What to do in case of an air brakes emergency?

[mrlupr]

So we went to visit my sister in Colorado springs this weekend and while driving up I25, I realized that there are a few hills that would put a toll on my bus especially as you enter Colorado from New Mexico. Driving south to North my biggest concern wasn't going uphill. My worry would be the very long downhill runs. Some of those downhill stretches went on for many miles. I could imagine that in the middle of summer with temperatures in the triple digits, the brakes on any vehicle would be put under a lot of stress.

My questions are:
1. Can I pull my parking brake if my air brakes fail?
2. Would pulling the parking brake eventually stop the bus or would it just lock up the wheels?
3. What should be my emergency protocol if I were to lose my brakes going down one of these steep hills?

If it helps, I believe the steepest grade sign I saw was a 6% downhill grade.

Our entire trip was Lubbock, Texas to Colorado springs, Colorado and we used Hwy87 through NM to I27 through southern CO.
I am planning on taking this same trip again as our maiden voyage during easter recess and dont want it to end like the Titanic.

I am trying to figure out what would be my game plan in the event of an emergency while manuvering up and down those hills.

We have a 2004 International CE200 10 window bus with a T444E, Allison 2000 and air brakes.

 

[Mountain Gnome]

1)if your air brakes loose pressure from a failure, the rear parking brakes automatically engage. If you park overnight (or maybe longer) and your air brakes (tanks) loose pressure, the parking brakes are engaged - you will have to have them up to about 60psi minimum to disengage them.


2)someone here said they tried that with an empty bus on an empty road as a test to see what would happen, and the rear end locked up. Maybe with a load they would just slow it down fast.


3)depends on your load (see #2). Last resort is an emergency run-away truck pullout that stops your vehicle. It just won't be a fun ride.


People will tell you not to ride your brakes, pulse them. That is a mis-understanding. The same amount of heat will be generated - it is a function of mass and gravity. They say let the pads cool a moment, then press, then cool, then press, but the pads do not pull away from the disks/drums more than the width of a sheet of paper - they don't get "air flow". They don't cool much between pulses. But the pulses can get hotter, cause you need to press harder, vs. pressing softly continuously. The same total amount of friction will be required to stop or slow or maintain-speed-of your mass.


The ONLY way to keep the pads/shoes from overheating is by going slower at the start, and keeping it slow. The same amount of friction will be generated, the same amount of heat will result from the friction, but it will be spread out over TIME which will allow it to induct throughout the brake drum and into the hub, spindle, axle, etc, as well as into the wind.


Also someone mentioned recently - never "pump" air brakes, because it depletes the air supply. You only need to "pump" hydraulic brakes when they spring a leak as you are driving, and the pedal gets soft and/or goes to the floor. Then "pumping" them can momentarily get more pressure to the pads, as they lost too much from the leak.

 

[Elliot Naess]

...

People will tell you not to ride your brakes, pulse them. That is a mis-understanding.

...

Source, please?

 

[Brad_SwiftFur]

1)if your air brakes loose pressure from a failure, the rear parking brakes automatically engage. If you park overnight (or maybe longer) and your air brakes (tanks) loose pressure, the parking brakes are engaged - you will have to have them up to about 60psi minimum to disengage them.


2)someone here said they tried that with an empty bus on an empty road as a test to see what would happen, and the rear end locked up. Maybe with a load they would just slow it down fast.


3)depends on your load (see #2). Last resort is an emergency run-away truck pullout that stops your vehicle. It just won't be a fun ride.


People will tell you not to ride your brakes, pulse them. That is a mis-understanding. The same amount of heat will be generated - it is a function of mass and gravity. They say let the pads cool a moment, then press, then cool, then press, but the pads do not pull away from the disks/drums more than the width of a sheet of paper - they don't get "air flow". They don't cool much between pulses. But the pulses can get hotter, cause you need to press harder, vs. pressing softly continuously. The same total amount of friction will be required to stop or slow or maintain-speed-of your mass.


