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Tuesday, June 19, 2012

Brake Bleeding Practical Procedure By Only One Mechanic

Procedure with photographs and video described here is the work of my innovation and it is easy to apply and designed to be done by only 1 (one) mechanic. Tools needed are combination spanner, hose, and container for used brake fluid. At first glance this brake bleeding procedure is similar to the one that already exist. But by lifting the hose higher than nipple and using grease to prevent air enter the system, this procedure can be done by one person only. No need helper to open and close nipple many times. With this procedure brake air bleeding for one wheel can be done in just 15 minutes if no problems, to jack and remove the wheel can take longer. On some high ground clearance vehicles such as jeep, this procedure can be performed without removing the wheel. Likewise, if you have car lift, brake air bleeding can be done without removing wheels. As it is easy, a non experience person can do it. You can do it in your garage at home, in spare time on Sundays or holidays.

There is also a simple procedure using pressure pump to push fluid in reservoir and goes out from nipple. Also a procedure with vacuum pump to suck air and brake fluid from nipple. Although simple, both procedures need very expensive tool.

Video at the bottom of this post shows the clear brake fluid with air bubles and red colored brake fluid that come out from brake nipple and into the transparent hose. A new red brake fluid will replace the old clear brake fluid.

If you just done any repair on piston or cylinder on the wheel or the brake master cylinder (brake pedal cylinder), for example: seals replacement, it is necessary to bleed air from brake hydraulic system. Air trapped in the hydraulic system will cause brakes do not grip. When stepped, brake pedal stroke is long and straight to the floor, and feels like stepping on a balloon or rubber foam. This occurs because the physical properties of air that can be compressed or compressible and decrease the volume. While the brake fluid can not be compressed (incompressible), it’s volume always remain the same though under pressure.

Brake bleeding procedure is usually requiring two people. One person is in charge of pumping the brake pedal until the pressure builds up and pedal stroke is shorter, then hold the pedal in a depressed position. The other person will loosen brake nipple so the air can come out of the brake hydraulic system, and then immediately close nipple again. Brake pedal is then released and pumped again, and so on until the pressure is really up and normal, and pedal does not feel like stepping on a balloon anymore. This popular procedure is written on many website.

The video is showing brake bleeding when replacing an old brake fluid with new one. Usually brake fluid is changed every 2 years, please refer to your vehicle service manual. Replacement of brake fluid needs to be done because of moisture or water entering the hydraulic brake system, and also some other materials such as: dirt, rubber seal debris, rust, air.

This procedure can also be used to bleed air after major brake hydraulic repair, eg, replacement of rubbers in wheels piston or in the master cylinder piston. And can be applied to almost any vehicle using the hydraulic system, including motorcycles.

Bleeding should be started from the farthest wheel from the master cylinder. This is to ensure the air and the old brake fluid can get out quickly in large volume. For cars with the driver position on the right such as Indonesia, United Kingdom, Australia, Japan, Singapore, Malaysia, Hongkong, India, New Zealand, etc.. the farthest wheel is the rear left wheel. On some cars, the position of the brake master cylinder is not close to the drivers foot, eq. on the right for Indonesia. There are some European cars have master cylinder positioned on the passenger side. Maybe because those cars were originally designed with the driver's position on the left, but later modified to have the driver's position on the right to expand market share.

The first thing that needs to be done before bleeding the brake: open the brake fluid reservoir cap, check brake fluid level, top up to maximum is necessary. The photo below shows brake fluid reservoir pointed by red arrow. Smaller reservoir is for the clutch.

Clean outside the reservoir with water, the reservoir is watertight and can be sprayed with water. Open the reservoir cap, the cap on some vehicles have two parts. In the photo below shows the cap is opened and still another cap on the inside. 

Open the inside cap and attach to the outer cap. The inside cap prevents brake fluid to spill out but still allow air to enter or ventilation. Below photo shows the inside cap is attached to the outside cap. Note the clear Prestone brake fluid inside reservoir. Clear brake fluid will be replaced with a new red coloured brake fluid. Shown also in the photo the brake fluid is around the maximum level. 

