The Mystery of Brakes Out of Adjustment

With automatic slack adjusters required by regulation on trucks and tractors since 1994 and trailers since 1995, why do we still have brake adjustment violations? "Defective Brakes" was the number one violation in the 2024 CVSA International Roadcheck.

One reason is that automatic slack adjusters are mechanical devices that, if not properly maintained, can malfunction and contribute to brakes being out of adjustment. Slack adjusters on all commercial vehicles should be inspected and greased every 90 days.

Another reason is the technical function of automatic slack adjusters. Professional drivers maintain a space cushion between themselves and the vehicles in front of them. When applying the brakes, they typically use 15% to 25% air application. Only in defensive situations will a driver apply the brakes with greater than 60% air application. These braking incidents are referred to as “Panic Stops” or “Rapid Deceleration Occurrences.” Analysis shows that most professional drivers require fewer than six such brake applications per 1,000 miles driven.

Most of our Navistar trucks are equipped with “Stroke-Sensitive” automatic adjusters. This type of slack adjuster adjusts the brakes on the return stroke, but only when the brake application exceeds 60%. The better the driver, the less opportunity there is for automatic brake adjustment.

To ensure that brakes remain properly adjusted, we recommend the following:

1. Pre-Trip Inspection: While the unit is parked, complete 10 full brake applications. A slack adjuster will adjust approximately ½ inch with every 10 full brake applications. Including this procedure as part of your pre-trip inspection ensures that your brakes

   

   remain in adjustment. In the event of a roadside inspection, repeat this process beforehand to ensure compliance.

2. Low Air Pressure Warning Device Check: During the pre-trip inspection, drivers are required by the Federal Motor Carrier Safety Administration to check the low air pressure warning device. This should be audible at 60 psi. To check this, the air pressure must be lowered to 60 psi. While performing this check, if a driver fully applies and releases the brakes, the air pressure should drop approximately 4 psi with each application.

Squeaking Brakes

Another condition caused by "feathering" or low-psi brake applications is noisy brakes when stopping. Many times, this results from crystallized brake linings, which occur when brakes are repeatedly applied with low psi. This can be minimized with four or five firm brake applications or rapid deceleration stops. If your brakes are noisy, try bringing the vehicle to a stop using four or five firm brake applications each week. Always ensure no vehicles are following closely when performing this procedure.

Finally, if a driver feels their brakes are not operating normally, they should communicate this to their service provider on their daily vehicle inspection report. Drivers should NOT manually adjust automatic slack adjusters—this should only be performed by a trained technician.

Use the Following Links to Access Idealease Pre and Post trip training videos:

English: 

Tractor Trailer- https://youtu.be/9TL62H5yUQA

Straight Truck- https://youtu.be/rsUTQrN-514

Spanish: 

Tractor Trailer- https://www.youtube.com/embed/529XGiJxTfU

Straight Truck- https://www.youtube.com/embed/SDvbuAuKQLM

International Roadcheck is an annual three-day event during which CVSA-certified inspectors conduct compliance, enforcement, and educational initiatives focused on various aspects of motor carrier, vehicle, and driver safety.

International Roadcheck is the largest targeted enforcement program for commercial motor vehicles in the world, with nearly 15 trucks and motorcoaches inspected, on average, every minute across North America during the 72-hour period.

Since its inception in 1988, more than 1.8 million roadside inspections have been conducted during International Roadcheck. The event also serves as an opportunity to educate both the industry and the general public on the importance of safe commercial motor vehicle operations and the roadside inspection program.

CVSA sponsors International Roadcheck with participation from the Federal Motor Carrier Safety Administration, the Pipeline and Hazardous Materials Safety Administration, the Canadian Council of Motor Transport Administrators, Transport Canada, and Mexico’s Ministry of Infrastructure, Communications, and Transportation.

The next International Roadcheck is scheduled for May 13-15, 2025.

Safely getting in or out of a Commercial Motor Vehicle

Now is a good time to remind drivers to follow the three-point rule when getting in and out of their trucks. During the winter months, footing conditions can be compromised, increasing the risk of slipping or falling.

The three-point rule simply means keeping three out of four contact points (hands and feet) secured at all times to prevent slips and falls. For example, when exiting a truck, a driver should have one hand on the cab handle, one hand gripping the interior door handle, and one foot on a step while the other foot is in transition. This ensures continuous three-point contact for maximum stability and safety.

FMCSA regulations prohibit a driver from beginning or continuing to drive if their ability or alertness is impaired by fatigue, illness, or any other condition that makes it unsafe to operate a commercial vehicle.

Even if a driver holds a valid medical certificate, they are still prohibited from driving a commercial motor vehicle (CMV) if they have a medical condition that is disqualifying or could interfere with the safe operation of the vehicle. Once a disqualifying medical condition is resolved, the driver must obtain re-certification from a Medical Examiner before resuming CMV operation.

Reference: FMCSA CFR 391.45