The ONLY way to keep the pads/shoes from overheating is by going slower at the start, and keeping it slow. The same amount of friction will be generated, the same amount of heat will result from the friction, but it will be spread out over TIME which will allow it to induct throughout the brake drum and into the hub, spindle, axle, etc, as well as into the wind.


Also someone mentioned recently - never "pump" air brakes, because it depletes the air supply. You only need to "pump" hydraulic brakes when they spring a leak as you are driving, and the pedal gets soft and/or goes to the floor. Then "pumping" them can momentarily get more pressure to the pads, as they lost too much from the leak.

Sorry to disagree, but as a professional driver, and speaking from my own personal learning experience, you *WILL* overheat the brakes by riding them down a mountain, even at a low speed (yes, I learned this The Hard Way!) The correct way is to let the vehicle 'engine brake' and when it reaches max RPM, apply enough brakes to slow down 5-10 MPH, rinse and repeat. If you find yourself using the brakes excessively, then you are in too high of a gear, you need to gear down and slow down. This does in fact allow some time for the brakes to cool between uses.

An Old Timer once told me - you can do it a million times too slow, you can only do it once too fast.

 

[Johnny Mullet]

NEVER ride the brakes. Coast downhill and when the speed gets uncomfortable, hold the brake down and slow to a lower speed. Let it coast and repeat as needed. I been coast to coast with my bus and the worst decent was Flagstaff and had zero issues. I suspect you are gonna be fine!

 

[rossvtaylor]

Flagstaff...that's us!

I've got a CDL...which doesn't make me an expert, but it does mean that I've read the manual and I do try to stay current. I've also driven lots of different commercial rigs. The current standard, per the CDL manual, is that a driver should select a lower gear and downshift before starting down a hill. The gear should be low enough to allow the vehicle to coast, in gear, at your target speed. The manual also cautions against riding the brakes and, instead, says that if braking is needed you should apply the brakes to slow to 5 mph below your target speed...then let off the brakes. If your speed increases above the target, repeat as necessary. The book also cautions against shifting while going downhill (presumably a bigger issue for manual transmissions) because there is the danger that you might miss the downshift and be stuck coasting in neutral...which is both unsafe and illegal.

MrLupr - thanks for asking, because this is important info and good to learn. But this should serve as a caution to anyone buying a large vehicle...it's important to learn how it operates. How air brakes operate, what happens if you lose air pressure, the manner in which the spring brakes work, how to test your brakes, all of that...is covered in both the vehicle's manual and in the air brake endorsement test. Do you know where your slack adjusters are and how much movement is permitted? Do you know how spring brakes work? There are many things which aren't the same as in a regular car or truck. I'm not saying you need to get an air brake endorsement, but I strongly encourage you to look for some videos on CDL testing of air brakes. There are several things which an operator must do, and understand, in order to know their air brakes are working properly and how to use them.

Be safe and have (the good kind) adventurous travels!

EDIT to add a link to the Arizona CDL manual: https://apps.azdot.gov/files/mvd/mvd-forms-lib/40-7802.pdf

 

[bus-bro]

I would make sure the brakes are properly adjusted first. You probably have automatic slack-adjusters and you wouldn't normally need adjustment, but it would be of benefit to know what your slack is. Too much and you will need to use the emergency ramp.

 

[Sehnsucht-SKO]

Rule of thumb - whatever gear you went up the grade be in on most the same gear going down. Rely on the engine brake (or engine resistance if not a technical engine brake) to maintain and if still gaining speed apply enough controlled brake pressure to reduce speed 5-10 mph or whatever is just below your safe and comfortable descent speed. Release the brakes and they will have time to cool even as you gradually high up speed again. If you're gaining speed too quickly then you're in too high a gear.

