Any brake problem is serious and needs immediate attention. Sticking, dragging or binding brakes all describe the same problem, a brake that’s not fully releasing.
So, why do car brakes smoke? The 8 most common causes of car brake smoke, includes:
- Sticking brake pads
- Seized caliper floating pins
- Seized brake caliper piston
- Excessive brake rotor rust
- Overfull brake fluid reservoir
- Perished flexi brake hose
- Over-adjusted handbrake cable (rear)
- Brake shoes failure (rear)
By the end of this post, you’ll understand why car brakes smoke. You’ll also learn how to diagnose and fix them.
1 What Are Sticking Brake Pads?
The brake pads as you may know are what slow and stop your car. The pads are pushed against metal rotors by the brake caliper piston. The pads are made from a soft material designed to wear down without causing excessive wear to the metal rotors.
When the pads are in the rest position, they are just millimeters away from the rotor.
The pads sit on the carrier on rails, and the rails allow the pads to move against the rotors as the brake caliper piston pushes on them.
The rail and the brake pad backing are made from metal. Over time, rust, brake dust, and debris get caught between the rail and pad, as you can imagine, prevents the pads from moving freely.
Light build-up of debris in the rails can cause brake noise, but when it gets heavier it can cause the brakes to drag, excessive brake dust on the wheel, and as you know heat and smoke.
The fix is to remove the pads, clean the rails using a wire brush and apply some copper grease before replacing the pads.
Old, corroded, disintegrated, or damaged pads will, without doubt, cause the brakes to drag.
2 What Is A Seized Brake Caliper Pin?
The caliper is anchored to the brake carrier by two sliding bolts/pins. Most cars old and new use this type of brake set up. It’s known as a floating caliper.
It’s so-called because it has the ability to move freely across the brake carrier. It uses the sliding pins top and bottom to hold the caliper in place.
The caliper bolts slide into cylinders in the carrier and are then bolted to the caliper itself. The bolts have a rubber boot that prevents moisture and debris from entering the cylinder, often the rubber boot will tear or come loose allowing moisture in and rust to form. You’ve guessed it, pretty soon you’ve got a seized caliper.
When the sliding pins seize of the caliper seize, often you’ll hear a creaking sound from the brakes proportional to how hard you press them. This is a sure sign of seized pads or pins.
Fixing seized sliding pins can be hit and miss. Often they’ll be frozen into the carrier solid. In some cases, I’ve had to replace the carrier and the pins.
If however, you can get them out, go ahead and clean them, use a wire wheel to remove the rust. When installing, I use silicone grease on the pins, it prevents the rubber components like bushings and boots from swelling.
3 What Is A Seized Brake Caliper Piston?
The caliper houses the piston, and the piston is what pushes the pads against the rotors. So this is the business end of the brakes. Without the piston moving, nothings going to happen.
Apply the foot brake and the brake fluid pressure pushes the piston out which forces the pads against the rotors, slowing the car down.
As you release the brakes the piston moves back a few milometers allowing free wheel movement again. A seized caliper will only move outwards, it won’t retract by very much as you lift off the brakes and so the wheel brake is still applied slightly.
So why does the piston seize?
Usually, because the piston or caliper cylinder has corrosion. Corrosion is caused by moisture in the brake fluid.
Brake fluid is hygroscopic, it means it attracts moisture from the atmosphere, and moisture on metal means rust.
There are two fluid types Glycol and Silicone, mixing them can cause brake problems. Brake fluid should be changed every 3 years unless your car uses DOT 5 which is silicone-based and lasts years longer. Use whatever type is marked on your brake fluid reservoir cap.
4 Excessive Brake Rotor Rust
This is a problem well-known to classic car owners. Cars that lay up especially outdoors in damp climates develop problems with excessive rust on the calipers. The best solution is to drive the car more often, but if that isn’t an option, store your car indoors in a heated area preferably.
Excessive rust on the rotors is usually fixed by just driving the car and braking gently to help clear the corrosion. If it’s too bad, however, replacement rotors and pads may be needed.
