Reliability, maintenance take center court
Since the government mandated use of automatic slack adjusters on new air-braked vehicles nearly five years ago, the focus has shifted from whether or not to use them in the first place to issues surrounding component life, reliability, and ease of maintenance.
The Bendix SureStroke ASA-5 automatically adjusts the shoe-to-drum clearance every time the brake is applied - without under- or over-adjusting. It's appropriate for on-highway vehicles with AL factors (chamber type times slack adjuster arm length) up to 195.
Adjusting linkage is prelubricated and sealed. And with no brackets or special attachments, no special tools, and an "easy on" yoke, installation and removal are relatively simple. Bendix also offers a reman ASA-5.
Crewson Brunner ASAs are available with the company's Auto-Check brake stroke indicator permanently mounted on the unit. Installed on the side facing the center of the vehicle, Auto-Check enables users to check setup and air chamber stroke without crawling under the truck. To facilitate proper installation, Crewson Brunner supplies a guide that locates the clevis yoke on the chamber pushrod, eliminating trial-and-error when the ASA is placed on the S-cam.
Dana Spicer offers prelubed and traditional automatic slack adjusters, both manufactured by Haldex. Designed for Dana's LMS brake assemblies, the prelubed ASAs were developed for fleets where minimal maintenance during the first 350,000 mi. is a top priority.
The prelubed LMS slack adjusters are available in low-lube and no-lube models. The low-lube version requires some lubrication during the 3-yr./350,000-mi. warranty period, but not nearly as much as traditional slack adjusters. A special flat-head grease fitting accepts synthetic grease. Dana Spicer offers a 6-yr./1-million-mi. warranty on its traditional ASAs, provided proper lube-maintenance schedules have been maintained.
According to Dana, fleets should pay close attention to slack adjuster maintenance, as well as understand how the component's reliability affects lining wear and compliance with FMVSS 121.
Gunite has responded to fleet demands for lower maintenance costs by introducing an ASA with prelubrication between the S-cam spline and slack adjuster to help prevent the S-cam from becoming "frozen" to the slack. In addition, wear points have been reduced to alleviate bushing replacement.
Next January, Gunite will introduce an ASA with a pre-mounted collar-lock clevis, meaning reduced maintenance time. This design allows a technician to dis-assemble the slack adjuster from the brake without having to take pins out.
The importance of checking ASAs accurately is also underscored by Gunite. A common problem is that fleets adjust ASAs manually rather than checking the stroke. For one thing, adjusting slack adjusters too frequently can actually shorten their life. And if the problem lies in the foundation brake itself, adjusting the slack adjuster won't solve the problem.
Haldex Brake Systems offers the AA1 line of automatic brake adjusters (ABAs), preferring this nomenclature to the more traditional "slack adjuster" terminology. A built-in indicator makes initial installation and maintenance easier. Because the adjusters are completely sealed, greasing is only necessary once a year.
The company has developed a lining wear sensor that communicates with electronic braking systems (EBS), providing information that can help regulate brake balance and thus create more even wear. The unit, which slides on the camshaft outside of the automatic brake adjuster, is currently available on Mercedes vehicles spec'd with EBS.
For the future, Haldex envisions fleets using the lining wear sensor in conjunction with an electronic monitoring system to provide information about the exact state of the brake lining.
Meritor Automotive redesigned its automatic slack adjuster a little over a year ago. Available as an OEM spec or aftermarket retrofit, the new unit offers improved reliability through a "pressed in" and sealed actuator boot. A metal retaining ring on the boot forms a seal when the boot is pressed into the slack body, thus protecting the boot from damage.
Designed with a reduced number of moving parts, the Meritor ASA needs no external brackets and has no slip clutches that might wear out. And a pull pawl makes it unnecessary for technicians to remove the pawl when manually adjusting the brake.