Automobile & Light Truck Certification Test A5 BrakesHydraulic System Diagnosis and RepairMedium
A technician is installing a new section of steel brake line. After double flaring the end of the line, they attempt to connect it to a caliper. The fitting threads on easily, but when tightened, a small leak persists. The technician confirms the flare nut is the correct size and the line is not cross-threaded. What is the MOST likely cause of the leak?
- AThe brake line is made of an incorrect material (e.g., copper).
- BThe flare nut itself is damaged or worn.
- CThe double flare is cracked or improperly formed.
- DThe caliper's female fitting threads are stripped.
Show answer & explanationAnswer & explanation
Correct answer: C. The double flare is cracked or improperly formed.
Even if the flare nut threads easily, a persistent leak after tightening strongly suggests an issue with the sealing surface. A cracked or improperly formed double flare will not create a proper seal against the caliper's female fitting, leading to a leak.
Why the other options are wrong
- A. While copper lines are improper for brake systems due to softness, an incorrect material itself wouldn't necessarily cause a leak at a properly formed and tightened flare; it's more about safety and longevity.
- B. A damaged or worn flare nut might not tighten properly or could deform the flare, but if it threads easily and gets tight, the problem is more likely the flare's sealing surface itself.
- D. If the caliper's female fitting threads were stripped, the flare nut would likely not thread on easily or would feel loose when tightened, which contradicts the 'threads on easily' part of the description.
Improper Double Flare Leak
A persistent leak at a brake line connection, despite proper tightening and correct thread engagement, often indicates a defect in the double flare itself. This could be a crack, an uneven surface, or an incorrect angle, preventing a complete hydraulic seal against the mating fitting.
- Leak after tightening.
- Threads on easily.
- Flare is the sealing surface.
- Cracked or uneven flare.
- Prevents hydraulic seal.
Memory trick: The flare's the face, if it's not smooth, the fluid finds its escape proof!