Automobile & Light Truck Certification Test A5 BrakesHydraulic System Diagnosis and RepairMedium
A technician is diagnosing a spongy brake pedal on a vehicle. After inspecting for external leaks and finding none, they decide to bleed the brakes. During the bleeding process, they notice that the bleeder screw on one caliper is loose and allows air to be drawn IN when the pedal is released. Which of the following is the MOST appropriate action?
- ATighten the bleeder screw and re-bleed that caliper.
- BContinue bleeding, as the air will eventually be pushed out.
- CReplace the bleeder screw and the caliper.
- DApply thread sealant to the bleeder screw and re-bleed.
Show answer & explanationAnswer & explanation
Correct answer: A. Tighten the bleeder screw and re-bleed that caliper.
A loose bleeder screw will allow air to be drawn into the system when the pedal is released, preventing effective bleeding. The most appropriate first step is to simply tighten the screw and re-bleed to ensure a proper seal.
Why the other options are wrong
- B. Continuing to bleed with a loose screw will only draw more air into the system.
- C. Replacing the caliper is excessive if only the bleeder screw is loose. Replacing the screw might be needed if it's damaged, but tightening is the first step.
- D. Thread sealant is generally not recommended for bleeder screws as it can contaminate the brake fluid and interfere with future bleeding.
Bleeder Screw Function
A threaded valve on a brake caliper or wheel cylinder, used to release air and old fluid from the hydraulic system during bleeding.
- Must be sealed to prevent air intrusion.
- Opened to release fluid/air, closed to prevent air entry.
- Improper sealing causes air to be drawn in.
Memory trick: Loose screw, air will accrue, tighten it true.