Brake problems can develop gradually, and the first symptom does not always identify the exact cause.
Noise, vibration or a change in pedal feel may be related to normal wear, contamination, incorrect installation, a hydraulic issue or another component within the braking system.
Before replacing any parts, the vehicle should be inspected and the cause properly diagnosed. Components should only be replaced when they are worn, damaged, contaminated or outside the vehicle manufacturer’s specifications.
This guide outlines common brake symptoms and possible causes. It is intended as a starting point for inspection and should not replace professional diagnosis or the vehicle manufacturer’s service procedures.
Low Brake Fluid
Low brake fluid usually indicates a leak in the brake system, which is a serious safety concern.
The calipers, wheel cylinders, brake hoses, brake lines and master cylinder should all be inspected.
If a leak is found, the faulty component must be replaced immediately. The vehicle should not be driven until repairs are completed, as brake fluid loss can lead to complete brake failure.
Low Brake Pedal
A low brake pedal can occur when drum brake adjusters stick and fail to compensate for normal brake shoe wear.
Adjusting the brakes may temporarily restore pedal height. However, if the adjusters are not cleaned, repaired or replaced, the issue may return as the brake shoes wear.
Other possible causes include:
- Worn brake pads or shoes
- Air in the brake system
- A brake fluid leak
- A problem with the master cylinder
Spongy or Soft Brake Pedal
A spongy or soft brake pedal may indicate air in the brake system.
This can be caused by:
- Improper bleeding
- Brake fluid loss
- Low brake fluid
- A brake hose that expands under pressure
The brake system must be properly bled in the correct sequence for the vehicle. The vehicle manufacturer’s service procedures should always be followed.
Excessive Pedal Travel
Excessive pedal travel may be caused by:
- Worn brake pads or shoes
- Misadjusted drum brakes
- Air in the brake lines
- A brake fluid leak
- A problem with the master cylinder
This condition can be dangerous, as the pedal may travel too far before full braking force is achieved. The vehicle should be inspected as soon as possible.
Brake Pedal Sinks to the Floor
A brake pedal that sinks to the floor is a serious safety issue.
It is usually caused by:
- Internal seal failure in the master cylinder
- A hydraulic system leak
- Significant loss of brake fluid
In either case, the brake system may be unable to maintain hydraulic pressure. Do not drive the vehicle until it has been inspected and repaired.
Brake Pedal Pulsation
A pulsating brake pedal is commonly associated with disc thickness variation (DTV).
DTV can develop when there are differences in rotor thickness around the friction surface. Other contributing factors may include:
- Excessive rotor runout
- Uneven friction material deposits
- Rotor overheating
- Contamination between the hub and rotor
- Incorrect wheel lug nut torque
- Worn or damaged wheel bearings
Depending on the condition of the rotor, it may need to be professionally resurfaced or replaced.
Brake rotors must remain within the vehicle manufacturer’s specified limits for thickness, parallelism and runout. As a general reference, many vehicles require rotor faces to remain parallel within approximately 0.0005 in (0.0127 mm) and runout to remain within approximately 0.002 in (0.050 mm). Always confirm the correct specifications for the individual vehicle.
Wheel bearings should also be inspected for excessive play, noise or damage. They should be serviced or replaced according to the vehicle manufacturer’s procedures.
Steering Wheel Vibration
Steering wheel vibration during braking usually indicates torque variation in the brake system.
This is often caused by uneven brake pad material deposits on the rotor surface, resulting in a grab-and-release effect.
The uneven torque is transferred through the steering system and felt at the steering wheel. In some cases, the vibration may also be related to DTV, particularly when it occurs together with brake pedal pulsation.
The brake rotors should be inspected for:
- Uneven friction material deposits
- Dark patches on the rotor surface
- Excessive runout
- Uneven wear
- Heat spots
- Rotor thickness variation
Chatter
Chatter refers to vibration and noise felt through the brake pedal, steering wheel or vehicle during braking.
Possible causes include:
- Improperly machined brake rotors
- Uneven rotor surfaces
- Uneven friction material deposits
- Loose or damaged brake hardware
- Incorrect brake pad fitment
The complete brake assembly should be inspected to identify the source of the vibration or noise.
Scraping Noise
A scraping noise may be caused by contact or vibration between the brake pads, rotor, caliper and related hardware.
