Pressing the brakes requires a surprising amount of effort; anyone who ever coasted a car with a stalled engine and pulled it to a halt will immediately understand the value of a brake booster.
A brake booster is an assembly designed to reduce brake pedal effort, thereby boosting brake performance and increasing driver comfort.
The brake booster is known by a few different names; some include – Power brakes, Power brake booster, Brake vacuum, Vacuum booster, Servo brakes, and Servo assisted brakes. Although the name brake booster means the same thing, not all boosters are the same.
A booster needs a power source, and it’s the type of power it uses that makes boosters different.
There are three main flavors of brake boosters and some variations of each.
The main types are:
- The Vacuum booster – powered by a vacuum
- The Hydro booster – powered by fluid pressure
- IBC – powered by computers (witchcraft)
We’ll look at the most common brake booster type first, the Vacuum booster.
What’s Vacuum-Assisted Brakes?
Vacuum-assisted brakes mean the driver’s effort on the brake pedal is multiplied by manipulating the vacuum inside a cylinder. The brake servo cylinder employs a diaphragm and a valve to create a low-pressure compartment to which the brake pedal rod is attached.
Pressing the brake pedal sucks the brake rod further into the low-pressure void, thereby boosting brake force.
But where does the vacuum come from? In gas-powered engines, vacuum is a naturally occurring resource created by the downward moving pistons.
A modification is needed to diesel engines as they aren’t as giveish with engine vacuum and so in these models, a mechanical pump is generally fitted to the camshaft to create the needed vacuum.
The vacuum is supplied to the servo by means of a hard plastic hose.
What’s Hydro Assisted Brakes
Hydro-assisted brakes use scavenged hydraulic power, usually from the power steering pump to assist brake pedal application.
The hydro assembly is fitted between the master cylinder and the brake pedal. When the brake pedal is pressed, the attached spool valve located inside the hydro body causes proportional fluid pressure push on the rod piston to assist brake activation.
Integrated Brake Control (master cylinder and assistance) is the latest and greatest evolution; it’s an electro-mechanical brake system, a fly-by-wire type system with a mechanical fail-safe system in the background. It’s lighter, smarter, and less bulky than a traditional Master cylinder and Servo assembly.
It employs brake pedal mounted sensors to detect pressure and speed of brake pedal use, and the computer interprets our commands and applies the correct brake force – no servo needed.
This type of system is perfect for Hybrid, EVs, and autonomous cars where more computer control is needed for safety, brake regen, etc.
Where’s a Brake Booster Located?
Brake boosters, no matter which type you have, are located under the hood at the firewall directly behind the brake pedal assembly (most models).
Where’s the Vacuum Type Booster Located?
The vacuum type is easy to identify since it is a large disc-shaped cylinder to which you’ll find a vacuum hose attached. In addition, the master cylinder with brake fluid reservoir is fastened to it.
Where’s Hydro Type Booster Located?
The hydro type booster is less obvious as it is smaller than the Vacuum type, but nonetheless, you’ll have no difficulty identifying it by the relatively speaking large power steering pipe fittings feeding the booster.
Where’s Hydro Type Booster Located?
The IBC is located under the hood on the firewall just behind the brake pedal assembly.
Brake Booster Problems
Brake boosters don’t really give a ton of issues, no matter which type you have.
Vacuum Brake Problems
Servos are built tough and rarely go bad, but when they do, it’s likely the inner rubber diaphragm or valve.
Hydro Brake Problems
Hydro scavenge power from the power steering, and so any issue there will obviously cause issues downstream with brake performance. Typical hydro power brake assembly issues include leaking seals and worn spool valves.
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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.