Here Is How To Increase Vacuum For Power Brakes

Here Is How To Increase Vacuum For Power Brakes

Power braking systems are hydraulic brakes that have replaced mechanical brake systems. They use hydraulics to slow down or stop a vehicle.

This hydraulic system involves the use of pistons and cylinders. The cylinder contains fluid, and the system transmits power through the pressure generated in the fluid. Power brakes multiply the force applied to the pedal using mechanical components.

The vacuum booster is one such method. It connects to the pedal and opens up a poppet valve which allows air inflow. This air inflow exerts further pressure on the piston, thereby increasing the pressure on the cylinder.

This article highlights how you can increase vacuum for power brakes, and more. Keep reading to know how.  

How to Increase Vacuum for Power Brakes

The amount of vacuum is a function of the cam and tuning of the engine. For example, power brakes need at least 16 to 18 inches of vacuum to function correctly.

A larger cam usually doesn’t allow for a large enough vacuum for the power brakes, even though it gives that engine revving sound that we love. So, how can we still get at least 18″ of vacuum with a large cam? You can use a vacuum pump and a canister. 

Fortunately, we now have vacuum pumps in the market that can tell how much vacuum you need and deliver it when needed. Consequently, these vacuum pumps don’t require canisters.

The Power Brake System Structure 

The power brake comprises three major sections with different components working towards achieving unique goals necessary to attaining retardation of velocity.

The sections are:

  • the pedal, 
  • the vacuum-assist chamber, and 
  • the master cylinder and piston combination.

The pedal connects to the vacuum assist chamber. The vacuum assist chamber had two sections, restricted by a plate. 

Atmospheric pressure separates the plate from a ram at the pedal end when the brake system is inactive.  Seals help to prevent the loss of this pressure from the chamber.

The plate also connects to the piston on the other end, where two springs hold them in place. Note that a hole present in the metal plate allows for atmospheric pressure in the pedal end.

This atmospheric pressure is a result of air taken from the inlet manifold at the piston end. It becomes sealed off if the brake system is active; we see how this works later.

Apart from the vacuum chamber, we have the piston and cylinder arrangement, which applies pressure to the brake fluid in the cylinder.

These components work in tandem to make up the power brake system. But, first, let’s see a detailed description of the working principles of some of the significant components.

Significant Components of The Power Brake

The vacuum chamber:

Engineers invented the vacuum chamber in 1927 to allow for shorter braking distances. It Increases the amount of force applied by the driver on the pedal on the piston.

The ram at the pedal end pushes towards the plate described above. The plate, in turn, goes against the piston.

The master cylinder:

The master cylinder usually nestles behind the dashboard on the driver’s side. It connects to the vacuum chamber by the piston.

It contains the brake fluid, which drives into the brake lines to the brake calipers by the piston’s prompt. A reservoir mounted above the master cylinder replenishes the brake fluid.

Brake calipers:

This component is unique to disk brakes. It comprises one or two hollow steel pistons, which could be aluminum or chrome-plated. 

It works on the principle of friction. Pressure from the master cylinder propels the piston against metal disks called rotors, which in turn cause the car wheels to slow down.

Drum brake:

The drum brake connects to the master cylinder via another smaller cylinder. The master cylinder transfers pressure to the drum brake via brake lines.

This pressure activates the piston in the cylinder, and two brake shoes within the drum expand to make the drum generate friction and slow down the wheel.

How The Power Brake System Works

The driver first steps on the pedal, which then connects with the ram at the pedal end of the vacuum chamber. This ram then moves forward and breaks the seal. 

This opening allows for outflow of the atmospheric pressure in the pedal end, creating a vacuum.

The ram, when it moves, not only connects with the plate but also seals the inlet for the air into the pedal end. When it connects with the plate, it compresses the springs and puts pressure on the piston, which inputs pressure on the brake fluid. 

This pressure moves to the wheels and causes the vehicle to slow down or stop. The mode of brake power transmission to the wheels varies depending on the car.

Some vehicles use disc brake mechanisms, while others use drum brake mechanisms, all connected to the power brake system.

Disc Brake

The disc brake uses calipers to press what we call brake pads against a disk or rotor. The resulting friction slows down or puts an end to the rotation,  depending on the pressure applied.

The pressure, as discussed previously, comes from the master cylinder, passing through the brake lines.

Definition of Some Disc Brake Terms

Rotor: This is the rotating component of the wheel brake assembly. Brake pads mount sturdily on this component. 

The rotor design depends on the type of vehicle ranging from unique designs for bicycles to heavy trucks. The rotor is usually designed with gray iron.

Caliper: Calipers hold the brake pad and pistons together. They can either be floating or fixed. Fixed calipers are usually more expensive and complex. They do not move relative to the rotor. The design of floating calipers, also called sliding calipers, enables them to move relative to the disk.

Brake Pads: These are pressed against the rotor by the pistons. They can maintain high levels of friction. Due to the role they play, they are subject to wear. The mode of this wear can be adhesive or abrasive, depending on the material used. 

Because of this, brake pads require regular replacement. However, they give the driver some notice when they are due for a replacement. The signal can be in the form of squeals from the tires when the pad has become thin.

Drum Brake

When actuated by pressure from the master cylinder, a drum brake causes shoes or pads to push against a rotating cylinder called a brake drum. But, first, let’s consider some of its components.

Components of Drum Brake

Backing plate: This houses other materials and protects them from foreign materials like dust and debris. All the actions exert pressure on the backing plate, and as such, it needs to be made of solid and durable material.

Brake drum: This component rotates with the wheel and axle. It comprises a type of cast iron that allows for heat transfer and resists wear. When the driver steps on the brake, the shoes or pads push against it with enough force to cause it to slow down.

Brake shoe: The brake shoe consists of two metals welded together. Adhesives keep the material that stays in contact with the drum.

We have looked at some of the types of power brakes, including how to increase the vacuum. Let’s now look at some of the signs of a faulty brake booster.

Signs of a Bad Brake Booster

Stiff brake pedal: The vacuum chamber or brake booster multiplies the force you apply on the pedal and, as such, reduces the effort needed to use the breaks. If your pedal becomes stiff, it is an indication of the brake booster failure.

Short distance brake failure: The invention of the brake booster sought to reduce braking distance. If it takes longer for the brakes to take effect, there might be something wrong with your brake booster.

High brake pedal position: If you observe that your brake pedal can no longer move as much as it used to or takes longer to get back to its default position, the vacuum booster is likely not working correctly.

Now that we have seen the signs, let’s look at a simple DIY method to check for vacuum booster failure.

How To Check If Your Brake Booster Is Bad

Being able to detect these signs is very important to driver safety. Check for brake booster failure using the steps below:

  • Turn of your vehicle’s engine.
  • Step on the brakes the way you would like you are trying to rev an engine.
  • The brake pedal should get stiffer with every instance.
  • It would get to the point when you can’t push it forward anymore.
  • Apply a little pressure to the pedal in an attempt to take it on.
  • Startup the engine; the brake pedal should move forward.
  • If the brake pedal doesn’t move forward, then your vacuum brake booster has failed.


The power brake is a brake that uses hydraulics and mechanical components to transmit pressure. The vacuum booster multiplies the effect of the force we apply on the pedal on the vehicle system allowing for reduced effort and shorter braking distances.

Most vehicles need at least 16″ to 18″ of vacuum. The amount of vacuum is a function of cam size and engine tuning; the more significant the cam, the smaller the void.

You can boost the amount of vacuum using a pump. Some pumps can now detect how much vacuum the system needs and deliver it when necessary.


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