, I will replace all the rubber brake hoses under the coach in hopes of avoiding this issue in the future.
Good Luck.
Hector
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Just to add to this, many moons ago I was heading from FL to NY state. After about an hour I noticed one of my air pressure gauges was cycling up and down. It was raining and I had air wipers on the bus so I attributed the cycling to the fact wipers were using air. But when I turned off the wipers the cycling continued. I ignored the clue that was staring me in the face.
When we hit Charlotte rush hour traffic and I was at idle speeds and using the brakes I noticed real quick the compressor was no longer keeping up with the air loss and I was fortunate to be able to get off the highway to a wide safe spot. What started out as a small leak causing my pressure loss and constant cycling of the air compressor was a failed diaphragm in the drive axle emergency brake chamber. and the small leak took a few hundred miles to turn into an unmanageable leak that shut me down. Just as I got off the highway into the safe spot the red light and buzzer showed me how important they were. Just as I got almost stopped my emergency brake popped on because the pressure had dropped that low.
My point is even if everything checks out and we get underway, our gauges will help us learn of issues if we choose to pay attention. I have carried that lesson for a long time and I should have known better.
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On the same subject, air leaks, that is one reason I insist on
having an aux air pressure gauge on or under the dash. You can easily
catch suspension or other leaks by watching how often the compressor
cycles. Without that gauge, you could have a serious leak causing
the compressor to run constantly trying to keep up and never know
it.If you have a brake leak, you can catch it with the primary and
secondary brake air pressure gauge as mentioned in the other posts
and with an aux gauge, you can do the same thing. A
really bad aux leak like an air bag or hose won’t have any effect on
your brake tank air until you use the brakes,
deplete the air because the compressor can’t keep up and the next
thing you know the buzzer/lights come on, your out of air and the
emergency brake is about to shut you down. All of that could be
avoided if you knew you had a bad aux leak and could get off the road
safely.Note – The aux gauge will show the compressor cycling as a normal
function since the suspension is using air as your driving. If you
get used to watching that gauge, you can catch what is not normal and
know you have a leak. -
Hmmm,
I never leave my aux compressor on when driving. I didn’t with my last plastic coach either. Am I missing something or shouldn’t the main engine compressor be adequate to support all air needs? As stated previously, passenger buses don’t even have aux compressors.
My main, secondary, and aux pressure routinely varies from just over 100 psi to 115 psi. I assume this range to be normal. Should the range be different?
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In British Columbia it is now manditory to have an Endorsement “Vehicles with Air Brakes” on your Drivers Licence in order to legally drive any vehicle with air brakes. To get the endorsement you must take a 2 day course on “Air Systems”. It covers the integration of all the air systems in a vehicle.
Jon’s description is exactly what is required prior to any road trip. One additional recommendation is to drive the vehicle forward a number of feet and apply hard braking to insure the brakes hold and do not pull to one side or the other.
This course had us crawling under semi trucks to adjust the “manual slack adjusters”. Fun thing to do on a cold wet rainy day!!! Thank goodness for “automatic slack adjusters” on coaches.
One other item to take note of, in British Columbia (and probably many other places) at every “brake check pull out” on our mountain roads there are large signage maps of what to expect on the down hill highway that awaits you. The map shows each curve and the recommended speed for each curve all the way to the bottom of the hill. Sure provides for some planning and reduces the suprises that lay ahead.
Jim
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Gil,
Your question about the aux compressor is a good one. Typically aux compressors have cut in and cut out pressures much lower than the coach aux system. Note that we not only need primary and secondary air, it is critical we have aux air because our suspension, belt tensioners, transmission retarder, and some other bus systems rely on aux air.
But when we stop some of us also need aux air for house needs or for slide seal inflation. I don’t think Tom was suggesting we need our aux comressors on necessarily although even if turned on they are likely to not operate, but was suggesting all of our air pressure gauges tell us important information.
Not all of our coaches have aux air pressure displayed, but when it is displayed it is another way to verify the health of our air system which is vital for our coaches.
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I did not suggest to run the aux compressor while driving, if it came out that way, sorry Gil. As a side note, I have my aux compressor set at 60/90 so even if I left it on, it would not cycle.
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Jon,
Good Information. I tested Mine today , And it passed ! This is on the Pre-Flight List !
Thanks,
Rocky
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Jon,
Last week I had the steer wheels removed to check brakes, lubricate, and generally clean the front end of the bus. Brake inspection revealed that both rotors had tiny, hairline cracks on both surfaces (inside and out) that pretty much covered the surface of the rotor exposed to the brake pads. There were no breaks or groves and the surfaces were smooth and shiny. I assume that the cracks result from heat checking and I am wondering if the presence of heat checking to any degree is cause for replacing a rotor. Or, is some heat checking acceptable and if so how much?
I recall that on another forum you posted instructions on how to perform a DOT brake test but I can’t find it. Is the Dot test the same as you describe at the beginning of this post?
Best Regards,
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I had heat checking on both disks and drums. I never viewed them as cause to replace either, but I am not an expert. If I saw a crack in the disk or drum that would be a definite cause to replace them.
The brake check procedure I listed above is a less detailed version of the process described in a typical commercial driver test manual. The actual and correct procedure gives specific values for acceptable pressure loss over a one minute period. It also defines an acceptable time span for pressure rise at the end of the test to determine the acceptability of the compressor output. If you stop at any commercial driver test web site or test facility you can access the correct and complete procedure.
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