Why Does the Engine Make Abnormal Noises When Braking?
3 Answers
Here are 3 reasons for abnormal noises when braking in a car: 1. Sand in the brake discs. Generally, newly purchased cars do not make abnormal noises when braking. If your car hasn't been driven many kilometers and the brakes are already making noises, it's likely due to particles like sand or iron powder getting into the brakes, causing a sharp sound when braking. 2. Overly hard brake pads. Some newly purchased cars make noises when braking, especially when braking lightly, usually because the brake pad material is too hard. The noise disappears when braking hard. In such cases, we can usually ignore it and let it wear in over time. 3. Severely worn brake pads, requiring repair at a 4S shop.
I've seen too many cases of abnormal engine noise when braking, which can stem from several components. The most common issue lies in the vacuum booster system, as the brake booster pump relies on engine vacuum pressure to function. If the vacuum hose deteriorates and leaks or the booster pump's seals fail, a hissing air leakage sound may occur when braking. Another often-overlooked culprit is the AC compressor – when you brake, the sudden drop in engine RPM causes load variations on the compressor, triggering humming or squeaking noises, especially noticeable with AC on during summer. The belt drive system might also contribute: loose alternator/power steering pump belts or damaged tensioner pulley bearings can produce creaking sounds due to vibration during braking. In some older models, worn engine mount bushings allow slight engine movement during hard braking, resulting in metallic clunking against the frame. These scenarios all pose safety risks. For inspection, start with vacuum hoses and belts, then seek professional diagnosis if needed to prevent roadside breakdowns compromising safety.
My own car developed this issue last year - a gurgling sound from the engine bay when braking after cold starts. After extensive diagnosis, the mechanic found it was a vacuum leak in the intake manifold. Since the brake booster connects here to draw vacuum, any air leakage causes abnormal noises like a broken bellows. Another commonly misunderstood culprit is the AC system: when the compressor clutch doesn't engage tightly at low speeds, braking-induced RPM fluctuations can cause clunking sounds. Belt squealing is also quite common, especially during rainy seasons when moisture makes belts more prone to slipping. These noises become increasingly annoying if left unaddressed - replacing the belt made my car much quieter. It's best to pay attention to these abnormal sounds during daily driving rather than waiting for a roadside breakdown. During routine maintenance, have technicians thoroughly inspect these vulnerable areas - safety always comes first.
