Brake bleeding: Difference between revisions
No edit summary |
m Reverted edits by 2402:800:61B1:C076:7134:F6F2:433F:30B6 (talk) to last version by Sammi Brie |
||
| (32 intermediate revisions by 21 users not shown) | |||
| Line 1: | Line 1: | ||
{{Short description|Procedure performed on hydraulic brake systems}} |
|||
| ⚫ | |||
{{refimprove|date=June 2018}} |
|||
| ⚫ | |||
'''Brake bleeding''' is the procedure performed on [[hydraulic |
'''Brake bleeding''' is the procedure performed on [[hydraulic brake]] systems whereby the brake lines (the pipes and hoses containing the [[brake fluid]]) are purged of any air bubbles. This is necessary because, while the brake fluid is an [[compression (physics)|incompressible]] [[liquid]], air bubbles are [[compression (physics)|compressible]] [[gas]] and their presence in the brake system greatly reduces the hydraulic pressure that can be developed within the system. The same methods used for bleeding are also used for '''brake flushing''' or purging, where the old fluid is replaced with new fluid, which is necessary maintenance. |
||
The brake fluid capacity of a typical automobile is around 500ml. [[Brake fluid]] is [[toxic]], and must be handled carefully and disposed of properly. Most cars use DOT 3 or 4 Brake fluids, which may be mixed, but DOT 5 is silicone based and not compatible with DOT 3 or 4. Most types of brake fluid harm automotive paint and plastics on contact, so special care must be taken when using this fluid: any spills must be immediately cleaned up. Brake fluid is water soluble so it may be rinsed off with water. |
|||
==Methods== |
|||
The process is performed by forcing clean, bubble-free brake fluid through the entire system, usually from the [[master cylinder]](s) to the calipers of [[disc brake]]s (or the [[wheel cylinder]]s of [[drum brake]]s), but in certain cases in the opposite direction. A brake [[bleed screw]] is normally mounted at the highest point on each cylinder or caliper. |
The process is performed by forcing clean, bubble-free brake fluid through the entire system, usually from the [[master cylinder]](s) to the calipers of [[disc brake]]s (or the [[wheel cylinder]]s of [[drum brake]]s), but in certain cases in the opposite direction. A brake [[bleed screw]] is normally mounted at the highest point on each cylinder or caliper. |
||
There are five main methods of bleeding:<ref>[http://www.brakebleeder.com/solutions/bleeding-brakes/bleeding-methods/ Brake Bleeding Methods] by Phoenix Systems</ref> |
|||
''The following description of brake bleeding techniques is intended only to provide an overview of the common methods, and is not to be used as specific instruction. The actual procedure varies from one vehicle to another and the manufacturers' shop manual procedure should be used.'' |
|||
*The ''pump and hold method'', the brake pedal is pressed while one bleed screw at a time is opened, allowing air to escape. The bleed screw must be closed before releasing the pedal, or a [[one-way valve]] must be fitted. |
|||
*In the ''vacuum method'', a [[vacuum pump]] is attached to the bleeder valve, which is opened and fluid extracted with the pump until it runs clear of bubbles. |
|||
*In the ''pressure method'', a pressure [[pump]] is attached to the master cylinder, pressurizing the system, and the bleeder valves are opened one at a time until the fluid is clear of air. Specialised pumps may incorporate a method to automatically keep the brake fluid reservoir full during bleeding. |
|||
| ⚫ | |||
*''Gravity bleeding'' is a simple and easy method replace automotive brake fluid. It can also be used to bleed systems containing air bubbles but may not be as effective as other methods. |
|||
==Pros and cons of different methods== |
|||
There are four main methods of bleeding: Pump & Hold (2 variations), Vacuum, Pressure, and Reversed Pressure. Pump & Hold generally requires two people, the other methods can be done by a single person. |
|||
The pump and hold method usually requires two people, although it can be performed by one person if one-way bleed nipples or valves are fitted. During this method, the brake pedal and master cylinder piston will travel beyond their normal range which can cause wear on seals or incorporate corroded metal into the brake fluid. |
|||
Multiple wheel cylinders or calipers can be bled simultaneously, although this is only usually done with the gravity method which doesn't require pumps. The gravity method does take a long time, typically several hours to replace all the fluid. Bubbles in the system may rise faster than the fluid drains, so it may not be effective at bleeding, but is generally sufficient for replacing old fluid with new. Gravity bleeding is a very simple method requiring only one person. When the reservoir cap is removed and a bleed nipple opened, fluid drips slowly from the nipple because it is lower than the reservoir. A hose is typically used to collect the fluid in a container for safe disposal. The reservoir must be kept above the min mark at all times to avoid more air being drawn into the system. |
|||
