The importance of brake hose inspection

Brake component manufacturer Bendix acknowledges that brake hoses are only a tiny component in a hydraulic brake system, but they have one of the biggest tasks to perform.

Even though brake hoses may not have the same importance as other components such as brake pads, disc brake rotors, callipers or even the brake master cylinder, they still require regular inspection.

Nevertheless, the humble brake hose is one of the most regulated components of light and medium trucks. Indeed, this indicates how critically important brake hoses are to the overall performance of a hydraulic braking system.

In a nutshell, brake hoses are responsible for carrying brake fluid from a vehicle’s brake lines, fixed to the truck’s underbody, on the last part of the fluid’s journey to the brake callipers located on the wheels. At the business end, there is wheel movement, suspension movement and steering movement, which means that brake hoses need to be flexible yet strong.

Furthermore, the brake hose needs to be robust because the brake fluid travels through it under high pressure once the brake pedal is applied and the brake master cylinder comes into play.

Brake fluid is non-compressible, so the pressure generated at the pedal is maintained to deliver the necessary braking force to bring a vehicle to a safe standstill. In order to maintain this pressure, the hose must retain its original shape.

Consequently, it’s no surprise that the regulations and testing governing the manufacture of brake hoses are strict, with testing benchmarks that far exceed conditions that would replicate real-world driving conditions.

To meet governing current DOT and SAE J1401 standards, brake hoses must pass the following tests:

• Burst pressures – Must withstand water pressure of 4000 psi for two minutes.
• Whip testing – Must endure being continually bent for 35 hours under pressure.
• Tensile testing – Hose assembly must withstand a pull of 325 pounds (approx. 147kg) without separating from its end fittings in a ‘slow pull’ test and 370 pounds (approx. 168kg) in a ‘fast pull’ test
• Cold resistance – Hose is chilled to -45°C for 70 hours and must not show visible cracks when bent around a cylindrical shape.
• Chemical resistance – Hose is subjected to 120°C for 70 hours while filled with an SAE ‘compatibility fluid’; afterwards, the hose is subjected to a 4000 psi burst test.
• Ozone resistance – Hose assembly is exposed to ozone for 72 hours at 40°C and then inspected for cracks under magnification.
• Fitting corrosion resistance – Hose assembly is exposed to salt spray for 24 hours and must show no base metal corrosion to the end fitting surface.

Surprisingly most OEMs don’t have set schedules for replacing brake hoses.

However, Bendix recommends regular inspection of brake lines during vehicle servicing, both visually and by feeling the hoses with the hands to pick up any potential cracks or deformities that are out of sight.

If any of the following flaws are detected during an inspection, you should replace the brake hoses immediately:
• Cracks – even if very small, there’s a risk they’ll grow, leading to possible bursting.
• Bubbles or other deformities – the hose should not change shape under braking pressure (have someone pump the brake pedal during this test)
• Leaks and stains – a leak or stain is not normal and will allow air and moisture into the braking system – this means reduced braking force and increased corrosion within the system.
• Corrosion – while brake hose fittings are plated to resist corrosion, corrosion will occur faster when this protection wears away, potentially compromising the fitting.

Bendix says it is passionate about achieving a better pedal feel and improving brake performance. Often brake performance and pedal feel deteriorate as brake hoses age.

High-quality braided lines regularly produce less than 1.5 per cent line expansion, whereas some OE rubber lines can expand over 3 per cent. Consequently, this means that when you sometimes have over a metre of extended brake lines in your vehicle, the difference in the expansion ratio can allow up to 10mm of extra pedal travel.

Bendix offers braided brake hose kits for many vehicles, including longer-length Ultimate 4WD Brake Hoses for those vehicles equipped with raised suspensions – all meet the SAE J1401 standards as described earlier as a minimum.

Bendix braided brake hoses are constructed from PTFE (Teflon) tubing to deliver higher braking performance with extended durability. This is why the hoses get covered by woven stainless steel 304 braid and finished with the Bendix blue protective layer that further protects the braid from dirt, dust and grime.

While steel braiding isn’t required under SAE J1401, this added component helps deliver a more consistent and firmer brake pedal feel and prevents over-expansion of the hose under high braking pressures.

Bendix has braking consultants available to discuss high-performance braking solutions for your vehicle.