Trucks are an essential industry in Australia. They travel millions of kilometres in some of the world’s harshest conditions, and that means air leaks can quickly become a serious problem.
Air leaks reduce braking performance and fuel efficiency, and create a major safety hazard on the road. If you want to avoid being stranded by leaky air brakes, it’s important to invest in regular brake maintenance.
In this article, we learn how to identify and fix air leaks in your braking system, and some of the common causes of these leaks.
How Do Air Brakes Work?
Trucks and heavy vehicles use compressed air to transmit braking force.
Air brakes consist of a compressor, air reservoirs, valves and chambers. These systems carry pressurised air that operates actuators. When the brake pedal is depressed, these actuators push the brake shoes against the rotor or drum, causing the truck to come to a stop.
Air brakes offer better performance for heavy vehicles that need significant stopping force. The only challenge is that air brakes are under a constant pressure of between 100-120psi. Maintaining this pressure puts strain on seals and fittings, which can lead to air leaks that reduce braking performance.
Normal operation vs leaking system
Air brakes work by maintaining steady air pressure, usually between 90 and 120 psi. In normal operation, the system holds pressure with minimal loss, giving you consistent, firm braking.
A leaking system, however, struggles to maintain pressure, causing the compressor to run more often and triggering low-air warnings. You may notice slow pressure build-up, weak brake response or hissing sounds around hoses and fittings.
How to Find an Air Leak in Your Brake System
Air leaks in your truck’s braking system can cause a partial or total brake failure. The simplest way to locate an external leak (e.g. from a faulty hose fitting) is to use a diluted mixture of soap and water:
Common Causes of Air Leaks on Trucks
Air brakes need regular maintenance to prevent leaks and ensure the system functions properly. It’s normal for air systems to degrade due to:
Each component of your air system is joined with fittings. These fittings are typically made of copper, brass or nylon. Even when they’re brand new, fittings can cause air leaks due to incorrect installation or manufacturing errors.
How to Find an Air Leak in Your Brake System
Air leaks in your truck’s braking system can cause a partial or total brake failure. The simplest way to locate an external leak (e.g. from a faulty hose fitting) is to use a diluted mixture of soap and water:
- 1Prepare the Solution
Mix 2 tablespoons of liquid dish soap with 500ml of water in a spray bottle
The solution should be soapy enough to create bubbles but fluid enough to spray easily
- 2Prepare the System
Ensure the truck is parked safely with wheels chocked
Build up air pressure to operating level (typically 120-125 psi)
Turn off the engine but keep the system pressurised.
- 3Systematic Application
Begin at the compressor and work methodically through the system
Spray soap solution on these components in sequence:
Compressor output fittings
Dryer connections
Main reservoirs and valves
Supply lines to brake chambers
Relay valves and brake chambers
Gladhand connections
- 4Interpreting Bubbles
Small, slow-forming bubbles: minor leak, monitor but may not require immediate repair
Rapid bubbling: significant leak requiring prompt attention
Foam or large bubbles: critical leak needing immediate repair
No bubbles after 30 seconds: the area is likely leak-free
This is easiest to do when without a load or trailer attached. If you are working in a quiet area, you may be able to hear an air leak, but small leaks will be harder to identify.
But this method is only effective for external air leaks. Air leaks may also occur between faulty valves within the braking system. These issues can be harder to identify, and you’ll need to ask a diesel mechanic to look at the truck.
Get Air Leaks Diagnosed by Kel Stanton’s Mobile Diesel Service
Leaky air brakes can leave you stranded on the side of the road. When you have places to be, Kel Stanton’s Mobile Diesel Service can get you moving again.
Our technicians are experts in air brakes, so we can identify and repair any leaks in the system. Contact us to book an appointment!
How to Fix an Air Leak on a Truck
Leaking air brakes is a roadworthy fail and a serious safety hazard. It’s important to find and fix air leaks as soon as possible.
Unfortunately, it’s not always that easy. There’s no such thing as a perfectly sealed system. It’s normal for very small amounts of air to leak out of fittings during use. The problem occurs when fittings, hoses and seals begin to break down. These issues all create small leaks that are almost impossible to detect without specialist equipment.
In most cases, you will need to take your truck to a qualified mechanic to diagnose and repair an air leak. Your mechanic has access to diagnostic tools such as ultrasonic leak detectors that can identify tiny leaks in minor components.
With these specialist tools, a mechanic can examine each part of your braking system, locate the leak and perform the repairs you need.
Air Brake Maintenance
Proper maintenance is essential for keeping truck air brakes safe, responsive and compliant with heavy-vehicle standards. Air brake systems rely on clean, dry air and tightly sealed lines, so even small issues can quickly escalate into dangerous faults.
Drivers should also monitor warning lights, gauges and any change in brake feel, as early detection prevents costly repairs. Above all, a consistent maintenance routine is the key to reliable air-brake performance.
Preventive Maintenance Schedule
Daily, weekly or fortnightly checks help you spot potential issues before they turn into big problems. Combining these with annual maintenance and major service intervals should ensure your braking system meets regulatory roadworthy standards.
Inspection Checklist
A thorough inspection checklist helps drivers and mechanics catch issues early. Key items include:
- Confirming air pressure builds to full range within normal time.
- Listening for leaks around hoses, couplings and valves.
- Checking brake linings and drums for wear or contamination.
- Inspecting air tanks for moisture and draining regularly.
- Testing the parking brake and emergency brake functions.
- Ensuring slack adjusters maintain correct pushrod travel.
- Verifying that warning lights, buzzers and gauges operate correctly.
Regular use of this checklist supports safe braking performance and reduces the risk of roadside failures.
Keep Your Trucks and Machinery in Perfect Condition with KS Mobile Diesel!
Your brakes work hard every day. They need to stop tonnes of steel while withstanding dirt, grime, chemicals and thousands of kilometres on the road.
When you have places to be, the diesel repair service team at Kel Stanton’s Mobile Diesel can ensure you’ll never be stranded by air leaks!
Kel Stanton’s Mobile Diesel Service is an experienced mobile diesel mechanic that works all over Brisbane and South East Queensland. We specialise in providing maintenance and repairs for all types of vehicles, trucks, machinery and diesel equipment.
If you need a mobile truck mechanic, contact us and make a booking today!
Frequently Asked Questions
Signs include a hissing noise near hoses or fittings, slow air pressure build-up on startup, frequent low-air warnings, and longer than normal stopping distances.
Yes. Try idling the engine, shutting it off, then spraying a soapy water solution over air lines, fittings and tanks. Bubbles will form where air is escaping.
Visual and pressure checks should be done daily or before each trip. More thorough inspections (hoses, fittings, tanks) can be scheduled monthly or at regular maintenance intervals.