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Truck Safety Expert:
What Happens When Brakes Are Out of Adjustment?
By Jim Acock
Brake Fade comes from drums heating (expanding) to such a degree that the shoes can’t do an effective job of creating enough pressure / friction to slow that wheel. The thinner the drum is, the quicker it heats and expands.
One should keep in mind that on an 18-wheeler there are 10 separate mechanical systems; one on each end of every axle. This is where the adjustments take place. To have one brake out of adjustment means an unbalanced system and the loss of 10% of the braking or stopping ability of the entire rig. Two out of adjustment means 20% loss, and at this point the DOT Regulations put the rig out-of-service.
You can also find trucks that have an adjustment on one end of an axle, such as 21/8 inches on a C-30 chamber (theoretically in adjustment) but in the use of that brake, the heat developed can quickly put it out of adjustment –especially if the drum is worn down to its limit. One quick stop can put a drum temperature up to 600°. If the adjustment is different on the opposite wheel, then the truck would be operating an unbalanced system. Just stopping at stop lights at proper speeds, there would be very little effect, but a panic stop would indeed affect the system. If there is an accident with a truck involving stopping (brakes), a very intense inspection of the tractor-trailer braking system should take place.
Drivers often take the position that brake inspections are not critical because of the use of the automatic slack adjusters. This assumption is erroneous as the automatic slack adjuster does get out of adjustment, and it is the driver’s job to know the condition of his equipment. Each wheel needs to be checked every day for viability of components (linings, etc.) as well as leaks and adjustments.
Commercial drivers are required by the Federal Regulations to have knowledge of their equipment. For instance, how does the driver know the 10 drums on an 18-wheeler are “sound”? The only way is visually inspect each one and to rap each one of them with a wrench or hammer to make sure they ring like a bell.
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