Causes Of Hissing Brake Sound In Your Truck

Hissing is mainly associated with snakes and cats sometimes, but your truck’s brakes can produce this sound. When you start experiencing a hissing brake sound is an indication of a mechanical problem worth not ignoring. Even though you should not ignore it, it is an issue that is easy to fix. A professional mechanic should check the cause of the hissing sound from your brakes, but you can also do it if you are good at DIY mechanics.

Causes of the Hissing Brake Sound

There are significant and minor causes of the hissing brake sound. Faulty brake booster and master cylinder are the common causes, while the missing silencer, damaged vacuum booster, or leaking vacuum hose are the minor causes. Here are the causes of hissing brake sound worth knowing.

Faulty Brake Booster

When your pedal produces, a hissing sound indicates that the brake booster is faulty. The primary role of the brake booster is to multiply the pressure you apply when pressing the brake pedal. When it does its role effectively, the slight pressure you apply multiplies to a significant force to slow down your truck. The brake booster relies on hydraulic fluid to perform this role. 

You will experience these signs when your brake booster is faulty.

  • Stiff brake pedal.
  • The pedal does not return to its original position whenever you press it.
  • Decrease in RPM when you idle or brake.

When your booster is faulty, it indicates several things are wrong which if ignored, you will experience brake failure. 

Faulty Master Cylinder

The master cylinder transmits pressure generated when you press the brake pedal to the braking mechanism on the wheels. It has a reservoir with brake fluid that sends adequate pressure to the brakes and no air within the system. When faulty, you will note these signs.

  • The brake pedal will be spongy and take time to spring back after the release.
  • Leakages beneath your truck.
  • Uneven brake pad wear. 

Leaking Vacuum Hose

For a brake booster to function effectively, it requires pressure. The vacuum hose transfers pressure from the engine to the booster. In case of leakage, you will hear the hissing sound when braking, and replacing it is the solution.

Faulty Vacuum Booster

If your truck has power brakes, the vacuum booster augments the pressure from the brake pedal to the master cylinder. The vacuum booster contains a diaphragm and a canister that maintains a partial vacuum to enhance braking. When faulty, you cannot determine the pressure necessary for braking, which can lead to an accident. 

Damaged Foam Silencer

It is the least dangerous cause of a hissing sound from your brakes. The brake booster has a foam silencer that acts as a soundproof. If it is faulty or missing, you will hear all the activities within the brake booster. 


The hissing brake sound generally results from a broken brake booster or faulty master cylinder, but when the foam is missing, you do not need to worry because your truck will not be at risk. Other causes besides the missing foam silencer can be dangerous, and you should repair them as soon as possible.

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