A sticking brake caliper is one of those faults that creeps up slowly. The car feels a bit sluggish, one wheel seems dirtier than the others, and then one day you notice a hot, burning smell after a drive.
It's worth fixing quickly. A caliper that won't release wears out pads and discs, overheats the brake and can make the car pull to one side. Here's how to spot it, what causes it and what to do.
What a brake caliper does
The caliper is the part that squeezes the brake pads against the disc when you press the pedal. Inside are one or more pistons pushed out by brake fluid. On most cars, the caliper also slides on two guide pins so it can centre itself over the disc.
When you take your foot off the brake, the piston should pull back slightly and the caliper should slide freely, so the pads stop pressing on the disc. A sticking caliper doesn't release properly, so the pads keep rubbing.
Symptoms of a sticking caliper
- The car pulls to one side while driving, or when braking
- A burning smell after driving, often from one wheel
- One wheel much hotter than the others after a drive
- Much more brake dust on one wheel than the other
- The car feels sluggish, as if the handbrake is partly on
- Squealing or grinding from one corner
- Fuel economy getting worse
- Uneven wear, with one pad much thinner than the other
A quick check you can do
After a normal drive, park safely and carefully hold the back of your hand near each wheel, without touching. A sticking brake will usually feel noticeably hotter than the others. Take care, as discs and calipers can be hot enough to burn.
With the car safely raised on axle stands and the handbrake off, you can also try turning each wheel by hand. A wheel that's much harder to turn than the one on the other side suggests a binding brake. Front wheels on front-wheel-drive cars will feel a bit stiffer because of the drivetrain, so compare left with right.
What causes a caliper to stick
Seized slide pins
This is the most common cause. The guide pins the caliper slides on are greased and protected by rubber boots. If a boot splits, water gets in, the grease washes out and the pin rusts. The caliper can't slide, so one pad stays in contact with the disc.
A corroded piston
The piston is protected by a rubber dust boot. If that splits, dirt and moisture get behind it and the piston can corrode and stick in its bore.
A collapsed brake hose
Flexible brake hoses can break down inside with age. Sometimes they act like a one-way valve, letting fluid in to apply the brake but not letting it back out to release it.
Sticking handbrake mechanism
On rear calipers with a built-in handbrake, the mechanism or cable can seize, holding the brake on. Electronic parking brakes can also develop faults.
Lack of use
Cars that are parked for long periods, especially through winter, are more prone to sticking calipers, because the pins and pistons have time to corrode.
Is it safe to drive?
A sticking caliper shouldn't be ignored. It can overheat the brakes, boil the brake fluid and cause the car to pull unexpectedly. In severe cases, the brake can drag so hard that the wheel gets very hot. If you notice the symptoms, get it checked soon and avoid long journeys until it's fixed.
Repair or replace?
If the cause is seized slide pins, cleaning them and fitting new pins and boots with fresh high-temperature grease is often enough. Caliper repair kits with new seals and boots are available for many cars.
If the piston is badly corroded, the bore is pitted or the caliper has been leaking, replacing the caliper is usually the better option. Replace calipers in pairs across an axle if they're of a similar age, so the braking stays even.
A dragging brake usually wears the pads and discs on that side too, so check them while everything is apart. Our guide to worn brake discs and pads shows what to look for. If you've noticed squealing, our guide to squeaky brakes may help too.
After fitting a new caliper, the system needs bleeding to remove air.
Finding the right caliper
Calipers are specific to the car, the axle and the side, and some models have different brake sizes depending on the engine. The safest way to get the right one is to match the part number on your old caliper, or the OEM number. If you're not sure, send us your VIN and we'll help you find the right one.
We stock a range of brake calipers as well as discs, pads and other brake parts for most popular makes.
This article is a general guide only. Brakes are a safety-critical system. If you're not confident working on them, have them checked by a qualified mechanic.