Highway safety and stopping power are always at the forefront of discussions within the commercial vehicle industry. This is even truer this year, as the second, and final, phase of the federal government's Reduced Stopping Distance (RSD) regulations for Class 8 tractors is set to take effect.
To ready the commercial vehicle industry for the RSD Phase One compliance date in August 2011, brake manufacturers pushed foundation drum brake technology forward, developing more advanced systems, including larger brake sizes and improved friction material - to meet the new standards and help enhance highway safety. These new high-performance drum brakes reduced stopping distances, often exceeding the mandate, while performing better and with significantly less fade than previous generations of brakes.
Phase One of the new RSD rules impacted new three-axle tractors with a gross vehicle weight rating (GVWR) up to 59,600 lbs, or roughly 80 percent of new tractors. Phase Two, which begins this August 1, is aimed at bringing the remainder into compliance: two-axle tractors and severe service tractors with a gvwr above 59,600 lbs.
Wrong Relining Decisions
Today's improved drum brakes help fleets and drivers meet the RSD regulations and support the mandate's goals of improving safety, avoiding highway fatalities and reducing the number of rear-end collisions.
Yet, a single routine maintenance decision can all but undo that progress, compromising both safety and performance. That decision, relining these high-performance drum brakes with aftermarket linings not specified by the original equipment manufacturer (OEM), can significantly reduce stopping capability and compromise braking performance.
Many of the brakes developed for RSD compliance in 2011 are coming due for relining, and it's essential to choose the right replacement friction.
Why Advanced OEM Friction Matters
Brake manufacturers aren't the only ones noting the distinction between OEM replacement friction and low-cost, low-quality aftermarket linings. Recommended practices of the Technology and Maintenance Council (TMC) of the American Trucking Associations note, "It is essential that the replacement brake linings function as well as the material originally supplied on the vehicle."
Designing and spec'ing brake systems is a full-time priority for the engineering teams at Bendix, and it presents complex challenges and variables such as axle rating load, wheelbase and tire size. With safety top of mind, these engineers create comprehensive brake systems and specify the most effective friction materials for use in those brakes.
Aftermarket replacement linings, produced without use of the exact specifications required by each OEM-designed system, are not engineered to the same standard.
As a result, OEM replacement linings designed for high-performance, RSD-compliant braking systems perform significantly better than pre-RSD original equipment linings and traditional aftermarket brake linings. They also maintain their performance levels much more effectively when subjected to the temperature increases that occur during brake usage.
FMVSS 121 Causing Confusion
Part of the confusion surrounding friction replacement arises from the test standard known as Federal Motor Vehicle Safety Standard (FMVSS) 121. The confusion lies in the use of dynamometer testing, which has become outdated in the new RSD environment.
Although results of the test are often viewed as an indicator that a brake lining will supply the torque output needed to stop a vehicle within the new standards, this is not necessarily the case. Even though they may be FMVSS dynamometers certified to the old standards, these linings simply cannot meet today's higher Reduced Stopping Distance vehicle performance requirements.
Additionally, FMVSS 121 does not take into account the weight transfer that occurs in a braking vehicle, particularly the addition of weight to the steer axle. The TMC's aftermarket brake lining classification report notes the following shortcoming: "Brakes relined with certain aftermarket materials can have reduced braking output, cause a shift of work to brakes on other axles and reduce the overall stopping capability of the vehicle."
Conclusions drawn from Bendix stopping-distance testing and analysis.