Which brakes to bleed first

Most brake fluid types are hygroscopic. They absorb moisture from the atmosphere. When brake fluid has a high moisture content, the heat from the brakes is absorbed by the brake fluid. Also, the moisture, if ignored, will cause rust to form inside the calipers and master cylinder. Brake fluid types are coded, and the type to be used will be marked clearly on your fluid reservoir cap.

It will be marked Dot 3, 4, 5, or 5. I like to keep things simple. You can divide brake fluid into 2 types — Glycol or Silicone based.

Glycol-based compatible families of fluids are Dot 3, Dot 4, and Dot 5. Basically, the amount of heat they withstand before boiling, higher is better.

But use whichever fluid is marked on your cap. Also important to note Glycol-based fluids will strip paint, so careful splashing this stuff around. Silicone-based Dot 5 fluid must not be mixed with Glycol-based Dot 3, 4, or 5. If mixed, these fluids will turn into sludge in the system, and the pedal will feel like a pillow.

During brake bleeding, the master-cylinder cap should be left unscrewed but still in place atop the reservoir. Each brake must be bled in the correct sequence. Generally, you bleed the brake most distant from the master cylinder first, but some cars require a different order. Make sure the tubing is long enough so that you can hang the catch container above the height of the bleeder screw; this will keep any air trapped in the tubing from sneaking back into the caliper.

STEP 6: It's time to get your able assistant involved. Have them maintain pressure on the pedal. STEP 7: While the assistant maintains pressure on the pedal, open the bleeder screw a small amount.

Fluid will pass through the clear tube, and the pedal will begin dropping toward the floor. Have them continue pressing the pedal towards the floor. STEP 9: Repeat steps six through eight at least five times at that wheel location until the stream of fluid flowing through the clear tubing is free of air bubbles. STEP Now repeat steps six through 9 at the remaining three brake locations in the proper sequence.

That means moving from the wheel farthest away from the master cylinder to the one next closest and so on. STEP When you've completed bleeding all four brakes, ask your assistant to apply full effort to the brake pedal followed by an abrupt release of that effort. Observe the motion of the fluid in the master-cylinder reservoir.

Sometimes, it can be the result of a service procedure or an upgrade — such as replacing the stock flex lines with stainless steel braided lines. But often it is the result of high temperatures that cause brake fluid components to boil, thus releasing gasses from the boiling fluid into the brake hydraulic system.

This leads one to contemplate the type of liquid that is used as brake fluid. In theory, even simple water would work — since, being a liquid, water cannot be compressed. However, it is important to remember that the fundamental function of the braking system is to convert kinetic energy into heat energy through friction.

And the reality of this process is that certain parts of the braking system will be exposed to very high temperatures. In fact, it is not uncommon to see rotor temperatures during a race as high as degrees Fahrenheit — which can raise the temperature of the brake fluid to well over degrees Fahrenheit. Since the boiling point of water is degrees Fahrenheit, it is easy to see that water within the brake system could boil easily — and therefore release gases into the brake pipes — which would reduce the efficiency of the system.

Water would also present a big problem in cold weather if it froze to ice! The "obvious" solution to this problem is to utilize a fluid that is less sensitive to temperature extremes. Hence the development of "brake fluid. And like most things in the world, the addition of certain beneficial characteristics usually brings tradeoffs in other areas. In the case of brake fluid, we generally must balance the fluid's sensitivity to temperature against its cost and its impact upon other components within the system.

Stated more bluntly, it is possible to reduce a fluid's sensitivity to temperature by varying the ingredients of the fluid. However, certain combinations of ingredients can significantly increase the cost of the fluid and may react with OEM materials to damage seals and induce corrosion throughout the braking system.

Add a comment. Active Oldest Votes. Improve this answer. This works well for most systems. There are published procedures for every vehicle and most follow this general rule, some do not.

I modify this by first bleeding any lines that are known to have air and then go around again following the published pattern. This method results in the least rework. Great explanation! Though can this be applied to diagonally split and ABS systems? The posted diagram does not represent modern braking systems. This seems like "old timey" wisdom that we've somehow held on to. Perhaps I should bleed both of them again as I only did them once. I was cold and in a rush to get them done.

They appear to be fine. Have a look at my answer here : mechanics. Sign up or log in Sign up using Google.