AfterMarketNews Brake&Frontend BodyShopBusiness Counterman EngineBuilder Fleet Equipment ImportCar Motorcycle & Powersports News Servicio Automotriz Shop Owner Tire Review Tech Shop Tomorrow's Tech Underhood Service Speedville

Preventive Maintenance Profits: Preferred Automotive, Jenkintown, PA

With the summer months heating up and cross-country road trips beginning, many people want to make sure their vehicles are prepped for the long haul. For the first-ever July edition of Maintenance Chronicles, we will focus on Preferred Automotive Specialists,...

Read more...

GM HVAC Door Actuator Motors: Operation And Calibration

GM Electrically Driven Actuator Motors Long gone are the cables and rods jutting out of the firewall to operate the heater control valve or a vacuum unit pulling a blend door open. These days, it’s electrically driven actuator motors (modules) accomplishing...

Read more...

Solving Carbon Deposits In Direct Fuel Injection Engines

Symptom: Misfire codes, stumbling and suspicious fuel trim numbers. On a scan tool, the engine may show a loss in volumetric efficiency. The driver may complain about a loss of power, poor fuel economy and hard starts. Cause: Carbon deposits on...

Read more...

Making Sense Of Steering Angle Sensor Input And Data

Measuring the­ ­position angle, rate of turn and force of the steering wheel is critical for Electronic Stability Control (ESC) systems. Scan tools call these Steering Angle Sensors (SAS) and typically display the information in degrees. The SAS...

Read more...

Rotor Failure: Why Rotors Crack And Make Noise

The prices of rotors seem to be dropping the past few years. Call just about any parts supplier and they can quote you a vast range of prices for the same application. And when you compare the rotors side-by-side, they may look the same, but the difference...

Read more...

Tire Tread Wear: Causes And Symptoms

Understanding Tire Tread Wear Tire tread wear can tell you a lot about a suspension. Most specifically, it can tell you if the angles, inflation and components are within specification. Here are the most common tread wear patterns and what causes them. Over-inflated...

Read more...

The Ins And Outs Of Sanders

Sanders are required tools in today’s collision repair shop. Body techs and painters rely upon them every day to achieve that perfect finish on your customers’ vehicles. Whether you’re prepping a panel for paint or removing imperfections before...

Read more...

Are You Regularly Maintaining Your Equipment?

Technicians who are idling because the welder won’t feed wire, the hydraulic ram won’t pull chains, the booth heater won’t heat or the air compressor won’t compress enough air is a costly mistake, as labor time is the most expensive thing in any...

Read more...

Celebrate 'Back To The Future' Day By Watching The Time Machine Get A 2015 Detail

    For many today is just another Wednesday, but for a lot of people it is more than just your average Wednesday, it is "Back to the Future" Day. It is a day that everyone who watched the cult classic trilogy Back to the Future recognizes...

Read more...


Home European Basic Brake Hydraulics: Classic Symptoms of a Failing Master Cylinder

Print Print Email Email

Anyone who works on brakes should be familiar with basic hydraulics and the various components that make up the hydraulic portion of the brake system. So if you’re not as familiar with this subject as you should be, keep reading and we’ll refresh your memory.

We’ll start at the heart of the system, which is the master cylinder. It converts the force exerted on the brake pedal by the vehicle’s driver into hydraulic pressure to apply the brakes. Depressing the brake pedal moves a push rod in the master cylinder. Mounted on the push rod are a pair of pistons (primary and secondary) in tandem (one after the other) to push against the fluid in the master cylinder bore. This creates pressure that displaces fluid since it’s incompressible. As fluid is pushed from the master cylinder, it exerts pressure through the brake lines to apply each of the brakes.

When the brake pedal is released, the spring-loaded piston assembly in the master cylinder returns to its rest position. The fluid that was displaced by the pistons is pushed back to the master cylinder as the disc brake pads kick out away from the rotors, and the springs inside the drums retract the brake shoes. The fluid returns to the fluid reservoir through the “compensating ports,” which are small openings between the master cylinder bore and fluid reservoir just ahead of each of the pistons.

Master cylinders are divided into two separate hydraulic circuits, with each having its own fluid reservoir and piston. It’s a safety requirement so that if a leak occurs in one circuit, it won’t affect the other circuit, leaving at least two brakes operational to stop the vehicle. With most rear-wheel-drive (RWD) vehicles, the hydraulic system is divided front to rear with one circuit for the front brakes and a second circuit for the rear brakes. On many front-wheel-drive (FWD) cars, the brake system is split diagonally. The left front and right rear brakes share one circuit, while the right front and left rear brakes share the other.

The most common problems that occur in the master cylinder is wear in the piston bore and piston seal failure. The classic symptom of a failing master cylinder is a brake pedal that slowly sinks while pressure is held against the pedal. The cure is to replace the master cylinder.