Jack and remove the rear wheel farthest from the master cylinder, the left rear wheel for Indonesia. Make sure the jack is positioned securely. Position the removed wheel under the car and add a block of wood to help jack. As the photos below. 

Clean the brake and left rear wheel well with water to make it easier and cleaner to work. Shown in the photo below of a drum type of rear brake. On some vehicles have disc type rear brakes.

The air bleeding valve is designated by red arrow in the figure below. Located behind the brake drum, and it's rubber dust cap has already been removed. 

Loosen the nipple by combination spanner. The rear brake is usually using 8 mm sized combination spanner. Avoid using a open end spanner to loosen and tighten the nipple, because it only holds two corners of nipple bolt head and it can cause damage. In the photo below we can see how to loosen the nipple by ring part or combination spanner, it holds all corners of nipple bolt head and prevent the bolt head damage. 

No need to remove nipple, only loosen nipple to about 30 to 60 degrees of rotation. Usually there will be a drop of brake fluid if nipple is loosened to about 30 to 60 degrees of rotation. Tighten slightly to stop brake fluid drip as it will wait for the preparation and installation of hose and used fluid container.

Connect a transparent hose diameter 3/16 inch or 5 mm to nipple, as shown below. If the hose too small, it can be widened a little bit by heat in order to fit it to nipple. If the hose too big, then use a smaller rubber hose. As far as I know the smallest diameter of transparent hose is 3/16 inches. There are rubber hoses with smaller diameter, and rubber hose is far more flexible then plastic hose. But the rubber hose is not transparent so we cannot see and check if any air bubbles inside the hose. So if the nipple is too small, connect a rubber hose to nipple, and then connect that rubber hose to a transparent plastic hose. This way we can clearly see and check fluid inside the transparent plastic hose.

At a distance of about 50 cm of hose from the nipple, tie a yarn. This yarn glued to the vehicle body with duct tape (adhesive tape) to make a loop. The higher hose loop peak, the easier for air to come out of hydraulic system as air in brake fluid try to go up to higher place. The yarn does not block the view when we look at top of the hose where air bubbles are gathered. The other end of the hose is inserted into a container. Make sure the hose is not leaking. Leaking hose will allow air to enter the hydraulic system. A leaky hose can also spray brake fluid and damage car paint. Immediately flush with clean water if the paint sprayed with brake fluid.

In the picture above shows a hose is connected to nipple, hose goes up as it is hung by yarn and duct tape on the car body. The other end of the hose is inserted into a container of mineral water plastic bottle, make sure this hose end reach the bottom of container. As container is filled by used brake fluid, fluid will prevent air to get into transparent hose via container. This will ensure only air from hydraulic system gathered at top hose, this way it will be easier to check if there is still air in hydraulic system. Although air may enter hose via container, it can't reach nipple as air can't go down passing through brake fluid by itself. We can see air bubbles from hydraulic system will be gathered at top of the hose, nothing air from container, then air is pushed by pedal pressure down into container.

That rised hose will help to remove air bubbles from brake hydraulic system. Air, steam and other gases have physical properties that lighter specific gravity then liquids. Air, steam, and other gases in the hose will try to go up to higher place when enter the hose together with brake fluid. So the air, steam and gases will 'try by themself' to get out of the brake hydraulic system.

Technique with a curved hose is often called as a goose neck system. This system is also applied to pump sewage water for garden, and the goose neck is used to remove air from the pump and water pipe.

Actual length of the hose is not necessarily the same lenght as the photo above. Since I will use that hose for other purposes, then I do not cut the hose.

To prevent outside air to enter the brake hydraulic brake system through some small holes (pores) around nipple, then apply grease around nipple and at the end of the hose that is attached to the nipple. See the photo below, green grease is pointed by green arrow.

When the hose and the container is ready, then loosen back nipel about 30 to 60 degrees. See a red arrow in the photo above, nipple is loosen and small amount of brake fluid comes out and enter into the transparent hose. This brake fluid has clear color, and will be drained and replaced with red brake fluid. If there are air bubbles in the hydraulic system, the brake fluid in the transparent hose will appear foamy or bubbly. Air bubbles will also be looking to move up as it try to get an higher place in the hose.

