With slippery road conditions in winter time, comes the problem of controlling tandem axle fire apparatus. Unless your department’s tandem axle apparatus are equipped with ABS sensors on each of the drive axles, it is still possible to get a lock up condition which could put the apparatus into a skid causing the driver to over re-act and apply the service brakes making the condition even worse. Understanding how the ABS works on a tandem axle vehicle is very important to the vehicle’s safe operation.
Most tandem axle trucks, including fire apparatus, have ABS sensors on only one of the rear axles. If the driver engages the retarding device on the truck to slow the vehicle without the use of the service brakes, the driving wheel (yes, the single driving wheel) could lock up and put the apparatus out of control unless that axle has ABS sensors on it. Power from the engine always goes to the wheel with the least amount of traction because it is easier to turn. By the same degree the engine’s braking force will always go to the wheel with the least amount of traction because it is easier to slow. If that wheel is on an axle without the ABS sensors it will either spin in a power situation or lock up in a retarding situation. By engaging the inter-axle lockers (not the differential lockers) the wheel on the axle without an ABS sensor is now mechanically connected to the opposite wheel on the axle that does have an ABS sensor and is now prevented from locking up because the ABS system automatically disables the retarder until all wheels are turning at the same speed again.
Any time that road conditions are less than favourable (dry pavement) always engage the inter-axle locker on a tandem or triple axle truck to prevent wheel spin or lock up. Engaging the inter-axle lockers also splits the load for one wheel to slow down or power up by one half thereby making it easier for the tires that are slowing or pulling the weight of the apparatus to do the job.
Have you ever thought of where you are holding your hands on the steering wheel while driving? Where would your hands end up if you were involved in a collision and they were at the top or crossed over to the other side of the steering wheel? That’s right! In your face! And when you consider that air bags in steering columns deploy at several hundred miles an hour, which is why so many people injure themselves when involved in a collision.
Place your hands at the eight o’clock and four o’clock positions on the steering wheel and shuffle steer. It may take a bit of concentration to begin with but you will be surprised at the results. You will be able to drive longer distances and still have better control of your vehicle if you have to make an evasive manoeuvre. Your arms won’t tire from holding them at the top of the steering wheel or even the 10 and 2 position which some of us learned years ago. Not only that, if your vehicle starts into a slide at highway speeds, it helps to lessen the chance of ending up in a ditch or median or ever worse in a collision with another vehicle. Ever watch car racing on TV? That’s how race car drivers drive so that they have the utmost control of their race car.
They are not new but some people are still having problems with them. Automatic slack adjusters on air brake equipped vehicles are only automatic if they are working properly. The only way to find out if they are working properly is to include them in a good daily pre-trip inspection. And, besides, it is the law; it is the driver’s responsibility to ensure that the brakes are in adjustment even if it is not the driver’s responsibility to adjust the brakes manually.
Automatic adjusters are very easy to adjust. There is no need for any tools. Simply make a full brake application of 90-100psi and hold that brake application for 2 – 3 seconds so that the air pressure in the brake chamber has a chance to build up to that of the application. Pumping the brakes several times and not holding a full application may not achieve the same result as the air pressure will not have a chance to get to the required 90-100psi in the brake chamber which will cause the adjusting mechanism to work.
The more often full hard brake applications are made the better chance that the brakes will be in adjustment. If the auto slacks don’t appear to be adjusting, then it is time to take the truck to the mechanic who should be trained how to recognize the problem. Manually adjusting automatic slack adjusters just covers up another problem.
When approaching a curve or an intersection where you intend to turn, slow down before you start to turn the steering wheel. When the steering wheels are turned on a slippery road surface they slide sideways. When the steering wheels slide, there is less traction on the road surface and the steering wheels can lock up at lower speeds during a brake application. To direct the vehicle in the intended direction and not end up in a slide off the road, release the brake application. Releasing the brake application before steering allows a better chance to maintain traction. This practice can be used on dry roads as well as slippery roads. Slow down before you turn.