Automobile & Light Truck Certification Test A5 BrakesHydraulic System Diagnosis and RepairMedium
A technician is inspecting a vehicle for a brake fluid leak. They discover a small leak at the connection point between a steel brake line and a brass fitting. Which of the following is the MOST likely cause of this leak?
- AContaminated brake fluid causing corrosion at the joint.
- BIncorrect thread pitch on the flare nut, leading to cross-threading.
- CUnder-tightened flare nut, allowing fluid to seep past the flare.
- DExcessive tightening of the flare nut, causing a cracked flare.
Show answer & explanationAnswer & explanation
Correct answer: C. Under-tightened flare nut, allowing fluid to seep past the flare.
The most common and straightforward cause of a leak at a flare nut fitting is that it is simply not tightened enough. This allows fluid, under pressure, to seep past the seal created by the flare. While other issues can cause leaks, an under-tightened connection is a frequent culprit.
Why the other options are wrong
- A. While contaminated fluid can cause long-term issues, it's less likely to be the *direct* and immediate cause of a leak at a mechanical fitting joint compared to improper torque.
- B. Incorrect thread pitch would likely prevent the nut from threading on properly at all, or cause immediate severe damage, rather than a 'small leak'.
- D. Excessive tightening can indeed crack a flare, but an under-tightened nut is a more frequent and simpler cause of a leak.
Brake Line Flare Nut Leak Causes
Reasons why a flare nut connection on a brake line might leak, focusing on installation errors.
- Proper torque is crucial for a leak-free seal.
- Under-tightening allows seepage.
- Over-tightening can damage the flare itself.
Memory trick: Flare leaks: too loose to seal, or too tight to hold.