1
How to bleed your brakes
by Drift_Warrior
This tutorial is given purely for reference purposes. The use of any information within this article is done so at the vehicle owner's own risk. By hosting this article on the QSS website, the members and associates of QSS hold no responsibility for damges or injury incured by an inexperienced person doing a job such as what is outlined in this text. This kind of work is generally reserved for a professional mechanic. For a vehicle owner to do this kind of work they must be confident of their ability and skill in a mechanical sense.Ok, once again the disclaimer part is out of the way and we can get straight into the technical side of things.
There are a couple of different ways that you can bleed your brake lines. All have advantages and disadvantages but they all lead to basically the same outcome. We have to remove air from the brake system. Whether it's because you've done a brake upgrade or had you calipers rebuilt, there is no way possible that you'd have no air in your brake lines.
Having air in your brake lines is a problem that can undoubtably lead to a costly or even fatal accident. This is something no-one wants. So bleeding brakes after doing work on them is very important.
*Important Note* Brake fluid is a toxic chemical, and like all toxic chemicals they should not be induced. Avoid contact with skin and eyes. If contamination occurs flush thoroughly with fresh clean water and see medical advice. Keep away from children.
*Also note that brake fluid is corrossive. If it is spilled onto any painted surface it will strip or fade the paint. If fluid is spilled onto a painted surface, wash it off immediately with clean fresh running water.
*Brake fluid is hydroscopic (will absorb moisture from the atmosphere). Don't leave the lids off the brake fluid container or the brake resevoir any longer than is necessary as it will absorb moisture and will eventually lead to brake failure.
Method One - Gravity Bleed
OK, The first method used is the "Gravity Bleed" method. It's a simple procedure and for the first part only requires one person. A second person is however required for the second and final part of the bleeding process. What you'll need :-- Fresh unopened bottle of brake fluid
- Spanner to suit the hex on the bleeder nipple. Use a single hex spanner, not a multihex.
- A catch/drip tray to catch the bled-out brake fluid.
- Easy access to a garden hose to clean down after the bleeding.
2. It's unusual for a brake that was not worked on to have air in the line, especially as most brake master cylinders are seperated into front and rear and the only common denominator is the resevoir. But if you feel it necessary to bleed all the brakes after doing any work or if you are flushing the whole brake system then the following steps should be completed in order for each caliper.
3. Place the drip tray under caliper to be bled. Undo the bleeder nipple on the caliper. It only needs to be undone about a quater of a turn. If you need to undo it more than this or if you undo it until it comes out before any fluid comes out, then the bleeder should be replaced. They are available from all trade spare parts stores (eg. Repco, Auto-One, Checkpoint, Midas)
4. Keep the bleeder undone until brake fluid starts to come out of the nipple. It will have air bubbles in it and tend to spurt a little so be careful not to get it in your eyes or on your skin. Allow it to continue to run out slowly, checking every so often that the level in the resevoir doesn't drop below the LOW mark.
5. Once the fluid is coming out in a continuous stream, without any form of air bubbles, tighten the bleeder nipple up again.
*DO NOT tighten the nipple as if is were a structural bolt. Only tighten it until it seats firmly. They are a hollow bolt and can shear off if tightened too much*
Repeat steps 3 - 5 until all calipers in question have been bled.
6. Get someone to sit in the drivers seat. *Bare in mind the vehicle should still be on axle stands at this point in time. DO NOT let anyone including yourself get under the car. DO NOT rock or unbalance the car in any way or it can easily fall off the stands causing serious injury or death*
Once they are sitting in the drivers seat get them to depress the brake pedal and release it a few times (Normally 3 or 4 times will do) until they feel some resistance/pressure in the pedal.
7. Make them hold the pedal fully depressed and crack the bleeder nipple off slightly, a 1/16th to an 1/8th of a turn is normally enough. The brake fluid should ooze out gently bringing with it any little pockets of air that may still be in the caliper. *When doing this, the brake fluid is under pressure so it will spray out if you open the nipple too far* Get the person in the car to tell you clearly when the pedal hits the floor and has no pressure behind it. At this point, nip up the bleeder nipple again.
Repeat this step on each caliper in turn until a full strength pedal is reached. While doing this you are using a larger amount of fluid. Keep a careful eye on the fluid resevoir and fill it as soon as it reaches the LOW mark.
If this step is repeated more than 3 times on each caliper then proceed to step 6 - 8 in method 3 to allow an overnight bleed.
