Enhanced Braking

New federal braking regulations for heavy trucks

Solutions available to meet the new requirements include higher performance steer axle drum brakes, which include larger diameter drum brakes, wider brake shoes/linings, air disc brakes or a hybrid combination of disc front and rear drum brake systems.

Manufacturers will offer options, and it will be up to the OEM truck builders to decide, by platform, how they will meet this regulation, says Doug King, marketing manager for Bendix Spicer Foundation Brake. From the work conducted by the industry to date, it is anticipated that there won't be any one solution forced on any fleet.

Bendix Spicer Foundation Brake, a joint venture of Bendix Commercial Vehicle Systems and Dana Commercial Vehicle Products, is a single, complete source for OEM brake system design, manufacturing, hardware and support for all foundation brake components and actuation systems, as well as all-makes coverage of medium and heavy duty aftermarket parts.


The baseline brake today on a three-axle tractor with a gvwr of 59,600 pounds or less is 15-by-4-inch drum brakes on the steer axle and 16.5-by-7-inch drum brakes on the drive axles, says ArvinMeritor's Pennington. Options to meet the braking requirements include:

• 15-by-5-inch or 15-by-6-inch drum brakes on the steer axle and 16.5-by-7-inch drum brakes on the drive axles.
• 16.5-by-5-inch or 16.5-by-6-inch drum brakes on the steer axle and 16.5-by-7-inch or 16.5-by-8.63-inch drum brakes on the drive axles.
• Air disc brakes on the steer axle and 16.5-by-7-inch or 16.5-by-8.63-inch drum brakes on the drive axles.
• Air disc brakes on the steer and drive axles.

Each progressive option provides more and more performance, he says.

There is already a trend to a wider drive axle drum brake for more consistent braking torque (less in-stop fade) and longer life when it is combined with the 16.5-by-5 inch steer axle drum brake, notes Pennington.

Test data supports that the optimum solution for best stopping performance is air disc brakes all around. All major tractor OEMs currently have air disc brakes as an option on many of their vehicles.

From a service standpoint, the new brake systems will not necessarily have components that may be interchangeable with the brakes on vehicles today, he says. The new brake assemblies will be specifically designed solutions from each brake suppliers.

Truck OEMs are in the process of deciding which brakes will be standard and which will be optional to give the required stopping distance, says Chuck Eberling, principal engineer, modules and systems integration, Bendix Commercial Vehicle Systems.

"These decisions are being made by weighing the impact of those choices on their whole operation, including their production line, vehicle weight, vehicle complexity and part numbers in their system," he says. "The OEMs are asking questions like: 'Am I going to change the foundation brake more, or am I going to change the system more?,' and 'How am I going to do this - by slightly touching each system or by performing major modifications to one system?'"

But in general, no major changes are anticipated.

It should be noted that truck OEMs have been using larger drum brakes and air disc brakes over the past five years or so and have had good, positive experiences with their products, says Pennington. They have already made some adjustments to axles and suspensions and their bracketry because of brake packaging requirements, but there is still some more work to be done.

For example, some traditional steer axle knuckles are not particularly air disc brake friendly. Many recently engineered knuckles offer both air disc brake compatibility as well as ease of service and overall weight savings. This allows room for the caliper to slide to compensate for the pad and rotor wear.


It is anticipated that the new braking regulation is not going to significantly impact the amount of drum brake maintenance that is needed, says Bendix Spicer Foundation Brake's King. Better torque balance between the steer and drive axle may better balance the maintenance schedules of all axles. In fact, air disc brake solutions actually reduce maintenance time while extending service intervals.

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