There a several ways you may be alerted to a brake fluid leak. The brake fluid warning light might appear on the dashboard, the brake pedal may feel spongy, or it might travel all the way to the floor before working. Alternatively, you might spot a small pool of light coloured thin oil, similar to cooking oil, on the drive or road. Any of these are danger signs and need investigating and fixing immediately.
The first step is to try and diagnose the problem. If the fluid level warning light has appeared on the dashboard, and there are no other signs of a leak, open the bonnet, identify the brake fluid reservoir and remove the top. Check your owner’s manual if you’re unsure where to locate the reservoir. The reservoir should have minimum and maximum lines on it. If the fluid level is within these lines then suspect the level sensor is faulty and may need replacing.
If some fluid has leaked out the level will be below the minimum line and the next step is to identify where the leak is. If some fluid has leaked on to the drive, or road, look under the car in that area first. If there isn’t any obvious leak you will have to inspect the whole system starting with the servo, which is located under the reservoir. The servo acts as a vacuum when you brake to increase the pressure in the system and make braking more effective. Check all around for any leaks. Follow the thin metal pipes from the servo out to the four wheels of the car, all the time looking for any areas that look damp or darker compared to their surroundings. If no leak is immediately obvious then you may have to remove the wheels to inspect the brake callipers or remove the wheels and drums to inspect the brake pistons. It might be possible to turn the steering to inspect the callipers on the front wheels without removing them. Check all around the callipers because the seals in them can often leak and the fluid can fall straight on to the brake pads without the leak being obvious.
Once you have identified the leak it should be a simple case of replacing the part or the pipe. Leaks in pipes frequently occur at joints due to vibration or movement, or in areas where they have rubbed against something else. Rusty pipes can also become thinner over time and eventually the pressure in the system can force a hole in them. The majority of brake pipes are available as spare parts from motor dealers already formed into the correct shape and size and it should be a case of simply removing the damaged section and replacing. Remember to place plenty of newspaper under the area, or better still, an old bowl to catch any fluid that leaks when the pipe is removed. Replacing the top on the reservoir before you start can help reduce this by preventing air from entering the system.
Leaks in brake callipers, or pistons, should be dealt with in a similar way. It is possible to buy kits to recondition them; however, in reality they are usually only marginally cheaper than buying a reconditioned part from a motor dealer. Remove the leaking part, replace with a new one at the same time checking the brake pads or shoes to make sure they have not been contaminated by fluid. If there is any suspicion they have been contaminated they will not work effectively and should also be replaced.
Once the work has been completed the brake system should be bled remove all traces of air otherwise the system will not work effectively. This requires two people. Ensure the fluid level is topped up to maximum. Near each brake calliper or brake piston there will be a bleed nipple. Start at the wheel furthest away from the fluid reservoir. Attach one end of a thin plastic pipe to the bleed nipple and place the other end in an old jar. Ask your assistant to press the brake pedal whilst you loosen the bleed nipple. You should see brake fluid squirt down the tube and in to the jar. Tighten the bleed nipple and ask your assistant to release the pedal. Repeat this several times, checking the fluid level in the reservoir in between, until clear brake fluid without air bubbles flows in to the jar. Repeat the process for the other wheels working from the furthest away from the fluid reservoir to the closest.