Conversion to air disc brakes (ADBs) is increasing because they provide some advantages over drum brakes, including shorter stopping distances. Plus, there is virtually no brake fade with ADBs, so torque stays more consistent through the entire stop, says John Thompson, OE sales manager, TMD Friction (www.tmdfriction.com), one of the world´s largest manufacturers of brake friction materials.
Another advantage, he adds, is that “because the braking force of an ADB is simpler than a drum brake – squeezing a flat rotor, compared to the complexity of brake shoes against a drum, the possibility of brake pull on the steer axle is greatly reduced for better straight line stability. Other factors contribute to side-to-side brake pull, but brake geometry is no longer part of it.”
Moreover, ABDs can help shorten vehicle downtime because they are easier to maintain. Depending on such things as the friction level of the material, the truck’s vocation, driver habits, etc., Thompson notes disc pads can last twice as long as drum brakes.
Preventative Maintenance
Disc brakes, as with drum brakes, require proper preventive maintenance (PM) to get the most life and reliability.
“A good PM schedule and inspection procedure are critical to optimizing safety, brake life and cost,” Thompson of TMD Friction says.
He offers this guidance:
- Calipers have wear indicators to give an idea of remaining pad life. The caliper moves to compensate for pad wear. Alignment marks, or a wear indicator pin, will give the approximate pad wear and remaining life. The maintenance manual for the caliper will describe the method used for indicating pad wear and how to read it.
- Caliper assemblies are non-serviceable and should be changed as a unit.
- Technicians need to be well trained when working on brakes.
Check the rotor for scoring, cracking or abnormal wear. Light heat checking, similar to drum brakes, is considered normal. Cracks are not. Refer to the maintenance manual for determining normal and abnormal.
A pad change only requires about 25 percent of the time required for a shoe change, he says, which saves time and money. Once the wheel is removed, new pads can be installed quickly.
Pads
Thompson of TMD Friction says the pad brand purchased and installed is important, and advises purchasing the same lining material the OEM installed on the vehicle when it was new; replace like for like. The reason being: OE brake manufacturers produce the appropriate brake linings for specific vehicle applications to get the best stopping power and wear. Improper replacement friction could compromise performance and safety.
