How to bleed your Shimano brake
On a bike, every component has a purpose. The functionality of the brakes is probably the most important. It is essential for survival, a failure at the wrong moment can end disastrously. For this reason, it is advantageous to know about the functioning of the installed brake unit. A regular check-up of the brake pads or brake linings should become routine. Highly frequented use naturally causes signs of wear. Particularly with hydraulic brake systems, braking performance can also decrease if air gets into the brake lines. The remedy is bleeding. Here you can find out everything you need to know about bleeding hydraulic disc brakes.
- What types of brakes are there on a bicycle?
- Why do you bleed a brake?
- How often should you bleed Shimano brakes?
- How to bleed the brakes yourself?
1. What are the types of brakes on a bicycle?
Bicycles usually have rim brakes or disc brakes. Often, for example, road bikes, gravel bikes, mountainbikes, trekking bikes or city bikes are equipped with rim brakes. When the brake lever on the handlebar is actuated, brake pads are pressed against the rim on both sides of the wheel. The resulting friction throttles the speed. Rim brakes are lighter and usually cheaper compared to disc brakes. They are also very robust. However, the rims wear out due to the resulting friction and heat. In wet conditions, the braking performance is reduced. Disc brakes are common on modern bikes of all types. Brake discs are attached to the hubs of the wheels. When the brake lever is pulled, two brake pads press on the discs from both sides and slow the bike down. Both rim brakes and disc brakes are installed in different modes of operation. The braking force can be transmitted hydraulically or mechanically. Hydraulic brakes need to be bled from time to time. They contain a closed fluid system. Hydraulic disc brakes are often installed, especially on mountain bikes. Mineral oil runs through the brake cables. This cannot be compressed. When the rider pulls the brake lever, pressure is applied to the caliper. This causes the brake pads to press against the brake disc.
2. Why do you bleed a brake?
If the decrease in braking power is noticed, the components should first be checked for wear. After that, there are other possible causes. If the brake elements are dirty or overheated, losses also occur. Cleaning them or letting them cool down will quickly remedy these deficiencies. When cleaning brake discs and brake pads, no oil or grease should get on the elements. If you take your bike out on long tours in the mountains, you regularly risk overheated brakes. Before buying, you can look for brake pads that have been thermally pre-treated and are thus somewhat more temperature-resistant. If the brake has been in use for some time, the pressure point may shift backwards. An indication of this is that the brake lever has to be pulled further than usual to trigger braking. However, this can also be an indication of worn brake pads.
If there is indeed a shift in the pressure point, it is obvious that air has entered the brake system. The brake fluid in the lines can therefore no longer transmit the pressure ideally after the brake levers have been actuated. You can seal brake systems as well as you like, but air will still find its way inside after a while. That's not so bad. Even inexperienced hobbyists can bleed Shimano disc brakes on their own and save money at the bicycle workshop. It doesn't take much time. Especially with a bleeding kit, also called a bleed kit, the brakes are properly adjusted again in no time. By the way, it can be used several times, this investment is worthwhile. Whether Shimano XT, Deore, XTR, SLX or other models of disc brakes, bleeding works identically.
3. How often should you bleed Shimano brakes?
How often the brakes should be bled is not clearly regulated. As soon as the pressure point becomes spongy and moves backwards, bleeding is usually necessary. It is not possible to predict exactly how often this will be the case. Normally, bleeding should not be necessary more often than once a year, or even less often. Otherwise, various seals are probably outdated and should be replaced by a specialist workshop.
4. How do you bleed the brake yourself?
Although the brake is the most important thing to ensure your own safety, you can bleed your own brake on your own without any previous experience. There are two options to bleed the brakes on your own. The first option of bleeding, which is presented here, is not as thorough as the second. On the other hand, it is particularly fast. In addition, a complete bleeding kit is not required, only a bleeding funnel. It is best to clamp the bicycle in an assembly stand or to clamp it in such a way that a secure hold is guaranteed. Align the brake lever of the brake to be bled horizontally. The corresponding wheel must be dismantled. The opening with the bleeder screw should become the highest point of the system. The screw can now be unscrewed. The funnel is inserted into this opening. Then some Shimano mineral oil can be put into the funnel. The brake lever is now repeatedly tightened a little and left loose. Meanwhile, the bike should be tilted slightly. Air bubbles will rise and become visible in the fluid in the funnel. If no more air reaches the surface, you are done.
Preparation for complete ventilation
To bleed the brake system completely, a number of tools are needed in addition to the bleeding kit. Screwdriver, needle-nose pliers, Allen key, open-ended spanner and torque spanner, as well as a few rags come into use. When buying the service kit, by the way, make sure that it is designed for the particular brake system that is to be bled. In most cases it contains mineral oil, which must be from the same manufacturer as the brake system. Bleeding kits from Magura or Sram are therefore unusable for a Shimano brake. The piston seals can be damaged by foreign hydraulic oil. The Shimano bleeding kit should contain the bleeding funnel as well as syringe, hose and oil stopper. Many kits also include the mineral oil, but not all. Clean work is essential for the bleeding itself. After all, no dirt should get into the brake system. It is best to clean the brake lever and caliper beforehand. A clean place for the tools is also important. During filling, it often happens that the mineral oil overflows or drips. For this, a few clean rags should always be at hand. If mineral oil runs onto the frame of the bike, the area can be cleaned with spirit. Other chemicals such as brake cleaner will attack the paint. Gloves can be worn to protect your skin from liquids and the resulting irritation. On particularly old models, there are equalisation reservoirs mounted on the brake lever. In this case, the cover must be removed for bleeding.