As for air brake failure, yeah when they fail you'll know it. Air brakes are cylinders with powerful coil springs which apply brake pressure by default. When you build up air pressure and release the parking brake, you're sending air to those cylinders to counter those springs and force them to retract the brake pads. When you apply the brake pedal, you're simultaneously releasing the air which holds back the springs and asserting air on the other side of the valve to actually add air pressure that in addition to the springs will control how much brake is being applied. So when you lose air pressure by pumping the brakes or by a leak in the system, you're inviting a low air pressure situation that will eventually drop below the limit of 60psi at which point the parking valve will pop and the springs will clamp down on those brakes which will lock you up and probably spin you out. Not the situation you want to be in if you were already fighting for control downhill. You will be getting a low air warning light and buzzer no doubt before you reach that point but that's not the time to be figuring out how close to the limit you can get.

Air brakes aren't harder to use but do require a little bit of attentiveness in how you're using them. Plenty of us here drive them daily and many of us even in steep terrain and poor weather so please PLEASE ask anything you don't understand or are unsure because none of us want to see you in a ditch or over the side of a mountain!

 

[Ronnie-SKO]

When Johnny says coast that does NOT mean put it in neutral and actually coast. He means in gear foot off gas.

 

[BeNimble]

You might carry an anchor with a short chain..works for boats.
A big one would work.

 

[Elliot Naess]

Time for a little friendly thread drift, indeed.
Stand by for justice!

 

[rossvtaylor]

To clarify the system pressure numbers for you...in a properly configured and operating system (part of why you need to do the air brake checks) you'll get a warning when the pressure in the system drops below about 60 psi. This should be an audible buzzer and a warning light. In our old Gillig, we also have a cool red arm (a lollipop) that drops down in front of us...but that's pretty old school. Anyway, you should get a low-pressure warning at about 60 psi and the spring brakes won't normally come on fully until the pressure drops to about 20 psi (at which point the yellow parking brake button will pop out). So, you have a bit of notice if your air is dropping, from the time you get the alert until the rear spring brakes come on. Depending upon the leak rate, that may be pretty brief. The point is that, if you get a low pressure warning, you should move to the side of the road and stop as soon as it's safe to do so. Once those spring brakes come on, there's no moving the bus without airing up the system again. (Note...some buses, usually transit types, have an emergency air tank which can be used to release the spring brakes briefly so the bus can be moved off the roadway)

 

[mrlupr]

I want to thank everyone for all this amazing and useful information. I see I still have a lot of homework left ahead of me.

I also decided to study up to get my air brake endorsement. I think in doing so I'll feel more sure about myself.

 

[Mountain Gnome]

Sorry to disagree, but as a professional driver, and speaking from my own personal learning experience, you *WILL* overheat the brakes by riding them down a mountain, even at a low speed (yes, I learned this The Hard Way!) The correct way is to let the vehicle 'engine brake' and when it reaches max RPM, apply enough brakes to slow down 5-10 MPH, rinse and repeat. If you find yourself using the brakes excessively, then you are in too high of a gear, you need to gear down and slow down. This does in fact allow some time for the brakes to cool between uses.

An Old Timer once told me - you can do it a million times too slow, you can only do it once too fast.

No, thank you for disagreeing. That is what makes this a better place. No one here has all the answers, and I am not a pro-driver with that experience.



What if you don't have an engine brake, like me with an AT545? No lockup converter, no can downshift.


Then you said it at the end....my whole point: go slow.



I overheated my brakes in downtown Atl trying to beat stoplights, and then jamming them quick and hard at the last sec to avoid running the red. In a little empty 1983 Toyota pickup. After 4 successive lights, they started fading. By the 6th, I was having trouble stopping. Was pressing them less time than not pressing them. In fact, I was stopped at the light for a minute. But the TOTAL amount of time was shortened, because I was jackrabbit "racing" between lights (were close together). And the intense heat of jamming them did not have time to dissipate. It overheated the surface of the pads.





Not trying to bash you, but if you overheated going downhill, you were going too fast with too much of a load, methinks.