BRAKE LINES & HOSE
The arteries of the brake system are the steel lines and flexible rubber hose that route hydraulic pressure to each brake when the driver steps on the brake pedal. The lines and hose must withstand pressures that can range from a few hundred pounds per square inch up to almost 2,000 psi! If a line or hose can’t take the pressure and blows, all braking ability in the affected brake circuit will be lost.

A slow leak in a brake line or hose is almost as bad as a sudden failure because, over time, enough fluid may be lost to allow air to enter the hydraulic system. Air in the fluid is bad because air is compressible. This increases the amount of pedal travel that’s necessary to apply the brakes, and may increase it to the point where the pedal hits the floor before the brakes apply.

The first indication of a leak in a brake line or hose may be a low fluid level in the master cylinder reservoir. Other clues may include wet spots on the driveway, dampness on the back of a drum brake, or a brake warning light that comes on. If a leak is suspected, the entire brake system should be inspected to find the leak.

The most likely leak points are the brake calipers, wheel cylinders and rubber brake hoses, though steel lines can also rust through and leak. Rubber brake hoses also need to be inspected for age cracks, bulges, swelling or other damage that would indicate a need for replacement. Rubber hoses have an expansion-resistant inner lining that should not give under pressure. If the inner liner leaks, fluid will force its way under the outer liner causing a bubble or blister to appear when the brakes are applied.

Although it doesn’t happen very often, sometimes internal damage or deterioration in a rubber hose allows a small flap of material to lift up and plug the line. This prevents brake pressure from reaching the wheel, causing a brake pull when the brakes are applied.

The same thing can also happen to steel brake lines. Debris in the brake fluid, or a crushed or kinked line, can block the passage of hydraulic pressure to the brakes. In some cases, pressure will get through, but when the brakes are released, the blockage prevents pressure from releasing back to the master cylinder causing the brake to drag.

Replacement hose must be the same length as the original, with the same type of end fittings. A hose that is too long may rub against a suspension component or other parts, while a hose that’s too short may be stretched and damaged when turning or by excessive suspension travel.

Pages: 1 2Next page

The following two tabs change content below.
Larry Carley

Larry Carley

Larry Carley has more than 30 years of experience in the automotive aftermarket, including experience as an ASE-certified technician, and has won numerous awards for his articles. He has written 12 automotive-related books and developed automotive training software, available at www.carleysoftware.com.
Larry Carley

Latest posts by Larry Carley (see all)

  • GLJSD

    My son changed his front caliper on his 2003 tiburon. He then tried to bleed the brakes, then I came to help. We have solid jets of fluid at all four wheels, we even loosened the lines at the master cylinder one at a time to bleed it there. We kept the reservoir above the minimum, and kept refilling as we were bleeding. Despite all this, the pedal goes practically to the floor and there is no real braking power. The car has 100,000 miles. Do you think it’s the master cylinder? The brakes appeared ok before changing that leaky caliper.

    • GLJSD

      Ok, they sold my son the caliper for the passenger side instead of the driver’s side. Therefore, the nipple was on the bottom. There must have been air in the caliper and it wasn’t able to bleed.

Latest articles from our other sites:

Ford Focus: Wet Carpet On Passenger Side

Models 2012-2013 Focus ISSUE Some 2012-2013 Focus vehicles built on or before 11/12/2012 may exhibit wet carpet on the passenger-side front foot well. This is likely due to leaking climate control...More

Bosch's 'Giving Track' Contributions This Season Reach $20,000

When Denny Hamlin took the checkered flag at the Federated Auto Parts 400 on Sept. 10 in his Bosch-equipped No. 11 FedEx Ground Toyota, Bosch crossed the $20,000 mark in charitable contributions through...More

ASA To Host Largest Regional Education Program Of 2016 During AAPEX

The Automotive Service Association (ASA) announced a strategic partnership with the Automotive Aftermarket Products Expo (AAPEX), which is co-owned by Auto Care Association and Automotive Aftermarket Suppliers...More

Centric Announces New StopTech Brake Components For 1989-2016 Mazda Miatas

Centric Parts has introduced a comprehensive new program of StopTech Brake Kits and Components for the 1989-2016 Mazda MX-5 Miata. The program covers all model year Miata/MX-5 variations and supplements...More

Ernst Offers Optimum Solution for Socket Storage

The Socket Boss from Ernst Manufacturing, Inc. is extremely versatile, handling three drive sizes and having the option of adding socket clips and ratchet and extension holders. Each socket rail has...More

Bartec Announces Increased Placard Coverage for Tech400Pro

Bartec USA announces the addition of 23 vehicles whereby the Tech400Pro and Tech500 can adjust the recommended inflation pressure [RIP or placard]. Seven of these additions are brand new, never offered...More