Ensure enough fluid in brake reservoir, top up with new brake fluid. The photo below shows red Prestone brake fluid is added. The red brake fluid is over maximum level. But because it will be drained, then the brake fluid level will be lower by itself.

Get inside the car and sit on to the driver's seat. Make sure the parking brake is released, so that all brake wheel cylinders will react when you step on the brake pedal, and release the trapped air and dirt in the wheel cylinder. Press or pump the brake pedal 5 times, the pedal stroke is long as brake fluid and air go out of loosened nipple. No need to turn on the engine, as foot pressure is enough to pump the pedal. No need to open and close nipple many times.

If brake fluid is not going out yet, loosen nipple again to about 30 degrees more. Too loose nipple will cause too much brake fluid draining and emptying the reservoir, also causes the air easily enter from the gap around nipple thread.

After 5 times pumping the pedal, check brake fluid in reservoir tank, top up if it has reached a minimum level. Check nipple, hose and used brake fluid container on the wheel brake. Make sure there is no leak in the hose, especially on the connection between the hose to nipple. Fix hose connection and add grease if there are drops of brake fluid.

If everything is no problem, then move on and pump the brake pedal as much as 10-15 times. Do not do it in a hurry. Too many pumping will cause brake fluid reservoir empty and the master cylinder will suck air. Any air inside master cylinder will cause longer time to bleed the system.

For a sedan, usually 50-100 times pumping brake pedal is enough for each wheel to drain the old brake fluid and replace with new fluid. For air bleeding may need a little more pumping, especialy after major repair to master cylinder. Because air inside master cylinder must travel into all pipes and enter into wheel cylinders before it can get out of the brake hydraulic system.

The photo below shows the brake fluid after brake pedal pumped few times. Visible in the transparent hose, first clear brake fluid with air bubbles go out, pointed by red arrow. Brake fluid and air can not re-enter the nipple and come into the wheel cylinder as there is a valve mecanism in the master cylinder that makes the master cylinder works like piston pump.

Then the brake fluid is changed to red. Different color brake fluid is used to to distinguish the old brake fluid from new brake fluid. The hose with full red Prestone brake fluid is visible in the photo below, and no more air column inside the hose.

When brake fluid has been replaced with new one, shut nipple off with an open end spanner. Do not too tight as it can damage nipple bolt head. Red arrow in the photo above shows combination spanner which used its open end to close nipple. Open end spanner can turn nipple bolt head although the hose is still attached to the nipple.

Remove the hose and retighten nipple with ring part of combination spanner, do not too tight because it gets seized and difficult to loosen in the future. Brake fluid will seal any small holes (pores) to prevent seepage, after sometime nipple will be more tightened like glued. Photo below shows nipple is tightened with a ring spanner, which is the ring part of spanner is used to tighten the nipple.

Put the dust rubber cap on nipple, clean and wipe all parts and area moistened and dripped by brake fluid. Cleaned and dried area will help to spot any fluid leaks. Reinstall wheel, and lower the jack. Do not forget to tighten wheel nuts criss-cross to ensure wheel is really centrist.

The following video shows brake fluid inside the hose. At first clear colored brake fluid and many air bubbles are going out, followed by red colored brake fluid. At the end of the video we can see nipple is closed and the hose is removed. If you can't open the video in this page, please go to youtube: Brake air bleeding by one mechanic.

Proceed to the second furthest wheel from the master cylinder, it is the right rear wheel for the driver in the right position for cars in Indonesia. Then the left front wheel, and finally the right front wheel. Run test your vehicle and brake suddenly to ensure brake performance. Pedal will feel higher if air and old brake fluid are drained away, and step on pedal will not feel like stepping on foam or bubble.

Used brake fluid should not be recycled, because dirt and water can change the nature of brake fluid, although the visual look is still clean. Because brake fluid also functions to clean the hydraulic system, the brake fluid is made to have same chemical properties as soap. It can dissolve the dirt and water, so it can not be filtered. Old brake fluid can be used as component cleaner, particularly components made of plastic and rubber that are not oil resistant.

Do not dispose carelessly as brake fluid can contaminate the environment, if swallowed in large quantities can be harmful to health.


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