The current standard, per the CDL manual, is that a driver should select a lower gear and downshift before starting down a hill. The gear should be low enough to allow the vehicle to coast, in gear, at your target speed. The manual also cautions against riding the brakes and, instead, says that if braking is needed you should apply the brakes to slow to 5 mph below your target speed...then let off the brakes. If your speed increases above the target, repeat as necessary. The book also cautions against shifting while going downhill (presumably a bigger issue for manual transmissions) because there is the danger that you might miss the downshift and be stuck coasting in neutral...which is both unsafe and illegal.

This ^^^ relates to what I am saying. Slow down in the first place - 5MPH below target speed (a.k.a. "truck" speed limit). Then if/when you speed up, apply until slower. Not "pulse" until slower. On the steepest of hills, that target speed should be way low. With no lockup and no ability to downshift, go slower!


IDK, they said when I was in school I was smart...kids cheated off me. I never "felt" that way, but physics was so simple to me, I was skipping 32% of the days (max # I could without failing), smoking buds, rebelling like a teen, but I still made "A"s in those classes. And from what I remember, the total amount of heat generated is a factor of mass and gravity. A set amount of heat-generating friction is required to balance the force of gravity - no more - no less - to maintain speed downhill (remember, some friction comes from the wind-resistance, also), doesn't matter how fast that speed is maintained. But then there is inertia also, and if you are going fast in the first place, gotta overcome that to slow down. Pulsing the brakes concentrates that friction in a limited amount of time. Gotta spread out the time....go slower....

 

[Brad_SwiftFur]

...
Not trying to bash you, but if you overheated going downhill, you were going too fast with too much of a load, methinks.
...

I am not ashamed to admit this was Way Back When, early in my driving career, and before (or should I say, when) I Learned Better. I did not have a skilled instructor by my side to mentor me, I fortunately had enough knowledge to realize when the brakes were beginning to fade, brought the truck to a stop and finished the descent at 3 MPH in 1st gear.
I was driving a '73 Cabover Pete with a "318 Detroit", 13 speed, 4.11 gears and "Armstrong Steering" (no power steering), and this ol' truck didn't have brakes on the steering axle (came from the factory that way).
This incident could have gone downhill in a Big Hurry (Pun Intended) but I am fortunate to have learned from it instead of it ended tragically.

 

[Oscar1]

Sorry to disagree, but as a professional driver, and speaking from my own personal learning experience, you *WILL* overheat the brakes by riding them down a mountain, even at a low speed (yes, I learned this The Hard Way!) The correct way is to let the vehicle 'engine brake' and when it reaches max RPM, apply enough brakes to slow down 5-10 MPH, rinse and repeat. If you find yourself using the brakes excessively, then you are in too high of a gear, you need to gear down and slow down. This does in fact allow some time for the brakes to cool between uses.

An Old Timer once told me - you can do it a million times too slow, you can only do it once too fast.

This is what you do!! As both Brad and Johnny said you don't ride the brakes, you use and aggressive brake application to slow down then release and do it again. Slow down at the top of the hill before starting down and keep it slow that way. You'll do fine and if you want take an air brake endorsement course to feel more confident, not expensive and money well spent.
Cheers

 

[Mountain Gnome]

When I visited my bro in Jackson Hole, WY, they told me of a tow truck that picked up a Cadillac up near the top of the pass, wife of some rich rich rich well-known guy in town with a big spread and mansion. New tow-truck driver. Headed downhill (very steep) in high-gear at high-speed, riding his brakes, until they overheated, he couldn't stop, and he came roaring into town and flipped in the curve, with the old lady and her dog inside. I heard the dog survived.


SLOW. (and avoid that pass in your bus with an AT545)



To put it another way, if you're braking/slowing to 5MPH below target speed, then letting off and speeding up, and doing it again and again, and that repeat is so fast that you are "pulsing" the brakes, then the force of gravity is too much - the hill is too steep - to go fast. At some point the hill will be so steep that the "on" cycle will be required to be more than 50% to maintain speed, and eventually (not a likely existing legal, drivable paved road - i.e. >30% grade [?] or something) will require you to hold the brake on continuously, or you will speed up uncontrollably. At some point, the hill will be so steep that your brakes won't stop you (like >50% grade - again imaginary).