8. If a full pedal is reached, then you must fill the resevoir with brake fluid to the full mark and replace the cap. Re-fit the wheels to the vehicle and remove it from the axle stands. Move the vehicle into a clear open space and hose all the calipers, wheels and discs of the ones that were bled in order to flush off any run-off from the bleeding process. Brake fluid is hydroscopic, in other words it absorbs water and hence water is the best thing to wash brake fluid off with.
You can now take it for a drive and see how the brakes feel.
BE CAREFUL! If there is still some air in the system that you may have missed then as soon as the brakes are put under strain they can fail.Also keep in mind you have just hosed the wheels and brakes down, it may take a couple of presses on the brakes to remove any water from the discs so the calipers grab.
DO NOT drive fast, just a steady pace pressing on the pedal occasionally to ensure the pads are seating properly and the brake system is air free.
Method Two - Vaccuum Bleed
The second method is the "Vaccuum Bleeding" method. It does require special tools, but if you are able to get such tools it makes bleeding the brakes a simple one person procedure.Items needed :-
- Fresh unopened bottle of brake fluid
- Spanner to suit the hex on the bleeder nipple. Use a single hex spanner, not a multihex.
- A pressure bleeder. The one I use is a MityVac Vacuum/Pressure pump. They come fitted with a small bottle and hoses specifically for bleeding brakes.
- A catch/drip tray to catch the bled-out brake fluid.
- Easy access to a garden hose to clean down after the bleeding.
2. It's unusual for a brake that was not worked on to have air in the line, especially as most brake master cylinders are seperated into front and rear and the only common denominator is the resevoir. But if you feel it necessary to bleed all the brakes after doing any work or if you are flushing the whole brake system then the following steps should be completed in order for each caliper.
3. Place the drip tray under caliper to be bled. Place the spanner onto the bleeder nipple. Connect the hose from the bottle to the bleeder nipple.
Note the bottle has two hoses. The side of the bottle that has a hose leading into the bottle connects to the bleeder. The other side of the bottle connects to the vacuum side of the pump.
Pump the handle of the pump until it has a vacuum in the bottle (it should be showing vacuum on the guage). Undo the bleeder nipple on the caliper. It only needs to be undone about a quater of a turn. If you need to undo it more than this or if you undo it until it comes out before any fluid comes out, then the bleeder should be replaced. They are available from all trade spare parts stores (eg. Repco, Auto-One, Checkpoint, Midas)
4. Keep the bleeder undone until brake fluid starts to come out of the nipple. It will have air bubbles in it and this can be seen as it sucks into the bottle through the clear hose. Allow it to continue to suck out slowly until the guage reads nearly zero. DO NOT actually let the guage reach zero, nip up the bleeder nipple just before it does. Check every so often that the level in the resevoir doesn't drop below the LOW mark as this method will drain the resevoir quickly if you're not paying attention.
Continue to do this until no air is seen coming out of the bleeder nipple.
5. Repeat this process on each caliper to be bled. Once all calipers are bled, sit in the drivers seat. Depress and release the pedal a couple of times and a full pedal should be achieved.
*Bare in mind the vehicle should still be on axle stands at this point in time. DO NOT let anyone including yourself get under the car. DO NOT rock or unbalance the car in any way of it car easily fall off the stands causing serious injury or death*
6. If a full pedal is not reached then repeat steps 3 & 4 until it is.
7. If a full pedal is reached, then you must fill the resevoir with brake fluid to the full mark and replace the cap. Re-fit the wheels to the vehicle and remove it from the axle stands. Move the vehicle into a clear open space and hose all the calipers, wheels and discs and firewall in order to flush away any run-off from the bleeding process or spillage. Brake fluid is hydroscopic, in other words it absorbs water and hence water is the best thing to wash brake fluid off with.
You can now take it for a drive and see how the brakes feel.
BE CAREFUL! If there is still some air in the system that you may have missed then as soon as the brakes are put under strain they can fail. Also keep in mind you have just hosed the wheels and brakes down, it may take a couple of presses on the brakes to remove any water from the discs so the calipers grab.
DO NOT drive fast, just a steady pace pressing on the pedal occasionally to ensure the pads are seating properly and the brake system is air free.
Method Three - Standing Bleed(Overnight Bleed)
The third method is called the "Standing Bleed" or "Overnight Bleed". In itself, it is not the perfect way to bleed a brake system, purely because of the amount of time it takes. This is not really the way to bleed from the start but it does work and can actually assist in bleeding a system better if one of the previous methods hasn't worked to give you a full pedal. To use this to completely bleed a system, every step must be followed in order.
What you'll need :-
- Fresh unopened bottle of brake fluid
- Spanner to suit the hex on the bleeder nipple. Use a single hex spanner, not a multihex.