Complete ventilation in a quick run
- Remove the wheel
- Set the brake lever horizontally
- Remove brake pads
- Push brake piston completely backwards
- Push bleed block into brake calliper
- Prepare syringe and fill with mineral oil
- Attach syringe to brake calliper
- Remove bleed screw on brake lever
- Screw on funnel and fill
- Slightly unscrew bleed nipple on brake calliper
- Let mineral oil move from syringe to funnel
- Screw in and close bleed screw and bleed nipple
- Remove bleed block and fit brake pads
- Mount wheel and move brake lever back into position
- Test ride
Complete ventilation in detail
Here, the bike should be fixed with the help of an assembly stand or similar. A second person who can help in case of doubt does not hurt. Remove the wheel of the brake to be bled. As with the quicker version of bleeding, the brake lever of the brake to be bled is now placed horizontally. The bleeding screw should be the highest point in the system. The brake pads should be removed. Under no circumstances should oil get onto the brake discs or brake pads. To remove the brake pads, first remove the safety screw. The pads are removed. The pistons are carefully pushed back, for this you can use the so-called bleed block or something else blunt. This is also included in the bleed kit. The bleed block is now placed with the rounded side first in the place of the pads, in the brake calliper. The bleed block can be fixed with the safety screw. This holds the pistons in position. The syringe can be prepared by turning the adapter onto it and then putting the hose with clamp onto the adapter. You will find all parts in the bleeding kit. The syringe can then be filled with mineral oil. About a quarter of the syringe should be filled with the fluid. It is especially important not to let any air get into the syringe. To do this, close the clamp on the adapter after filling. Now place the syringe on the bleed nipple with a little pressure on the brake calliper. The bleed nipple is usually protected by a rubber cover, which must be removed beforehand. There is an expansion tank on the brake lever. The bleed screw located here is removed. It is fitted with a sealing ring that must not be lost. The funnel can be screwed into the opening of the bleeder screw. About one centimetre of the funnel is filled with mineral oil. The bleed nipple on the brake calliper should be opened by a quarter turn. A 7 mm open-end spanner or a hexagon socket is needed for this. Use the syringe to feed the mineral oil into the brake system. The fluid rises in the funnel on the brake lever and air bubbles rise. The contents of the syringe should not be completely emptied. It is important not to introduce new air into the system through this step.
A look into the funnel reveals whether the mineral oil is still good. If it is a different colour than the new fluid or if there are foreign bodies in it, it must be collected in the funnel and disposed of. To completely bleed the brake system, the syringe can be drawn up with oil and then emptied again. The mineral oil is thus moved back and forth between the funnel and the syringe. It is important never to empty the syringe completely so as not to introduce air into the system. During this process, you can always pull the brake lever and carefully tap the brake lines. In this way, air bubbles rise in the funnel. The last air pockets disappear. Difficulties can arise especially when bleeding the rear brake. This is caused by improperly routed brake lines. If they are routed in a particularly curvy manner, this makes the bleeding process more difficult. To remedy this, lay the brake lines as straight as possible. By unscrewing the brake caliper and letting it hang, the entry point of the mineral oil can be shifted particularly far downwards. Hopefully, this will make it easier for the air to rise through the funnel to the outside. As soon as no more air bubbles rise in the funnel, the bleed screw on the brake calliper can be closed. The bleed screw must be closed with a torque of 4-6Nm. A small torque spanner is needed for this. After the syringe has been removed, the rubber cover can be put back on the bleed nipple. The brake caliper is cleaned with a clean rag. After pulling the brake lever a few times, the pressure point is normally ideally seated again. The funnel is closed with the funnel plug and then unscrewed. The mineral oil should be up to the screw-in opening. The bleed screw and seal are screwed back into the brake lever. It should not be screwed in too tightly. Old mineral oil from the funnel and syringe are disposed of properly. Any areas on the bike that have come into contact with mineral oil should be cleaned with methylated spirits. When the pressure point has moved further forward again, the bleed block can be removed and the brake pads inserted. Once the wheel is remounted and the brake lever is correctly aligned, the MTB or road bike is ready to ride again. After a successful bleeding, the bike can be test ridden. When doing so, you should make sure that the brake engages much earlier in the best case. The pressure point moves forward again. If you are still used to the old brake, you may brake too hard. If there is no or hardly any change in the pressure point after bleeding, this may be due to the seals. Age and wear cause problems. The seals should be replaced in a specialist workshop to make them impermeable to air again.
If you feel uncomfortable with the bleeding process, you can of course go to a bicycle workshop. After all, there are a few points you have to pay attention to for a clean result. Only by bleeding several times do you develop a routine and realize what is really important. Nevertheless, bleeding can also be done at home and without prior knowledge. The best thing to do is just to try it out. If you have any questions about the brake system, the buycycle team will be happy to help you.
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