News

Slack adjusters

May 1, 2001

With the development of automatic slack adjusters (ASAs) has come the misconception that if you install an ASA on your brake system, the stroke will be accurate from then on. But things are never quite that simple. Units can break or can be improperly installed, for example. (See In-box story, p. 16, on recent NTSB slack adjuster recommendations.) Manufacturers are unified in their advice that automatic

Marilyn Wilson

With the development of automatic slack adjusters (ASAs) has come the misconception that if you install an ASA on your brake system, the stroke will be accurate from then on. But things are never quite that simple. Units can break or can be improperly installed, for example. (See In-box story, p. 16, on recent NTSB slack adjuster recommendations.)

Manufacturers are unified in their advice that automatic slack adjusters should be checked on a regular basis, perhaps even as part of a driver's pre-trip inspection. As Dana points out, the term automatic does not give you license to “install and forget.”

To make this procedure easier, Bendix recently introduced the SureStroke Indicator, a “visual indicator of brake-stroke travel that allows the operator to quickly determine if air brakes are adjusted correctly.” By helping to identify problems such as worn, seized or incorrectly installed slack adjusters, the indicator can also help determine whether the ASA is at fault when the stroke isn't right, or whether the brake system itself is to blame.

Bendix also offers a valve (BVA-85) that aids in checking the stroke on slack adjusters. Operated from the dash, it will hold 85 psi in the brake chamber so the driver can walk around the vehicle to check the stroke.

When it comes to adjusting ASA, most manufacturers agree that at minimum this should be done at installation and when brakes are replaced. Some also suggest adjusting ASAs at regular intervals, although overdoing this could lead to premature wear.

In terms of maintenance, keeping ASAs properly lubed is of primary importance. Bendix, which makes the ASA-5 SureStroke, recommends greasing at installation and at every PM or 25,000 miles.

Crewson Brunner recently made Cam-Guard — which prevents the ASA from seizing to the S-cam — a standard feature on its full line of ASAs. The spline is designed with a groove in the center that enables grease to flow to the S-cam when the ASA is lubed. The company first introduced this feature as Auto Grease, but changed the name to minimize the possibility that users will think no greasing at all is required. In fact, Crewson Brunner recommends greasing ASAs at regular intervals.

Dana Spicer, which sells ASAs made by Haldex, offers units with different lubrication requirements: A no-lube version for Spicer No-Lube LMS brakes, with no lube maintenance required during the warranty period (3 yr./350,000 mi.); an ASA for low-lube LMS brakes, with lube intervals of 250,000 mi.; and a more traditional ASA that requires annual lubrication.

Other maintenance recommendations include measuring the stroke to ensure that ASAs are functioning properly. According to Crewson Brunner, this is one of the best ways to check the slack adjuster. Air pressure and torque should also be verified.

ArvinMeritor offers ASAs for all steer, drive and trailer axle brakes, including Q-Plus LX500 Extended Lube for tractor and trailer products. For linehaul applications, the LX500 ASA/brake combination is lubrication-free for 3 yr./500,000 mi.; and for other applications, 1 yr./unlimited miles. But these no- or low-maintenance ASAs are exceptions to the rule when it comes to slack adjusters. Meritor recommends greasing standard ASAs periodically even if they come pre-assembled to the brake.

Last year Haldex introduced a self-setting automatic brake adjuster, the SABA. Designed with a control arm that can be placed in any position, this unit is said to eliminate installation errors. Haldex brake adjusters use a control arm actuation system that allows moving parts to remain sealed behind an O-ring, eliminating linkage pins that can wear prematurely and reducing maintenance requirements. A built-in installation indicator ensures proper installation without the use of templates.

Earlier this year, Gunite introduced an automatic slack adjuster designed specifically for the newest welded clevis, long-stroke brake chamber applications. The Gunite 2000, which provides a perfect fit for these models, requires no external brackets or mounting hardware, reducing installation time and labor, according to the company. Gunite ASAs also feature self-lubricating worm wheels.