- A catch/drip tray to catch the bled-out brake fluid.
- Easy access to a garden hose to clean down after the bleeding.
- A piece of timber about 3 foot (900mm) long.
- A handful of thick padding rags.
1. Firstly, the car should still be on the axle stand from when the original brake work was done regardless of what it was. Having it on stands means you don't have to have the wheels on it and makes it easier to access the bleeder nipples.
2. It's unusual for a brake that was not worked on to have air in the line, especially as most brake master cylinders are seperated into front and rear and the only common denominator is the resevoir. But if you feel it necessary to bleed all the brakes after doing any work or if you are flushing the whole brake system then the following steps should be completed in order for each caliper.3. Place the drip tray under caliper to be bled. Undo the bleeder nipple on the caliper. It only needs to be undone about a quater of a turn. If you need to undo it more than this or if you undo it until it comes out before any fluid comes out, then the bleeder should be replaced. They are available from all trade spare parts stores (eg. Repco, Auto-One, Checkpoint, Midas)
4. Keep the bleeder undone until brake fluid starts to come out of the nipple. Allow it to continue to run out slowly, checking every so often that the level in the resevoir doesn't drop below the LOW mark.
5. Once the fluid is coming out in a continuous stream, without any form of air bubbles, tighten the bleeder nipple up again.
*DO NOT tighten the nipple as if is were a structural bolt. Only tighten it until it seats firmly. They are a hollow bolt and can shear off if tightened too much*
Repeat steps 3 - 5 until all calipers in question have been bled.
Yes, I know, so far this is no different to the "Gravity Bleeding" method outlined earlier, but at this point you'll see the difference.
6.Once all calipers are bled with the first part of the "Gravity Bleeding" method, sit in the drivers seat.
*Bare in mind the vehicle should still be on axle stands at this point in time. DO NOT let anyone including yourself get under the car. DO NOT rock or unbalance the car in any way of it car easily fall off the stands causing serious injury or death*
Pump the pedal until you feel it build up pressure under your foot. This may take up to a dozen pumps but it should happen.
7. Once the pedal has pressure against it, even though it may not be much it will still be enough to do what we need. Without removing your foot from the pedal, place the piece of timber on the pedal and wedge it between the pedal and the front of the seat. Remember to place the padding rags against the seat first to avoid damage to the trimming or fabric. Move the seat forward to hold the timber in place and still maintain pressure on the pedal.
The timber has to maintain the same pressure on the pedal as your foot was placing on it. This is the key to this whole theory. Once it's in place, exit the car and close the door.
At this point in time you can re-fit the wheels to the vehicle and remove it from the axle stands.
How can this work i hear you ask???
Well, when a fluid is under pressure so is any air that may be trapped in the fluid. Air, when under pressure and held in a liquid will rise easily. By doing this with the brake system and leaving it over night, the air trapped in the system will rise to the highest point, being the resevoir. In the morning you'll come out and find a heap of fluid missing from the resevoir.*
8. Leave the vehicle sit until morning and check the resevoir. There should be a fair amount of fluid missing from it. Remove the resevoir cap and fill to the FULL mark then replace the cap.
Remove the timber from the pedal and replace any fluid that may have been lost into the master cylinder by the pedal sucking back. Press on the pedal a couple of times and you should have a full pedal.
Move the vehicle into a clear open space and hose all the calipers, wheels, discs and firewall in order to flush away any run-off from the bleeding process. This can also be done before leaving the car sit overnight with the timber holding pressure on the pedal. As stated earlier, brake fluid will strip paint so any fluid spilled onto a painted surface should be washed off immediately. Brake fluid is hydroscopic, in other words it absorbs water and hence water is the best thing to wash brake fluid off with.
10. You can now take it for a drive and see how the brakes feel.
BE CAREFUL! If there is still some air in the system that you may have missed then as soon as the brakes are put under strain they can fail.Also keep in mind you have just hosed the wheels and brakes down, it may take a couple of presses on the brakes to remove any water from the discs so the calipers grab.
DO NOT drive fast, just a steady pace pressing on the pedal occasionally to ensure the pads are seating properly and the brake system is air free.
As stated earlier this is not by any means a conventional method of fully bleeding a brake system. In the even that one of the other two methods doesn't work you can easily use steps 6 - 8 to remove any air that may still be in the system and can't be bled by the first two methods. This doesn't often happen, but in the recent brake conversion I undertook I did have this problem. I used this exact method to correct it and I can definitely say that it does work.
I hope this tutorial can assist anyone looking at undertaking this task themselves. Always think safety first and don't take stupid risks.
