Expert Maintenance and Troubleshooting Insights for Technicians, Fleets, and Drivers 

By Bendix Commercial Vehicle Systems LLC 

With the new year now here, it’s a good time to both look back and prepare for the road ahead. This edition of the Bendix Tech Tips Series addresses four of the most common maintenance questions that the Bendix Tech Team addressed in 2024. The Bendix Tech Team is an expert technical support group providing service advice, brake system troubleshooting, and product education. 

What If My Air System Is Slow to Build Pressure? 

“Air systems have gotten more complex and interconnected as they’ve been tasked with delivering clean, dry air to more and more vehicle systems, and this has led to some misconceptions about maintenance and troubleshooting,” said Brian Screeton, Bendix’s manager of sales technical training. “But the basic operation of the compressed air system itself is relatively easy to understand, and with a little patience and due diligence, you can often save yourself some real headaches in the shop.” 

Screeton noted that it’s important to look for smaller problems with simpler fixes before jumping into the process of a major repair: In this particular case, technicians troubleshooting the air buildup need to make sure to check the discharge line between the air compressor and the dryer.  

According to Screeton, “This connection can become restricted by carbon accumulation or develop pin holes that will cause a slow- or no-build situation regardless of the condition of the compressor. Most important, it will only leak when the engine is running, so it is hard to hear and troubleshoot without using soapy water while the engine is running. Unfortunately, it’s often the last thing checked after time and money have already been spent installing a new compressor or dryer.” 

Why Is the Foot Valve Leaking With No Foot on the Pedal? 

“This is another situation where it’s easy to leap to replacement of the foot valve – and we understand, because that seems to make the most sense when air is coming out of that exhaust port when the pedal isn’t being pressed,” Screeton said. “The truth is this issue isn’t typically caused by a bad foot valve at all – it’s usually an air back feed from another valve that is taking the quickest path to exhaust.”  

In this case, the proper move before replacing the foot valve is to remove all its delivery lines and check to see which – if any – has air coming out. Once that’s determined, technicians can follow the line(s) back toward the real problem. 

Why Is the Drive Axle Service Relay Valve/Traction Control Valve Leaking When the Parking Brake Is Released? 

This issue understandably can be confusing – but again, it’s important to thoroughly inspect and troubleshoot before replacing the relay valve. While that’s the one that is audibly leaking, this issue is most often caused by a failed brake chamber center seal, or a leaking double-check valve for anti-compounding.  

Diagnosing the leak begins by removing all delivery lines from the Service Relay or Traction Control valve and checking to see which – if any – is exhausting air. Then, with the vehicle wheels chocked, release the parking brake. If one or more brake chamber is leaking, then one or more of the delivery lines will begin to back feed air out of a disconnected line(s). Trace the line to the source of the back feed. 

Screeton reiterated the importance of understanding this, because the root cause of the leak may potentially be due to a faulty anti-compounding feature in the parking valve – not a failed brake chamber center seal. As a result, conducting the line tracing process can help detect and identify the suspect valve. 

What’s Causing the Calibration Error With My Forward-Facing Camera? 

Technologies like the family of Bendix^® Fusion^™ advanced driver assistance systems typically include forward-facing cameras to collect the information that helps enable collision mitigation, lane departure warnings, and other capabilities. These cameras must be properly positioned and accurately mounted on the inside of a vehicle’s windshield to function properly and comply with regulations addressing in-cab obstructions of a driver’s view. 

“It’s not uncommon for us to get calls about error codes related to the image processor and calibration,” Chad Benesh, supervisor of the Bendix technical support team, said, “and most of the time, it turns out that the mounting bracket that holds the camera is simply not installed properly. 

“This is an easy fix, but it’s got to be done right: You’ll need to refer to the Service Data Sheet and use measurements to make sure that the bracket is in the correct place and held there using only the adhesive that it comes with. Attaching the bracket with tape or a hook-and-loop closure material may not seem like it would make a difference, but it’s often found to be the cause of these error codes.” 

Have your own questions? Contact the Bendix Tech Team at 1-800-AIR-BRAKE (1-800-247-2725), option 2. You can find complete maintenance and troubleshooting information in the library of Service Data Sheets and Technical Bulletins located at B2Bendix.com and bendix.com. More information from the Bendix Tech Tips series is available in the Bendix multimedia center at knowledge-dock.com. The Bendix On-Line Brake School (brake-school.com) and B2Bendix.com offer additional instructional videos and interactive education on wheel-ends, air systems, and electronics. 

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