*Pump and Hold Method, two people: One person pumps the brake pedal to compress the air, then holds pressure on it. The other person opens the bleeder valve to let out fluid and air, then closes the valve after the pedal has landed (to prevent air being sucked back in through the valve on the upstroke). The process is repeated, usually many times, for each wheel. Typically a length of clear tubing is connected to the bleeder valve and run to a container during the process, both to collect the toxic brake fluid and to better view the fluid and bubbles. The master cylinder reservoir must be replenished frequently, for if it goes dry the entire process must be redone. The cover must be left loose so that the fluid may be drawn, but should be in place so that fluid does not squirt out on the return stroke. A block may be placed under the pedal so that it does not bottom out during this procedure, as the master cylinder seals could be damaged by encountering accumulated sediment and / or corrosion. |
|||
Applying [[pressure]] to the reservoir or bleed nipples, or applying a [[vacuum]] to the bleed nipples, makes the fluid flow through much more quickly than gravity alone. Replacing all the fluid takes only a few minutes. |
|||
*Pump and Hold Method, One Person Option: This uses either a "one man" bleeder tool, consisting of a one way valve (check valve) at the end of a length of tubing which is attached to the bleeder valve, or a special one way bleeder valve. These methods have the disadvantage that air is sometimes sucked back into the system via the bleeder valve threads, this can be alleviated to a degree by using [[Teflon tape]] on those threads. This method is not recommended because with only one person there is no way to verify if indeed the fluid that is coming out of the bleeder valve has any air present, such as from a bad master cylinder or improper/incomplete bleeding. |
|||
Different vehicles have different recommended bleeding patterns. Brakes are usually bled starting with the wheel that is furthest from the master cylinder and working towards the wheel closest to the master cylinder. This prevents bubbles in the system being forced into pipes towards wheels that have already been bled. |
|||
*Vacuum Method: The master cylinder is topped off and the cover left loose. A specialized vacuum pump is attached to the bleeder valve, which is opened and fluid extracted with the pump until it runs clear of bubbles. Once again, the master cylinder reservoir level must be maintained. The vacuum method can also draw in air via the bleeder threads, so the bubbles will never clear. However, this does not mean there is still air in the brake lines. Using Teflon tape on the bleeder threads will alleviate this issue and allow you to accurately determine when you have evacuated all air from the system. |
|||
==Bench bleeding== |
|||
*Pressure Method: A specialized pressure pump, is attached to the master cylinder and filled with fluid. The pump is used to pressurize the system to about 10psi, and the bleeder valves are opened one at a time until the fluid is clear of air. One advantage to this system is that the pump reservoir usually holds enough fluid that running dry is not likely. This is the method most professional shops use. |
|||
| ⚫ | After replacement of the master cylinder, the master cylinder is usually "bench bled" before installation. Typically by securing it on the bench, filling it with fluid, connecting fittings and hoses to route fluid from the outlet ports on the master cylinder back to its reservoir, and repeatedly depressing the master cylinder plunger until bubbles are no longer seen coming from the hoses. |
||
==Clutch bleeding== |
|||
| ⚫ | |||
The same techniques are used for bleeding hydraulic [[clutch]] systems. A bleed nipple on the clutch [[slave cylinder]] is used. Gravity bleeding is often not effective because of the layout of the clutch pipework. |
|||
==References== |
|||
The order in which the wheels are bled is specified in the specific vehicle's shop manual. Typically the wheel farthest from the master cylinder is done first, working toward the closest wheel last. |
|||
{{reflist}} |
|||
| ⚫ | |||
== External links == |
== External links == |
||
{{Wikibooks |Automotive Systems|Braking System}} |
|||
* [http://www.lexls.com/tutorials/brake/bleeding.html Another "how to" on bleeding brakes.] |
* [http://www.lexls.com/tutorials/brake/bleeding.html Another "how to" on bleeding brakes.] |
||
* [http://www. |
* [http://www.brakebleeder.com/videos/reverse-brake-bleeder-videos/ How To Bleed Your Brakes By Yourself In Less Than 10 Minutes] |
||
* [http://www.how-to-bleed-brakes.com How to bleed brakes in 10 Minutes with only 1 Man. Brake Bleeder Video.] ('''MARKETING AD - DEAD VIDEO LINK''') |
|||
{{Powertrain}} |
{{Powertrain}} |
||
Latest revision as of 10:03, 9 February 2023
 | This article needs additional citations for verification. (June 2018) |
Brake bleeding is the procedure performed on hydraulic brake systems whereby the brake lines (the pipes and hoses containing the brake fluid) are purged of any air bubbles. This is necessary because, while the brake fluid is an incompressible liquid, air bubbles are compressible gas and their presence in the brake system greatly reduces the hydraulic pressure that can be developed within the system. The same methods used for bleeding are also used for brake flushing or purging, where the old fluid is replaced with new fluid, which is necessary maintenance.
