They’re called automatic slack adjusters for a reason, and the manufacturers that make them want to keep it that way.
Commercial Vehicle Safety Alliance (CVSA)'s annual Brake Safety Week is set for Aug. 22-28, placing additional emphasis on one of the leading causes of out of service violations and added pressure on fleets and technicians to get it right. Yet despite years of warnings, automatic slack adjusters (ASA) continue to be manually adjusted by technicians who may not know any better or who may be eager to get a truck out of the shop and back out on the road.
“If a fleet is manually adjusting a slack adjuster regularly it can harm the longevity of the unit,” said Chris Christiansen, warranty/technical services coordinator, Accuride Corporation.
“If a fleet is manually adjusting a slack adjuster regularly it can harm the longevity of the unit.” Chris Christiansen, warranty/technical services coordinator, Accuride Corporation
“The reasons behind adjusting an ASA outside of a brake reline should be investigated such as alignments, bushing wear, wheel conditions, etc.,” Christiansen said.
Throughout the week-long Brake Safety Week campaign, inspectors will conduct North American Standard Inspections of commercial motor vehicles, focusing on the vehicle’s brake systems and components. In addition, inspectors will compile data on brake hoses/tubing – the focus area for this year's blitz.
“Brake hoses and tubing are critically important to the performance of the entire braking system, so it’s important that these components be in good shape and free of kinks,” said Brian Screeton, Bendix supervisor – technical service training. “Visual inspections should also include regular checks of tubing and hose condition, positioning, and connections, both during pre-trip walkarounds and in the shop. Additionally, we recommend that before drivers get on the road, they routinely perform 90- to 100-psi brake applications – with the wheels chocked and the parking brakes released – listening for leaks that might be attributed to hoses and/or tubing.”
During last year’s Brake Safety Week, 12% of the 43,565 commercial motor vehicles inspected were placed out of service for brake-related violations. With out-of-service brake violations continuing to top the annual CVSA International Roadcheck, manually adjusting an automatic slack adjuster can not only lead to more brake problems down the road, it can also lead to accidents.
Following their mandated use on tractor-trailers in 1994 and trailers in 1995, the NTSB issued a scathing report in early 2006 condemning the practice of regularly adjusting ASAs. NTSB ruled an ASA adjustment had led to a runaway truck accident in Pennsylvania in 2003 that claimed the life of the driver and an 11-year-old child riding in a car that the dump truck had struck during its descent on a steep downgrade.
That report, in part, reads: “The drivers and mechanics who manually adjusted the automatic slack adjusters on the trucks involved in the Glen Rock and El Cerrito accidents did not look for underlying problems with the adjusters or related foundation brake components; consequently, they misdiagnosed the brake problems, probably because they were not properly educated on the function and care of automatic slack adjusters and how they relate to foundation brake systems.”
The NTSB went on to write that “warnings in existing materials available to owners, drivers, mechanics and inspectors of air-braked vehicles equipped with automatic slack adjusters have not been successful in communicating the inherent dangers of manually adjusting automatic slack adjusters to correct out-of-adjustment brakes.”
That ruling eventually led to a mandate.
“NTSB sent a directive to the manufacturers of automatic slack adjusters regarding ASA re-adjustment in August 2007,” said Jason Kraus, senior manager of braking components, Meritor.
According to Kraus, that directive requested a change to service literature on the topic of ASA adjustment.
“ASAs should not be manually adjusted to correct excess brake stroke, as doing so is a dangerous practice when a brake is only out of adjustment or over stroke limitations. Excess stroke is an indication of component malfunction that manual adjustment cannot fix." Jason Kraus, senior manager of braking components, Meritor
“ASAs should not be manually adjusted to correct excess brake stroke, as doing so is a dangerous practice when a brake is only out of adjustment or over stroke limitations,” he said. “Excess stroke is an indication of component malfunction that manual adjustment cannot fix. Manual adjustment or de-adjustment shortens ASA life, except Meritor Stroke Sensing ASA due to its unique pull pawl design. A manual adjustment gives drivers false sense that everything is working correctly.”
Keith McComsey, Bendix Spicer Foundation brake director of marketing and customer solutions, said the name speaks for itself.
“Automatic slack adjusters are just that … they should act automatically,” McComsey said. “If a technician feels the need to adjust an automatic slack adjuster, it is because there is some other issue within the drum brake system that should be investigated.
“Automatic slack adjusters should not be manually adjusted in an effort to correct excessive pushrod stroke,” he adds, “because this condition indicates that a problem exists with the automatic adjuster, with the installation of the adjuster, or with related foundation brake components, which manual adjustment will not fix.”
There may be times, however, when manual adjustment is required — like during ASA installation and when brake repairs and overhauls, such as relines, are performed.
