TOYOTA

Single reservoir: One reservoir is used to supply both the front and rear brakes with a specified amount of fluid. When a failure happens, pressure on all four brakes can be disrupted, leading to massive loss.

Dual reservoir: The dual reservoir or dual circuit master cylinder feeds the front and rear brakes separately. One reservoir section supplies fluid to the front brakes, while the other goes to the rear. This fluid is provided through separate brake lines. If one section of the braking system fails, it shouldn't affect both the front and rear brakes with this design.

• When you step on the brake pedal, hydraulic pressure is amplified and then transmitted through the brake lines to each wheel, brake calipers in the front and auto brake wheel cylinder in the rear, at least for vehicles built with rear drum brakes.

• The auto brake wheel cylinders convert that hydraulic brake pressure into movement, tiny pistons expanding and pushing the brake shoes into the brake drum. Moved by the auto brake wheel cylinders, the brake shoes can only expand so far, forcing the friction material into the drums to slow and stop their movement, and therefore, the movement of the wheels attached to them.

• Because the auto brake wheel cylinders are hidden inside the brake drums, they're well-protected, but any failure would also be hidden. Auto brake wheel cylinders are not prone to failure, but they can leak brake fluid if their seals fail. If brake fluid leaks from one of the auto brake wheel cylinders, it would most likely contaminate the friction surfaces of the brake shoes, ruining them and severely reducing braking efficiency.

• While auto brake wheel cylinders do not account for much braking, usually around 30%, they do much for the stability of your vehicle while driving and braking in many situations. Poor rear braking could cause problems with front brakes, as well, forcing them to take more of the braking load, >90% instead of 70% for example, leading to overheating, brake fade, and possible warping.