Top Signs Your Air Brakes Need Immediate Repair

The Importance of Air Brakes

Unlike passenger vehicles that rely on hydraulic brakes, heavy-duty trucks utilize compressed air to deliver the stopping power required to manage their size and weight. These systems are designed with redundancy and reliability in mind, but that doesn’t mean they’re immune to failure. Brake issues often start small, but if left unchecked, they can escalate.

Hissing or Air Leaks While Parked

One of the most common signs of a failing air brake system is audible air leaks. If you hear a persistent hissing sound after the truck is shut off or while it's parked, that likely indicates:

• A leaking air line
• A damaged air tank check valve
• A faulty push-to-connect fitting.

Compressed air leaks reduce system pressure and may lead to automatic emergency brake engagement, a hazardous scenario if you’re mid-haul or merging lanes. Check around fittings, tanks, and valves for moisture or wear, and don’t delay in replacing compromised components.

Slack Adjusters Out of Spec

If your slack adjusters are misaligned or have excessive travel, your brake response time is dangerously compromised. Slack adjusters play a dual role—they translate pushrod movement into cam rotation, and they automatically compensate for brake shoe wear. When out of adjustment, stopping distances increase, and in extreme cases, brakes may not engage at all.

DOT (Department of Transportation) mandates that manual slack adjusters be adjusted regularly, while automatic slack adjusters must be replaced if they no longer self-correct. Either way, this isn’t a component to ignore.

Spongy or Inconsistent Pedal Feel

Although your foot isn’t applying direct pressure (as it would in a hydraulic system), pedal feel still matters. If the brake pedal feels "spongy," or if its resistance fluctuates during operation, there may be an issue with air pressure regulation, often stemming from the:

• Air compressor
• Air dryer
• Control valves

An inconsistent pedal can also suggest moisture contamination, particularly if the air dryer isn’t effectively removing condensation. That moisture can freeze in colder temperatures, causing complete system lockup.

Brake Drag or Overheating

After a long descent down Utah’s mountainous terrain, a hot brake system isn’t unusual. But when you notice persistent brake drag, it’s time to investigate. This may indicate:

• A stuck S-cam
• Seized return springs
• A malfunctioning service chamber diaphragm that isn’t retracting properly

Overheated brakes lose friction efficiency, glaze the brake shoes, and increase the likelihood of thermal cracking in the drums. If your wheels are too hot to touch post-haul, you're due for an inspection—immediately.

Vehicle Pulling to One Side During Braking

If your rig pulls to one side when braking, it’s often a symptom of uneven braking force between axles. This could be caused by:

• A blocked airline
• Asymmetric brake shoe wear
• Malfunctioning slack adjusters on one side

Beyond creating unpredictable handling, this also increases tire wear and stress on the driveline and suspension components. This isn’t just annoying—it’s dangerous.

Low Air Pressure Warning Light Stays On

A constant low-pressure warning light or buzzer is one of the clearest signs your air system is not maintaining pressure. Most systems require between 90–120 psi to operate properly. If pressure falls below 60 psi, your spring brakes may activate automatically.

Potential culprits include:

• Failing air compressor
• Leaking air tanks
• Clogged air dryer
• Broken pressure protection valve

This is one of those no-brainer red flags. Don’t ignore it. Investigate before the truck investigates the ditch.

Brake Fade or Weak Braking Power

If your truck is taking longer than usual to stop—even with a full press of the pedal—you may be experiencing brake fade. This often occurs when friction materials overheat or when the air supply can’t maintain pressure during repeated braking.

Weak braking power can also point to:

• Worn out brake shoes
• Cracked or out-of-round brake drums
• Compromised S-cam bushings

Any of these conditions increase stopping distance and reduce your ability to control loads safely, especially when descending grades.

Excessive Moisture in Air Tanks

Air tanks are supposed to hold dry, compressed air, thanks to the air dryer. But if you routinely find moisture during daily tank draining, your air dryer might be compromised. Moisture in the lines can corrode components, clog valves, and in freezing conditions, create ice blockages that disable brakes entirely.

Routine draining is essential—but if the tanks fill back up with water faster than usual, that’s your signal to check the air dryer filter element or heater unit.

Vibrations or Pulsations During Braking

Any kind of vibration, judder, or pulsation during braking typically indicates warped brake drums or unevenly worn brake shoes. In some cases, improperly torqued wheels or misaligned axles can cause this too.

If you’re noticing this while braking from highway speeds, especially under heavy load, the system needs to be inspected immediately to avoid total brake failure.

What to Do if You Suspect a Problem

The air brake system is nothing to play around with. If you observe any of the above signs:

1. Immediately conduct a full brake system inspection.
2. Do not operate the vehicle until the issue is identified and repaired.
3. Check your maintenance logs to ensure you’re adhering to scheduled services.
4. Contact a certified diesel technician in your area for proper diagnostics and repair.

Address Brake Issues Immediately

Hissing air leaks, dragging brakes, poor pedal feel, or even dashboard warnings should never be dismissed. Early detection, paired with regular preventive maintenance, is the only path to keeping your rig safe and compliant.

If you require air brake maintenance near St. George, UT, reach out to our team at Amoretti Diesel Repair today.