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TRACTOR-TRAILER COMPATIBILITY
Page 45
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• Excessive wear in linings or pads is the most obvious manifestation of tractor-trailer compatibility problems. So operators focus on the friction material when in actual fact, says Ferodo, it is usually the set up of the braking system.
Incompatibility can arise from different sizes of drum or disc on tractor and trailer, incorrect set up of brake pressures or mismatching of friction materials between axles.
A rig that is correctly set up when it first goes on the road still needs routine checks to ensure it stays that way, points out Ferodo's Don Coffey, OE accounts manager, friction products, because components such as brake bias valves wear. "This has a direct effect on the level of braking force distributed between tractor and trailer. If the brake bias is set up incorrectly then incompatibility of braking forces will occur."
Coffey says trailer wear problems often occur because of mismatched brake sizes. "Trucks are invariably on 22.5in brakes, so the operator really only has a choice as to whether the trailer is on 19.5in or 22.5in brakes.
The smaller trailer brake will get hotter simply because there is less surface area over which the heat can dissipate and that is assuming the braking effort is spread evenly across all axles." The mismatch, says Coffey, explains why operators on heavy-duty operations such as tipping work have wear problems with disc brakes.
Disc brakes begin to work at a lower threshold pressure than drum brakes so when disc brakes are on the front axle of a vehicle with drum brakes on the back, either EBS or a predominance valve is required to ensure all brakes are worked evenly. If the valve is incorrectly set or fails, then too much work may be transferred to the disc resulting in balance and other, associated, problems. EBS cannot adjust the tractor-trailer settings, but does ensure they operate as they were intended.