Methods
[edit]The process is performed by forcing clean, bubble-free brake fluid through the entire system, usually from the master cylinder(s) to the calipers of disc brakes (or the wheel cylinders of drum brakes), but in certain cases in the opposite direction. A brake bleed screw is normally mounted at the highest point on each cylinder or caliper.
There are five main methods of bleeding:[1]
- The pump and hold method, the brake pedal is pressed while one bleed screw at a time is opened, allowing air to escape. The bleed screw must be closed before releasing the pedal, or a one-way valve must be fitted.
- In the vacuum method, a vacuum pump is attached to the bleeder valve, which is opened and fluid extracted with the pump until it runs clear of bubbles.
- In the pressure method, a pressure pump is attached to the master cylinder, pressurizing the system, and the bleeder valves are opened one at a time until the fluid is clear of air. Specialised pumps may incorporate a method to automatically keep the brake fluid reservoir full during bleeding.
- In the reverse method, a pump is used to force fluid through the bleeder valve to the master cylinder. This method uses the concept that air rises in liquid and naturally wants to escape up and out of the brake system.
- Gravity bleeding is a simple and easy method replace automotive brake fluid. It can also be used to bleed systems containing air bubbles but may not be as effective as other methods.
Pros and cons of different methods
[edit]The pump and hold method usually requires two people, although it can be performed by one person if one-way bleed nipples or valves are fitted. During this method, the brake pedal and master cylinder piston will travel beyond their normal range which can cause wear on seals or incorporate corroded metal into the brake fluid.
Multiple wheel cylinders or calipers can be bled simultaneously, although this is only usually done with the gravity method which doesn't require pumps. The gravity method does take a long time, typically several hours to replace all the fluid. Bubbles in the system may rise faster than the fluid drains, so it may not be effective at bleeding, but is generally sufficient for replacing old fluid with new. Gravity bleeding is a very simple method requiring only one person. When the reservoir cap is removed and a bleed nipple opened, fluid drips slowly from the nipple because it is lower than the reservoir. A hose is typically used to collect the fluid in a container for safe disposal. The reservoir must be kept above the min mark at all times to avoid more air being drawn into the system.
Applying pressure to the reservoir or bleed nipples, or applying a vacuum to the bleed nipples, makes the fluid flow through much more quickly than gravity alone. Replacing all the fluid takes only a few minutes.
Different vehicles have different recommended bleeding patterns. Brakes are usually bled starting with the wheel that is furthest from the master cylinder and working towards the wheel closest to the master cylinder. This prevents bubbles in the system being forced into pipes towards wheels that have already been bled.
Bench bleeding
[edit]After replacement of the master cylinder, the master cylinder is usually "bench bled" before installation. Typically by securing it on the bench, filling it with fluid, connecting fittings and hoses to route fluid from the outlet ports on the master cylinder back to its reservoir, and repeatedly depressing the master cylinder plunger until bubbles are no longer seen coming from the hoses.
Clutch bleeding
[edit]The same techniques are used for bleeding hydraulic clutch systems. A bleed nipple on the clutch slave cylinder is used. Gravity bleeding is often not effective because of the layout of the clutch pipework.
References
[edit]- ^ Brake Bleeding Methods by Phoenix Systems
External links
[edit]