Possible causes include:
- Damaged or incorrectly installed brake hardware
- A bent dust shield contacting the rotor
- Debris between the pad and rotor
- Severely scored brake rotors
- Incorrect brake pad fitment
- A seized or damaged caliper component
Depending on the cause, corrective action may include repairing or replacing damaged hardware, replacing the brake pads or resurfacing or replacing the brake rotors.
Brake lubricant or anti-noise compound should only be applied to the specified contact points. It must never be applied to the brake pad friction material or rotor friction surface.
Brake Squeal
Brake squeal is a high-frequency vibration noise caused by movement between the brake pads, rotors and caliper components.
It can sometimes be reduced by ensuring:
- The brake rotors are in suitable condition
- The brake pads are correctly fitted
- Caliper hardware is secure and undamaged
- Shims are correctly installed where required
- Contact points are correctly lubricated
- The brake pads and rotors are properly bedded in
Some brake noise may also be influenced by the brake pad material, vehicle design, operating temperature and driving conditions.
Grabby Brakes
Contamination on the rotor surface can cause uneven braking and a grabbing sensation.
Possible contaminants include:
- Oil
- Grease
- Brake fluid
- Anti-seize compound
- Other workshop chemicals
The source of the contamination must be identified and eliminated. Contaminated brake pads should be replaced, as cleaning may not remove the contamination from the friction material.
Severely scored or damaged brake rotors may also contribute to this condition and may require resurfacing or replacement.
Dragging Brakes
Dragging brakes occur when the brake pads or shoes do not fully release from the rotor or drum after the brake pedal is released.
This can lead to:
- Vehicle pull
- Increased fuel consumption
- Excessive heat buildup
- Accelerated brake wear
- Reduced braking performance
Common causes include:
- Weak or broken return springs in drum brake systems
- A seized caliper piston
- Corroded or sticking caliper slide pins or bushings
- A restricted brake hose
- Incorrectly adjusted drum brakes
- A faulty parking brake mechanism
The affected brake components should be inspected and serviced or replaced as required.
Brakes Pull to One Side
A vehicle that pulls to one side during braking may have a problem with one or more brake components.
Possible causes include:
- Contaminated friction surfaces
- Misadjusted drum brakes
- A faulty wheel cylinder or caliper
- Dragging brakes on one side of the vehicle
- Mismatched brake pad materials
- Differences in rotor condition, thickness or wear
- Uneven tire pressure or tire wear
The brake system, tires, suspension and steering components should all be inspected when diagnosing a vehicle pull.
Hard Brake Pedal
A hard brake pedal usually indicates a lack of brake assist.
On vehicles equipped with a vacuum brake booster, possible causes include:
- Low engine vacuum
- A leaking or disconnected vacuum hose
- A faulty brake booster
- A defective check valve
A basic vacuum-booster test can be performed by switching off the engine, pressing the brake pedal several times to release the vacuum and then holding the pedal down while restarting the engine.
If the pedal sinks slightly when the engine starts, the vacuum booster may be functioning correctly. If the pedal does not move, further inspection of the vacuum system or brake booster is required.
This test does not apply to every vehicle. Electric and hybrid vehicles may use a different brake-assist system and should be diagnosed according to the vehicle manufacturer’s procedures.
Brake Fluid
Brake fluid is hygroscopic, meaning it absorbs moisture over time.
As moisture content increases, the boiling point of the brake fluid can drop. Under heavy braking, this can contribute to vapor formation and reduced braking performance.
Brake fluid should be inspected and replaced according to the vehicle manufacturer’s recommended service interval. The correct fluid type specified for the vehicle must always be used.
When flushing the system, ensure the master cylinder reservoir and surrounding areas are clean before beginning. This helps prevent contamination from being circulated through the brake system.
When Should the Brakes Be Inspected?
Have the braking system inspected if you notice:
- A change in brake pedal feel
- Steering wheel vibration during braking
- Brake pedal pulsation
- Unusual brake noise
- The vehicle pulling to one side
- A brake warning light
- Low brake fluid
- A burning smell or excessive heat from a wheel
- Reduced braking performance
If the brake pedal sinks to the floor, brake fluid is leaking or braking performance is significantly reduced, do not drive the vehicle. Have it inspected and repaired by a qualified technician.
This information is provided as a general guide only. Always follow the vehicle manufacturer’s service procedures and specifications.