Spongy, Vibrating or Squealing Brakes: What Causes Them

Urgent first: when to stop driving

If the brake pedal goes to the floor, sinks slowly under steady pressure, or the car takes much longer to stop, do not continue driving. A red brake warning light, a strong smell of burning from a wheel, or the car pulling hard to one side when you brake are also reasons to stop somewhere safe and arrange recovery or an inspection.

We would rather you had a brake problem looked at needlessly than ignored. The rest of this article is about causes, but anything on that list is a safety matter first.

Spongy pedal: air and fluid

A soft or spongy pedal that needs pumping or travels further than it used to often means air in the hydraulic system. Air compresses where fluid does not, so some of your pedal effort is wasted squashing bubbles. It can follow earlier brake work that was not bled properly, or arise from a leak letting air in.

Old brake fluid is the other common cause. Fluid absorbs moisture over time, and when the brakes get hot the water can boil, creating vapour that acts like air. A flexible brake hose that is swelling internally, or a failing master cylinder, can feel similar. All of these need a proper inspection.

• Air in the lines after previous work or a leak
• Moisture-laden old fluid that is overdue for replacement
• Swollen or perished flexible hoses
• A master cylinder passing fluid internally
• Fluid leaks at pipes, calipers or wheel cylinders

Vibration and shudder when braking

A pulsing pedal or a steering wheel that shakes under braking is most often disc related. If a disc has uneven thickness or has picked up uneven deposits from the pads, each rotation gives a small pulse. This is typically described as warped discs, though the true cause varies.

Not every vibration comes from the brakes, though. Worn suspension parts, damaged tyres and wheel bearings can all shake the car, and they can feel worse under braking when weight transfers forward. A road test and inspection separate them.

Squealing, scraping and sticking calipers

Squeals can be as harmless as light rust on the discs after the car has stood in damp weather, which clears after a few stops. A persistent squeal can mean worn pads, hardened or glazed pads, or missing anti-rattle hardware. Scraping means the friction material may be gone.

A sticking caliper is a more significant fault. The caliper piston or slider pins seize, so the pad stays pressed lightly against the disc. Signs include a car that pulls to one side, a burning smell, one wheel noticeably hotter than the others, and heavy wear on one pad. Left alone, it overheats the brake and wears the parts out quickly.

Pad glazing and what to do

Pads can glaze if they have been overheated, for example by hard braking on a long descent, or by regularly dragging. The surface goes shiny and hard, braking feels weaker and the pads may squeal. Sometimes they can be rubbed down, but often replacement is the sound answer.

At Banks of the Tyne we deal with brake repairs, from pads and discs through to fluid and caliper problems, and we will explain what we find in plain terms. Cost depends on the fault and the parts required. If you are unsure whether your symptom is urgent, treat it as urgent and ask.

Describe the symptom as precisely as you can when you book in: whether the pedal is soft from the first press or only after repeated braking, whether the vibration appears at motorway speed or low speed, and whether the noise comes at the start of a journey or all the time. Those details narrow the search considerably.

Frequently asked questions