With my AT545, I speed up on any downhill stretch. Some hills I gotta hold the brake more than not, or I speed up. Those are the ones to go slower! If your brake "on/off" cycle gets to the point of "pulses" (50%/50% - 100%/0%), you gotta slow down and let TIME dissipate the heat. I might ride the brakes downhill, but slowly. The harder you have to press, whether holding or "cycling/pulsing", the slower you need to go.


That's what I think. No source but my bowl of wet noodles that have been fermenting for 50 years.

 

[Oscar1]

No, thank you for disagreeing. That is what makes this a better place. No one here has all the answers, and I am not a pro-driver with that experience.



What if you don't have an engine brake, like me with an AT545? No lockup converter, no can downshift.


Then you said it at the end....my whole point: go slow.



I overheated my brakes in downtown Atl trying to beat stoplights, and then jamming them quick and hard at the last sec to avoid running the red. In a little empty 1983 Toyota pickup. After 4 successive lights, they started fading. By the 6th, I was having trouble stopping. Was pressing them less time than not pressing them. In fact, I was stopped at the light for a minute. But the TOTAL amount of time was shortened, because I was jackrabbit "racing" between lights (were close together). And the intense heat of jamming them did not have time to dissipate. It overheated the surface of the pads.





Not trying to bash you, but if you overheated going downhill, you were going too fast with too much of a load, methinks.






This ^^^ relates to what I am saying. Slow down in the first place - 5MPH below target speed (a.k.a. "truck" speed limit). Then if/when you speed up, apply until slower. Not "pulse" until slower. On the steepest of hills, that target speed should be way low. With no lockup and no ability to downshift, go slower!


IDK, they said when I was in school I was smart...kids cheated off me. I never "felt" that way, but physics was so simple to me, I was skipping 32% of the days (max # I could without failing), smoking buds, rebelling like a teen, but I still made "A"s in those classes. And from what I remember, the total amount of heat generated is a factor of mass and gravity. A set amount of heat-generating friction is required to balance the force of gravity - no more - no less - to maintain speed downhill (remember, some friction comes from the wind-resistance, also), doesn't matter how fast that speed is maintained. But then there is inertia also, and if you are going fast in the first place, gotta overcome that to slow down. Pulsing the brakes concentrates that friction in a limited amount of time. Gotta spread out the time....go slower....

Hello Gnome

You're right no one here has all the answers but Brad and Johnny have the right one for this question. As you said I'm sure you're a smart guy but you are not a commercial driver so it's not really a debate type question. Otherwise every driving school in North America must have it wrong. And it really doesn't matter if you have the AT545 or not the only thing that matters is start slow and stay slow, the way to stay slow is a low gear and short aggressive brake applications to keep your speed and rpm's down. If you started down that hill in too high of a gear you better figure it out fast.
Cheers
Stay safe out there

Oscar

 

[Sehnsucht-SKO]

To clarify the system pressure numbers for you...in a properly configured and operating system (part of why you need to do the air brake checks) you'll get a warning when the pressure in the system drops below about 60 psi. This should be an audible buzzer and a warning light.

Correct and thanks for the correction. I think I said this incorrectly in my post - the warning should begin at 60psi but the brakes won't lockup until 20psi.

 

[Ronnie-SKO]

I have to say I do not understand why it is said you can not downshift an AT 545. It shows on the gear shift lower gears will it not allow a lower gear even though they are shown on the gear shift?


My 89 Dodge with a cummins had the 727 automatic. Three speed, no lockup converter. Great trans could take anything that engine put out, and I had it turned up pretty good. Long mountain grades I would drop it in 2nd and it would hold back nicely with heavy trailers in tow. The torque converter does not freewheel, as long as you are above stall speed.


So it would seem to me that with the 545 you should be able to do the same.


With the 545 are you going up in high gear or has it downshifted? if it has downshifted to go up the hill/mountain then select that same gear it downshifted to for coming back down the hill/mountain.