The importance of choosing the right replacement friction

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."

That same report bluntly states that the FMVSS 121 testing of small lining samples "is not considered accurate in determining performance on a full size brake," making it abundantly clear that this particular procedure is no longer a reliable barometer of how a brake should perform in today's RSD environment.

The 96' Difference

Using sophisticated vehicle performance testing systems, Bendix compared the 60 mph stopping distance of an RSD-compliant vehicle with OEM high-performance brakes and linings against both pre-RSD original equipment and off-the-shelf aftermarket linings. Despite passing the FMVSS 121 dyno test, neither the pre-RSD OEM friction nor the aftermarket replacement friction met the new 250' RSD requirement.

In fact, when equipped with a popular "20K" (20,000-lb rated) aftermarket friction, the vehicle's stopping distance increased from 215' using the high-performance OEM friction to 311', a stunning 45 percent decrease in performance. That 96' difference in stopping distance, the approximate length of five passenger cars, is a stark illustration of the roadway safety at stake.

It's also worth noting that at 215', the stopping distance for the OEM high-performance friction is 35' below the RSD requirement, demonstrating its ability to far exceed RSD standards.

Because there is no practical "on-the-road regulatory test" of brakes in action, however, drivers of vehicles using aftermarket replacement friction won't know whether their new linings have compromised their stopping power until a real-world situation is at hand. An emergency stop is no time to find out.

The safety concerns associated with substandard aftermarket replacement friction are real.

When the time comes to replace brake linings, fleet owners and operators are best served by relining with high-performance OEM friction. By doing so, they can ensure RSD-level braking performance and enhance highway safety.