Automobile & Light Truck Certification Test A5 BrakesDisc Brake Diagnosis and RepairMedium
A technician is installing new brake pads on a vehicle equipped with a single-piston floating caliper. After installation, the technician notices that the inner brake pad is dragging slightly against the rotor while the outer pad has sufficient clearance. What is the MOST likely cause?
- AThe master cylinder is faulty.
- BThe brake hose is restricted internally.
- CThe caliper guide pins are seized or corroded.
- DThe caliper anchor bolts are over-torqued.
Show answer & explanationAnswer & explanation
Correct answer: C. The caliper guide pins are seized or corroded.
In a floating caliper system, the caliper must slide freely on its guide pins to center itself over the rotor and allow both pads to retract. If the guide pins are seized or corroded, the caliper cannot float, leading to uneven pad retraction and dragging, often on the inner pad.
Why the other options are wrong
- A. A faulty master cylinder could cause a spongy pedal or a brake drag on all wheels, but not typically a specific dragging of only the inner pad on one caliper.
- B. Internal hose restriction would typically cause the caliper to apply pressure and not release, affecting both pads or causing a general drag, not specifically one pad while the other is free.
- D. Over-torqued anchor bolts might make removal difficult but wouldn't directly cause dragging of one pad while the other has clearance.
Floating Caliper Operation
A brake caliper design where one or more pistons push a single pad, and the caliper body slides on guide pins to apply pressure to the opposite pad.
- Relies on guide pins for lateral movement.
- Piston(s) on one side only.
- Equalizes pressure between inner and outer pads.
Memory trick: Smooth slides keep the brakes aligned.