[Larry]

I had almost the same experience in my old GMC 4104. It’s been several
years, maybe 20, but I still remember exactly what you describe. It is
breath taking, scary, it’s hard to express. I never had another panic
stop since. I’ve often wondered, is it normal for a bus not to slide the
tires under full pedal pressure?? Of course my old GMC had no ABS like
my 88 Prevost. I have had to get on the brakes very hard, but not full
pressure. I’m guessing it would not slide the tires under full pedal
pressure. I know the stopping distance is longer if the tires are
sliding. I would like to have enough braking force to do that if I
choose. Will the tires lock up on my 88 if I stand on the brake Pedal??
I guess I could do the test but I hate to flat spot my tires.

Ken

[Archived]

With the exception of early conversions almost all of our coaches produced since sometime in the 90’s have anti lock braking. Unless there is a fault, which should bring about the ABS warning light on the dash the system is working behind the scenes and we will never know when it is engaged.

In our cars the anti-lock braking is working on a hydraulic system. As it senses a wheel starting to slow faster than others the system releases braking pressure to that wheel(s) and then reapplies pressure as that wheel speed matches that of the other wheels. You can feel the application and release of hydraulic pressure as a pulsing or to use Hector’s term “chatter” because in hydraulics you cannot compress a liquid so what you feel is the banging coming from application and release of hydraulic pressure.

Our coach ABS works exactly the same. When the system senses a wheel(s) slowing at a greater rate than the others it relases air pressure to that wheel’s brake chamber until the wheel speed is equal to the others and then pressure is restored. If we could be at the valve controlled by the ABS “brain” we would realize it is chattering by alternately releasing and applying air pressure to the brake chamber but since the system is pneumatic we can not feel it because the air pressure is increasing and decreasing (like it does in our air bags) and the cushioning effect of air pressure masks the ABS system at work.

It is great Hector was able to stop. His video is a stark reminder of something everyone driving coaches needs to know and understand. At the 60 MPH Hector cites in the video our coaches will take over 300 feet to stop, more if you consider the distance traveled during reaction time, and the average car is going to be no greater than 130 feet, more likely 100 feet on some cars. If you are one of the drivers that likes to do the posted speed limit when it is 70 your stopping distance is well over 400 feet. The car in front of you can stop in 180 feet or less from the same speed.

ABS decreases stopping distances because a locked wheel has less braking effectiveness than a wheel with impending lockup. but none of us can alter the laws of physics so please understand that even with retarders, jakes, and ABS, our coaches and their braking systems cannot stop as quckly as the line of cars in front of Hector can.

[Archived]

Great heads up Hector… I assume you have some sort of dash cam like Jon?

[Archived]

This remark is made with tongue in cheek, but it is intended to keep us alert.

Had Hector hit the car in front his first action would have been to remove the card from the dash cam and flush it down the toilet.

Not kidding here……..I installed my dash cam because like everyone else I experience cars pulling in front of me far to close for the speeds involved taking away any safety zone for stopping I had. I would be defenseless without proof the car I just rear ended was in fact the cause of the accident. But I am very much aware now that my dash cam is on whenever my coach is running that cuts both ways and should I have a lapse in judgement and decide to tailgate it is going to no longer be my defense, but my undoing.

You know how you might be inclined to act differently when you know nobody is watching? Well, with a dash cam there is always someone watching.

[Archived]

Ken: Unless you’ve done a brake retrofit, I doubt that your 1988 has ABS. I’m pretty certain my earlier owned 1989 was not so equipped but I was never able to lock the drum brake equipped 1989 on dry roads with max pedal pressure.

[Archived]

Mine is a 97 and no ABS.

[Archived]

Tom,

I use a Go Pro 2, High Definition camera, mounted looking out the fronwindshieldld when I travel. I use the same camera on my RC airplane to record flights. It works great and it fun to review the days travel.

Hector

[Archived]

Tom????????

Are you sure no ABS?

[Archived]

No dash light, no blink code in the steering bay, no wheel sensors, no ABS!!!!!!

[William]

I work on automotive ABS systems very frequently and I know my 1988
Prevost does not have computer controlled ABS. It seems that it should
have been engineered with enough braking force to lock up the tires
under full pedal pressure. If not, I guess it does have anti-lock brakes
after all. I’m curious if the later model coaches have enough braking
force to lock up the tires if the ABS were disabled, all you folks maybe
like me and have anti-lock brakes even without computer control?? I
know it’s mostly about control on slick surfaces. I like ABS on slick
surfaces, but I’m pretty sure I can stop quicker on dry surfaces without
ABS, at least in the automotive world.

Ken

[John]

The mandate for ABS on commercial buses was 1999, however I know Prevost was installing ABS on coaches prior to that. Based on Tom’s response it was apparently an option because my 96 chassis had it.

I would be very interested in learning if we can lock up a wheel or axle. The problem with that however is all certification testing is done at maximum rated weights, which means an axle loaded less than its weight rating on a coach can be expected to lock prior to one at its maximum weight rating so to do an accurate test we would have to pretty well document the coach to insure air pressures are within spec, the axle weights are at maximum allowable limits and tire pressures are according to the manufacturer’s requirements for the axle weight.

Personally, while I know our braking systems are certified to DOT standards I would like to know with a good stab at the brake pedal I could “lock-em-up” something I have never been able to do with any coach.

[Larry & Diane]

Tom,

My coach is almost the same as yours and is only a few numbers apart on the Royale serial numbers. My coach has ABS so I’m assuming it was an option. I have never been able to lock up any of the wheels on self imposed tests to get an idea of just how fast the coach would stop. Jon is correct on the stopping distance being at least twice what it is on a typical car.

Hectors naration of the stop was great. It would be interesting to have one of the cameras that records the inside activity at the same time to see the expresions on the Hector and Lee’s faces.

[Archived]

I did some playing with pneumatic drawings last night and based on a drawing issued in 1993 Prevost offered ABS as an option at or around that time.

[Archived]

My 1991 H3-40 has ABS and disk brakes on the steer and tag axles. Even has a label on the engine hatch stating ABS Brakes. I have had to hard stop a couple of times mostly because I was not used to the 42,000 pounds of metal flying down the road. My Eagle Model 10 weighed in at 30,000 pounds and would stop much quicker than the Prevost. The Prevost was a smooth and straight stop though.

[Edward & Sandy]

Yes, you can stop coach tires at least with disc brakes.

Several years back, Chris and I were driving separate to make time from Palm Springs to Mira Loma with our then 2002 Marathon XLII single slide.

Following behind the coach in the car westbound, we were nearing the 215/15 interchange on I-10, when a sweet young thing decided to cut Chris off in the bus after she had past the exit’s lines. My viewpoint from behind, the rear of the bus went upwards, and billowing clouds of rubber smelling smoke hung in the air as I got to that spot. It was obvious to me from the rubber smelling smoke, tha some of the bus’s tires had stopped rotation during the panic situation. Glad we werent towing the Land Rover, no telling where it would have gone.