“Haldex does not recommend or approve manual adjusting of the automatic brake adjuster except for emergency purposes when the wheel-end brakes cannot be released by air pressure, and when routine brake/wheel-end maintenance is performed like a brake reline,” said Randy Petresh, vice-president of technical services, Haldex Brake Products. “In addition, manual adjustment will mislead diagnosis of wheel-end brake issues during troubleshooting investigations.”
When manual adjustments are necessary, “never use an air impact wrench to adjust an automatic slack adjuster as this can damage the internal mechanism/adjuster,” McComsey said. “Use of wrenches and sockets or ratchets is recommended.”
Lubrication and greasing
Lubrication is a key maintenance component, and McComsey noted there are two reasons to grease a slack adjustor.
“First, it protects the adjuster’s internal gear sets, clutches, and other components from premature wear," he said. "Second, the action of forcing new lubricant into the ASA purges the old grease, along with any contaminants or water that have found their way in. Both support vehicle safety by maintaining the correct brake stroke and providing optimal stopping performance.”
Cleaning the purge slot on the boot, and adding grease until the old grease is fully purged and you see new grease exiting the purge hole, McComsey said "is a requirement," but referred to “manufacturer’s recommendations for lubrication of the adjuster, noting the suggested mileage, frequency and lubricant grade.”
A grade 2 lubricant endorsed by the National Lubricating Grease Institute is recommended for preventive maintenance inspections on Bendix ASAs approximately every three months or 30,000 miles.
Tom Gauerke, national fleet account manager for Chevron Lubricants, noted that it's important to use a non-Moly grease on slack adjustors as the Moly can cause stickiness within the moving parts and the brakes to malfunction.
Techs should be careful not to over-grease, which Patrick Kealy, ZF North America OEM trailer business leader, CVCS division, warns can compromise seals and allow contaminants to enter ASAs and increase wear.
“Any time you’ve got a vehicle in the shop, it’s also worth greasing the S-cam brake tubes and automatic slack adjusters," said Mark Holley, Bendix director of marketing and customer solutions – Wheel-End. "This quick process helps prevent rust and corrosion, and helps keep the slack functioning properly."
Keeping brakes in check
During CVSA's three-day International Roadcheck inspection blitz earlier this year, 26.5% of all vehicle out of service orders were the result of brake system violations. Brake adjustment (12.4%), was No. 4.
“The most common failure of an automatic slack adjuster is when a mechanic or a driver continues to adjust them,” said Kealy, ZF. “They are automatic and therefore typically only need to be adjusted when they are installed for the first time or every time a brake job is performed.”
However, ASAs may be targeted for OOS violations when other brake hardware is actually at fault.
“ASAs often get blamed during CVSA inspections for OOS conditions, but many times the other foundation components are worn down causing overstroke conditions." Jon Erickson, ASA product engineer, Gunite
“ASAs often get blamed during CVSA inspections for OOS conditions, but many times the other foundation components are worn down causing overstroke conditions,” said Jon Erickson, ASA product engineer, Gunite. “Changing the ASA in this instance may allow the system to reset enough to be compliant. Replacing an ASA due to an OOS may get your vehicle back on the road but the other foundation components should be studied at the earliest possible convenience to verify the braking system is in acceptable condition.”
ASAs have been in the market long before they were first mandated in 1994. For instance, Haldex rolled out its first U.S. version in 1980.
“The basic design has been very stable ever since that time except for continuous improvement initiated minor changes in material and processing like seal improvement,” Petresh said. “The only significant change occurred about 10 years ago with the design, development and production of a new model, the self-setting automatic brake adjuster.”
Like many other components that hit the market, ASAs were designed to improve safety and lower maintenance requirements for fleets.
“A truck owner had to make daily inspections or adjustments to the brakes before the automatic slack adjuster was implemented on trucks,” said Eric Iott, product specialist, Meritor. “The inspection expense was large and the potential for error in the adjustment was much greater with manual adjustment slacks.”
Regular maintenance and accurate trouble-shooting remains key to a long, safe service-life devoid of OOS infractions.
Troubleshooting ASAs starts with a stroke test per “the CVSA to verify your brakes are out of adjustment,” Kealy said. “After confirming other components in the foundation brake are working correctly (such as brake shoes, drums, S-Cam, S-Cam bushing, etc.), look at the ASA.
“Back off the brakes to check operation of the ASA,” he adds. “Place a wrench on the adjustment screw and apply the service brakes. You should see the wrench rotate in a clockwise motion which indicates the ASA is taking up the clearance between the drum and shoe. Greasing the S-Cam spline and clevis pin should also be included as part of this maintenance and will help with ASA removal the next time.”
And technicians should always follow manufacturer service requirements and instructions. If the ASA is diagnosed as faulty, replace it with a new one.
“It is not recommended to ‘fix’ an automatic slack adjuster,” McComsey said. “If it is not adjusting properly, or has other damage to it, it should be replaced.”