If your rotors are within spec a good repair shop will turn them on a lathe which will be less expensive.
If you need brake system repair tools, check out the “Brake repair tools page”.
You may find the brake resources page useful, it’s a fluff-free guide to DIY brake repairs.
5 Over Full Brake Fluid Reservoir
This is not very common but overfilling your brake fluid does happen. All reservoirs will have a max and min level.
Brake fluid heats as you use the brakes, and heated brake fluid expands slightly, if the expanded fluid has nowhere to go it will push the brake pistons out to relieve the pressure.
It’s an unusual one because the driver will only have the problem when the brakes and fluid get really hot but worth checking just the same.
If your fluid looks like the pic above, it is best to think about fluid flush.
6 Perished Flexi Brake Hose
This is an unusual one too, but still worth knowing. As the rubber flexible hoses get old they start to break down, but not just on the outside.
The inside walls start to peel away and start to act as a kind of one-way valve. As you push the brake pedal, the fluid is forced past the blockage but when you release the pedal, the rubber debris blocks the returning fluids’ passage. The result is a dragging brake.
The fix here is to replace all the flexi brake hoses and change the fluid.
7 Over Adjusted Hand Brake Cable
A hand brake that is too tight may not cause the wheel to drag when the car is cold but does when the car has traveled several miles. The reason for this is the metal components expand with heat causing the brakes to rub.
The fix is simple, drive the car to heat the brakes and back off the handbrake adjuster a turn, and test.
Older cars will have drum brakes at the rear, and newer models will have calipers that either have a handbrake lever assembly or a mini drum brake set up inside the disk brake.
8 Brake Shoe Failures That Cause Smoke
Brake shoes are fitted inside brake drums. Drum brakes were once fitted to all cars front and back. Cars then evolved to have calipers at the front and drums at the rear and today nearly all cars run calipers all around.
Brake shoes are a wearing part just like brake pads. They are larger in size and are more complicated to replace. They are held in place with clips and springs, a wheel cylinder is used to apply force to the shoes causing them to push on the brake drum slowing the car.
Any of these issues can cause drum brakes to stick and cause smoke:
- Leaking wheel cylinder
- Shoes linings coming away
- Retaining clips breaking causing binding
- Springs breaking causing binding
- Warped drum
A complete rear brake job includes turning the drums or replacing, new shoes, new brake cylinder, and fresh brake fluid.
Diagnosing Which Wheel Is Dragging
Symptoms of a dragging brake include smoke as you know, but for some, it may not be that obvious. Other less dramatic symptoms include lots of brake dust and the wheel that’s dragging will be hotter than the rest.
When driving the vehicle, the steering will pull towards the dragging brake side. The vehicle will be hard on the gas and it won’t coast down hills like normal.
After you park the car you’ll hear the brakes make unusual ticking noises as the metal components start to cool down.
A sticking brake can cause other problems such as warp the rotor, damage ball-joint boots, wheel bearings, and ABS sensors apart from the risk of setting your car on fire or completely locking up the wheel on the highway.
Preventing Brake Problems
You can prevent these types of problems by having a brake check twice a year.
Complete brake inspection includes:
- Pads / shoes should be checked for wear
- Rotors and drum run out checked
- Handbrake adjusted
- Brake lines inspected for corrosion and flexi brake hoses checked for cracking or cuts
- Wheel cylinders checked
- Brake fluid flushed every three years
Can you drive with a stuck caliper? While it is possible to drive with a partially stuck caliper, it’s not advised, at highway speeds the wheel could lock causing the car to skid uncontrollably.
Can you change just one caliper? Yes, you can change just one brake caliper, but it is better to replace both together. The new brake caliper will be more efficient and that can lead to a brake imbalance.
- About the Author
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John Cunningham is an Automotive Technician and writer on Rustyautos.com. He’s been a mechanic for over twenty-five years and has worked for GM, Volvo, Volkswagen, Land Rover, and Jaguar dealerships.
John uses his know-how and experience to write fluff-free articles that help fellow gearheads with all aspects of vehicle ownership, including maintenance, repair, and troubleshooting.