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Driver Training
On another site a driver mentioned how he had a close call. He was of the opinion that if he had to make a hard stop he had to pump the brakes to keep them from overheating.
During the event he described it seems he had what might be called a panic stop, and he was at 70 MPH. He pumped the brakes and the end result was his air pressure dropped as a result and it dropped low enough so that his emergency brakes automatically deployed. When we first read the account of the close call it sounded like he had an air leak in his service brakes and that is why the pressure dropped and his emergency brakes were engaged.
But after a few posts it became clear this driver was of the opinion pumping his brakes would keep them from overheating.
I make this post to drive home the point that driving a vehicle with air brakes, such as our conversions, requires different techniques compared to driving our cars. If you are new to ownership of a coach and this is your first experience with air brakes please take the time to learn how to drive with air brakes, how to do pre-trip brake checks, and how to maintain and verify the safety features of the air brake system are functioning.
If you have any questions do not hesitate to ask. We want everybody to be safe.
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10 Replies
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The titile of this thread caught my attention.
If there was a Prevost driving school for potential new owners, I would be the first to sign up.
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I would be interested in a prevost driving School as well.
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I’m surprised Jon’s post didn’t get more than two responses and those were from members asking about coach training.
Jon makes an excellent point about a coach driver needs to understand the difference between hydraulic brakes on a passenger car and pickup/medium sized trucks VERSUS air brakes on a coach.
There are two reasons why hydraulic brakes on a passenger car/pickup lose effectiveness due to heat:
1. The pads/rotors and/or the shoes/drums get hot to the point where the braking action of the materials degrades. The magic temperature will be different for vehicle to vehicle due to the various materials that are used.
2. The brake fluid’s temperature at the brake caliper or drum piston gets to the point where it literally boils. Old brake fluid, dirty brake fluid, and brake fluid contaminated by moisture will have lower boilding points. Even a bubble or two of air will result in a soft pedal.
Both of these situations could happen if the driver rides the brakes down a long hill, especially if the vehicle is heavily loaded and/or pulling a trailer of any significance.
These situations can also happen when the driver is driving very aggressively on country roads with lots of curves and drives hard into each corner, braking hard, and racing into the subsequent corners. The driver might get a warning when he/she experiences a soft pedal going into a corner and then quits the agressive driving. But all too often there is little or no warning and the pedal goes to the floor and the driver panics and drives off the road headed for a large rock or a tree.
“Pumping the brakes” will sometimes bring back brake effectiveness. But if you get yourself in a situation where you have to pump the brakes, you’ve either (1) driven much too fast, too often into corners and/or (2) the brakes need immediate service.
Because the coach uses air to operate the brakes, we shouldn’t have to worry about “the fluid boiling”, but we do have to be worried about overheating the brakes on a long hill or series of hills. When the driver is faced with the long hill to go down and needs to maintain a reasonable speed, here are some things to consider incorporating into ones driving style:
1. starting out at a reasonable speed at the top of the hill (something less than 65 or 70mph) is how the descent should be started.
2. early and continuous use of the transmission retarder and/or the Jake brake during the descent. The driver needs to watch the trans temp when using the trans retarder.
3. If #1 and #2 don’t keep the speed at something the driver feels is safe and prudent, this is where the brakes should be applied, let the coach slow, and then release the pedal. Releasing the pedal versus riding the brakes will allow the brakes to cool. But the driver needs to watch the air pressure gauges to ensure that there is ample air in the system.
In my opinion, the brakes on a coach should be easily able to handle a panic stop from 70mph to full stop on a relatively level road without any material reduction in brake effectiveness. The brakes should get hot during this stop, but they shouldn’t get so hot that the pedal needs to be pumped.
I encourage other members to critic, comment on, challenge, or refute what I’ve written. This is how I drive our coach, understand how it works and should be operated, and if there is another school of thought … I want to be enlightened.
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I am planning a trip next month to Colorado next month and would appreciate comments on the best way to utilize the brakes on the down hill. Can I just drop it into 3rd and utilize the retarder? What is the best way to prevent the brakes form heating up?
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On a panic stop we have no choice and at that point the last thing I am going to be considering is overheating my brakes. In fact if it is a real emergency stop I am not sure there is enough time to think about hot brakes because all the concentration is likely going to be on hoping to avoid the impact.
But coming down a mountain is a whole different can of worms and the time to be dealing with overheated brakes is at the top of the mountain prior to the descent. As Dick said your speed as you begin downhill should be appropriate for the grade. Every downhill I have seen was makred in advance with both the length of the grade and the percent of slope. There is no reason to create problems for yourself if you plan and make use of all your assets. A jake or a retarder will both do an excellent job of controlling your speed, but if the grade is steep, when you are accelerating past your target speed, apply the brakes heavily and drop the speed 10 or more MPH below the target speed and then release them. Make sure your jake or retarder gets the benefit of high RPMs by being in the lowest gear possible for your target speed.
But with air brakes, never pump them unless you intentionaly are trying to deplete your brake system air pressure.
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When you need to use the brakes (last resort), use them hard over short distances to maximize the cooling between cycles.
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Bill, in Colorado, do not drive the bus on route 550 between Montrose and Durango. You can take your dingy and some extra underware.
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Every time you press your air brakes and release them, or pump them, that same amount of air pressure is exhausted out of your air tanks/lines etc. The compressor cannot keep up after repeated pumping. So, as long as your foot is pressing the brakes, that air will not be lost (unless you have a leak) until you release the brakes.
Most of us ole Truckers are used to a “Brake application guage” which shows how much air pressure you are applying to the brakes each time you press the brakes. I haven’t seen one of those in a Prevost.
Just trying to explain the mechanics of it, so some will undersstand why Jon and Dick are right!
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Having driven tour busses in and around Yellowstone National Park with MCI brand coaches, and ski and tour charters later in Colorado in Prevosts. Both instances, I was trained how to drive the mountains
Whatever gear you go up a hill,, you go down that hill in the same gear, or one lower using your “jakes brake or retarder.” Save your service brakes to slightly assist your “deceleration mechanism” and for emergency situation.
Here on I-70 in the mountains you will see truckers with their four way flashers on, going uphill and downhill about the same speed. Oh sure, here along the freeway in our western suburbs of Denver we do smell “odor of burning brakes”. Usually this, is created by a flatland truckers wanting to travel at automobile speeds down the hill. End result is overheated brakes. Several times a years local fire departments are called in for semi truck brake fires along I-70 on the west side of town
Remember, go up the hill in a gear your coach maintains, and go downhill in that same gear or a lower one you choose -
That’s good advice from Coloradobus. An effective engine brake (jake, exhaust, etc) will create about the same horsepower to slow the vehicle as the engine can create to move it. If your engine isn’t powerful enough to go up the hill in 4th gear, for instance, the engine brake won’t be powerful enough to maintain speed going down the same slope in 4th gear.
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