Of all the type of fluid used in a car, the most important is brake fluid. It is what keeps us and our loved ones safe by slowing the car without fail, hundreds of times during a journey. Yet, it is also one of the most neglected fluids by a majority of car owners simply because it does its job so quietly and reliably and thus is easy to ignore.
Even the more diligent amongst us will check the brake fluid level in the reservoir, and top up when needed. But the real need is to keep the rest of the fluid in the brake up to par. Some people will argue that since the brake system is sealed, there is no need to change brake fluid at all.
However, remember that brake fluid is designed to be non-compressible so it transmit the pressure from the brake pedal to the brakes to slow or stop the vehicle. In order to do this over a long period of time, it needs to be hygroscopic i.e. to attract water moisture and keep it dissolved.
So how does the moisture get into brake fluid? The cap of the master cylinder reservoir is not tight enough, and neither are all the joints and rubber hoses in the system. With application of the brakes, all joints undergo expansion and contraction due to heating and cooling, which allow minute quantities of leakage. Over time, this moisture content builds up in the brake fluid.
Brake fluid is designed to keep this water content dispersed evenly within itself. As the amounts of water increases over the years, two important things happen: the compressibility of the brake fluid increases and its boiling point drops. What this means in practical terms is that the brake pedal gets spongier with time and the brakes lose their efficiency under stressful conditions, for example driving down a mountain highway. Given enough neglect, this situation can get even worse. If the water content increases to more than a few percent of the fluid, it will form droplets that will sink down to the lowest points on the brake lines, since water is heavier than brake fluid. When brakes are applied suddenly enough to cause overheating, this pooled water will flash suddenly into steam, which of course is highly compressible. The end result is a sudden and catastrophic loss of braking. (This is the real reason a car used for years in Lahore suddenly has an accident on the way way back from Murree on the long awaited family trip due to sudden brake failure, leading to an entirely avoidable tragedy.)
With this background, let us do the right thing, Pakwheels style, and change the brake fluid in our cars once every two or three years at the most.
This is a very easy procedure. You will need a new sealed container of the correct type of brake fluid, a small length of rubber tubing, a small glass container, and the appropriately sized ring or flare wrench. Most cars will take DOT3 or DOT4 fluid, and the wrenches are usually 6 or 8 mm in size. A friend to help and a safe working space where access to the bleeder screws is easy are essential.
First of all, clean the reservoir cap and fill up the fluid to the maximum line if it is low. Keep an eye on this level throughout this procedure and never allow it to drop below the low level marked. This means periodically checking the level and adding more fluid, say once every few pumps of the brake pedal, as you will read later in this piece. Next, figure out the order in which the wheels will be bled, starting from the one furthest away from the reservoir and working closer. Thus for a right hand drive vehicle, where the reservoir will probably on the right (driver’s) side of the engine bay then the order will be left rear, right rear, left front and then right front wheel. If the reservoir is on the left side, then the order will be right rear, left rear, right front and then left front.
Now the basic procedure to be repeated at each corner is this. Clean the bleeder screw and loosen it with the proper wrench. With the wrench in place, attach the rubber tube over the bleeder nipple and dip the other end in the glass container with a little bit of brake fluid in it so that there is no chance of sucking back air. Ask the friend to sit in the vehicle with the windows open so that you can communicate. The friend presses the brake pedal till it is firm. Loosen the bleeder screw so that the fluid under pressure comes out the attached tube. The brake pedal will sink to the floor as the fluid bleeds out. You tighten the bleeder crew and then your friend slowly releases the brake pedal, and then presses it again a few times till the pedal is firm again. Then you loosen the bleeder screw for more fluid to drain and then tighten it. Then your friend releases the pedal and pumps it again. And so on.
This process is repeated at each corner in the correct order until the new brake fluid, which is usually much lighter in color compared to old fluid is seen to come out into the container with absolutely no air bubbles in it. It can take up to 10-15 times for the first corner and 4-8 times for the closest corner, so work slowly and methodically with attention.
Please do not forget to periodically top up the reservoir every few times a bleeder screw is opened. If it is emptied, air will be sucked into the master cylinder and may be even the high pressure ABS pump if the car is so equipped, and it will be major (and expensive) headache to properly bleed both.
At the end, top up the reservoir again, and make a slow test drive to check operation of the brakes. If done properly as described, you will be surprised at the improvement in the braking feel, just like when the car was new. For the next few days, keep an eye on the brake level to make sure that it does not drop. If it does decrease, check all the bleeder screws for being properly tightened.
And that is how you keep the brake fluid new, Pakwheels style!