A high-pitched squeal usually means the pads are close to worn out, a grinding noise means they already are, and brake fluid needs changing on a time schedule, typically every two to three years, no matter how little you drive.
How pads wear: every stop scrubs a little friction material off the pad against the disc. Most pads carry a small metal tab that touches the disc when the material is nearly gone, and that tab is the squeal. It is designed to be annoying, because it is your notice period. Some vehicles use an electronic sensor instead and show a warning light. Motorcycle pads often have a wear groove or line moulded into the material instead of a tab; when the groove is gone, so is the pad.
Grinding is different. A harsh metallic grind on braking means the friction material is gone and the pad's steel backing is cutting into the disc. Stopping distances grow, the disc is being destroyed, and the repair bill is growing with every stop. Drive gently to a shop or have the vehicle collected; this is not a "next month" job.
A pedal or lever that pulses under braking, or a steering wheel that shudders when slowing from speed, points to a disc that is no longer flat, usually from overheating. It can often be machined once; otherwise it is replaced in pairs. A pedal that feels soft or sinks slowly, or a lever that comes back to the grip, is never "just how it feels". It means air or moisture in the system or a leak, and it needs looking at today.
Why fluid has a time limit: brake fluid absorbs moisture from the air through the hoses and seals. After a couple of years it can hold enough water to boil under hard braking, and boiling fluid turns into vapour that compresses, which is the moment the pedal goes to the floor. Water also corrodes the pistons and lines from the inside. Because moisture creeps in whether you drive or not, the interval is measured in years, not distance. The same applies to hydraulic brakes on motorcycles, ATVs and bicycles, and to the hydraulic clutch on many of them. Trailers with hydraulic surge brakes have a reservoir too, and it is the one everybody forgets.
Check it yourself:
- Look through the wheel spokes with a flashlight. On many vehicles you can see the pad's friction material against the disc. New pads are roughly 10 to 12 mm (about half an inch) thick; most manufacturers call for replacement around 3 mm (an eighth of an inch). Check the inside pad too, as it often wears faster.
- Listen with the windows down and the radio off. Squeal on light braking means the wear tab; grinding means stop; a clunk means something loose.
- Open the hood and find the fluid reservoir. Fresh fluid is nearly clear or light amber. Dark brown fluid is due for a change regardless of the date. A level that keeps falling means a leak or very worn pads, since the fluid follows the pistons out as the pads thin.
- Test the pedal when parked. Press firmly and hold for thirty seconds; it should stay put. A pedal that keeps sinking needs a shop.
- Check the drums. Many trailers, older vehicles and some rear axles still use drum brakes; the shoes are hidden, so they need a periodic inspection instead of a glance.
Log the pad thickness on each axle whenever the wheels are off for a rotation or a tire change, and the date of every fluid change. After two or three entries the wear rate is visible in the timeline, and "when will the brakes need doing" becomes a date you can plan around rather than a noise you react to.
Sep 22, 2026