Brake Noise Diagnosis on a Customer Vehicle
A 2016 sedan arrives at the workshop with 78,400 km on the odometer. The customer reports a grinding noise from the front when braking and a pedal that feels slightly soft. A junior technician road-tests the car, hears the noise, and immediately proposes replacing all four rotors and pads plus a full brake fluid flush, quoting 4.5 hours labour. You measure the front pads: outer pad on the left has 2 mm remaining, inner pad on the same side has 9 mm. The right front pads are both around 7 mm. Rotor thickness on the left front is 24.8 mm against a minimum of 26.0 mm stamped on the hat. The right front rotor measures 27.1 mm. Brake fluid moisture reads 2.5 percent. The workshop's policy requires a written diagnosis before any parts are ordered.
1. Evaluate the junior technician's proposed repair. What does the evidence support, and what should be done before any parts are ordered?
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The proposal is over-broad and not supported by the measurements. The key evidence is the uneven pad wear on the left front: 2 mm outer versus 9 mm inner on the same caliper. That pattern points to a seized or partially seized caliper slide pin or piston, not general wear across the whole system. Replacing all four corners would hide the fault and the new left pads would wear the same way again.
Before ordering parts, the technician should:
- Strip and inspect the left front caliper: check slide pins for free movement, check the piston for corrosion and retraction, and inspect the caliper bracket.
- Confirm the rotor is genuinely below minimum. At 24.8 mm against a 26.0 mm minimum it is 1.2 mm under, so it must be replaced, not machined.
- Check the right front rotor (27.1 mm) against its own minimum before condemning it.
- Record the moisture reading of 2.5 percent and check it against the manufacturer or workshop specification for a fluid change interval.
Only after that inspection should the repair be quoted. The likely correct scope is a left front caliper overhaul or replacement, left front rotor and pad set, and a fluid change if the moisture exceeds specification. The right side should be assessed on its own measurements, not replaced by default.
2. The customer says a previous shop replaced the front pads only 8,000 km ago. How does that change your reasoning, and how would you explain the situation to the customer?
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It strengthens the case that the fault is mechanical rather than normal wear. Pads with 2 mm remaining after only 8,000 km indicate accelerated wear on one side, which is consistent with a dragging caliper or a binding slide pin holding the pad against the rotor. It also raises a question about whether the previous repair was done correctly, for example whether the slide pins were lubricated and the piston was wound or compressed properly.
The explanation to the customer should be factual and avoid blaming the previous shop without evidence. A workable script: the left front brake is dragging because the caliper is not releasing fully, so the pad on that side has worn from new to 2 mm in 8,000 km while the other side is still at 7 to 9 mm. The left rotor is also below its minimum thickness and must be replaced. The right side does not need replacement based on its measurements. The repair will focus on the left caliper, rotor and pads, plus a fluid check. Document the measurements on the job sheet and get the customer's approval before proceeding, and note that a wheel alignment or suspension check may be worthwhile if uneven wear appears elsewhere.