A technician is inspecting a vehicle with a complaint of delayed brake release on one front wheel. After checking for caliper issues and hose restrictions, they decide to test the flexible brake hose using a pair of vice grips. They clamp the flexible hose leading to the affected caliper and then depress the brake pedal. If the hose is internally collapsed, what would the technician observe when clamping the hose and depressing the pedal?
- AThe fluid would bypass the clamp and still flow freely.
- BThe brake pedal would feel firmer.
- CThe brake pedal feel would remain unchanged.
- DThe brake pedal would feel softer.
Show answer & explanationAnswer & explanation
Correct answer: B. The brake pedal would feel firmer.
If the flexible brake hose is internally collapsed, it acts as a one-way valve, allowing fluid to flow to the caliper but restricting its return. Clamping a good hose would prevent fluid from reaching the caliper, making the pedal feel firmer due to the reduced volume to pressurize. However, if the hose is already collapsed internally, clamping it externally would not significantly change the already firm pedal feel (from the restriction), or it might even make it slightly firmer if there was still some slight return flow, but the key is that it prevents further fluid movement OUT of the master cylinder into that clamped circuit, leading to a firmer pedal. The question is a bit tricky, but the logic is that clamping a good hose makes the pedal firmer because it reduces the volume. An already collapsed hose would already cause a firmer pedal.
Why the other options are wrong
- A. Vice grips are designed to fully clamp a flexible line, preventing fluid flow. If fluid still flowed, the clamp was not effective.
- C. If the pedal feel remained unchanged, it would imply the clamp had no effect, which is unlikely if applied correctly, or that the issue is elsewhere. A collapsed hose, even before clamping, would affect pedal feel by restricting return flow.
- D. A softer pedal would indicate fluid escaping or being bypassed, not a restriction.
Collapsed Flexible Brake Hose Test
To diagnose an internally collapsed flexible brake hose causing delayed brake release, clamp the suspect hose with vice grips (or a specialized brake line clamp). Depress the brake pedal. If the pedal becomes significantly firmer than before, it suggests the hose was the culprit, as the clamp is mimicking its internal restriction and preventing fluid return.
- Causes delayed brake release.
- Acts as a one-way valve.
- Clamping restricts fluid.
- Pedal feels firmer if good.
- If already collapsed, clamping will still make pedal firmer due to reduced volume.
Memory trick: Clamp the hose, feel the squeeze; if the pedal's firm, you're at ease (with your diagnosis).