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What is the brakes fail?
I watched a video tonight on the Garage Journal Forum where an apparently loaded quad axle dump truck had its “brakes fail” (now, why, to what extent wasn’t mentioned), it hit a car waiting at a stop light, went the intersection, hit three more cars, and then carreened down a hit. Reports were that there were NO life threatening injuries.
If the brakes fail on a Prevost coach … i.e. push the brake pedal down and nothing happens at say 60mph … would the appropriate thing to do be to pull the parking brake? Wouldn’t that immediately lock up the drive axle? If that the right thing to do?
On a car/light truck with hydraulic brakes if the pedal went to the floor I would apply the “parking/emergency brake” by pressing on the pedal or pulling the Johnson bar.
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1 Reply
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I am not aware of any Prevost coaches that do not have spring brakes for parking or emergency. There might be some older vintage coaches, but of those listed in signature lines I don’t think the dump truck scenario would be what happens.
First it has to be understood that while air pressure is required for our service brakes to function, air pressure is also required to release our parking or spring brakes.
If there is a catastrophic and sudden loss of air pressure the emergency or parking brakes are going to automatically apply when the loss of air pressure drops our systems below abouty 45 PSI. On older coaches with a spring brake on the drive axle only the stopping force will be less than that on later coaches with spring brakes on the tag and drive axles, but unless the springs have broken all coaches with loss of air are going to stop.
One reason we stress every one should perform the pre trip brake test is to verify the parking brakes will automatically deploy as air pressure diminishes. If you have any question as to the condition of the springs in the parking brake put the coach in drive and see of the brakes hold or apply the parking brake at a very low speed to verify the coach will stop.
My 40 foot 1987 coach had a spring brake on the drive axle only. Spring brake meaning when the parking brake (emergency brake) was applied only the drive wheels were braked and that was by the large spring that is normally retracted when the brake is released. That parking brake was sufficient to hold my coach stopped on my driveway. But only barely. When a spring broke on one side my coach would no longer hold in the stopped position so I knew the brakes had an issue and I replaced the brake chambers. That is not part of the DOT pre trip brake inspection, but it was a clear indication my emergency braking would be compromised. The point is we as drivers have to be fully aware at all times of our coach and its systems because if we allow enough to go wrong and we defer maintenance we can end up like the dump truck. But if we do we have no one to blame but ourselves.
In our seminars and on this forum it may appear we are beating this DOT brake test requirement to death, but it is the only way you have to insure your bus is not in a video showing what happens when brakes cease to function. BTW long before your coach gets to the point where you have zero braking there are going to be so many clues such as lights and buzzers going off it is hard for anyone to reach the point where the coach is free wheeling.
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