speedkar9

I cut open a brake booster and master cylinder from my Corolla to see what’s inside and how it works. I made a short video on the breakdown here:


The brake booster is responsible for multiplying the force that is being applied to the master cylinder. The master cylinder piston will push hydraulic brake fluid out through the brake lines to the drum or disc brakes, slowing the wheels.
Here’s a few photos of the breakdown.
The master cylinder and brake booster assembly is usually mounted on the driver’s side of the car, in the engine bay. Its bolted through the firewall.

Here’s the brake pedal assembly, master cylinder and brake booster removed from the vehicle:

The master cylinder is essentially a piston that pushes hydraulic fluid from the reservoir to the discs/drum brakes

There’s actually two pistons in series in the master cylinder for redundancy:

The float inside the master cylinder operates the brake fluid level warning light through a reed switch. When the magnetic float reaches the bottom the resistance turns to zero as the switch closes, turning the light on the dash.

The back of the brake booster has a dust boot with a small sponge air filter inside. It draws atmospheric air into the booster from under the dash when you step on the pedal.

Inside the booster, chopped open is a big diaphragm. It fills one side with vacuum and the other side with atmospheric air pressure. The pressure differential causes it to push toward the master cylinder, giving you assist.


This valve seals the chamber between the diaphragm. In its rest position, this valve is open, allowing engine vacuum to balance both sides of the diaphragm so its in a neutral state.


And that’s pretty much all the components it takes to stop a 4000lb car with the press of your foot.

mmarshall

Thanks. You did a generally good job of explaining the basics of the system, but (no offense), forgot one important part. Since the late 1960s, Federal regulations have required a split-master-cylinder on all new American-market cars.....although you are in Canada, I believe that your country has the same regulation. That's to guard against total brake failure caused by a leak in the master cylinder....or elsewhere in the system. The master cylinder is split into two main parts (reservoirs). The fluid in each reservoir controls one front brake and one opposite rear brake. That way, if one reservoir leaks fluid, the remaining fluid will operate one front and one rear brake in a manner that should keep the car from swerving, though, in general, except for rear or mid-engined cars, the front brakes usually do a heavier share of the braking load, so the car might (?) swerve a little in that direction. In some cases, the two different reservoirs control both front or rear brakes independently,

Johnhav430

Next lesson...ABS! I've replaced the ABS module and installed it, did the computer bleed then 2 manual bleeds, but I would not be able to tell you how the valves work, and what the computer is doing with them etc. Just accepted it as a unit I suppose...

In retrospect, I went to a salvage yard with my uncle to find one for his A6, we bought one, and it was faulty just like his. Today, I would know it was a bad bet (a $50 bet), and that he should have had his original repaired...

edit this is what I mean, on mine, the motor inside the black casing was faulty, and I did not see these valves because I sent the entire unit out, which includes the computer module (silly me turned the ignition on with the abs pump out of the car, and the car went berserk, you shoulda seen how many fault codes populated). Would be curious how this thing actually worked.