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    How to bleed a Shimano brake

    Sophia Willmes
    Sophia Willmes
    Mar 4, 2024 10 min
    How to bleed a Shimano brake

    Everything about the Shimano brakes bleeding

    On a bicycle, each component is provided with meaning. 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 linings should become routine. Highly frequented use naturally causes signs of wear. With hydraulic brake systems in particular, 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.

    1. What are the types of brakes on the bike?

    Bicycles usually have rim brakes or disc brakes. Often, for example racing bikes, 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 slows down 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 down the bike.

    Both rim brakes and disc brakes are installed in different modes of operation. The braking force can be transmitted hydraulically or mechanically. Hydraulic brakes must be bled from time to time. They contain a closed fluid system. Especially with mountain bikes, hydraulic disc brakes are often installed. Mineral oil runs through the brake cables. This cannot be compressed. When the rider pulls the brake lever, pressure is applied to the brake caliper. This causes the brake pads to press against the brake disc.

    Mountain bike red disc brake detail in the dark
    Photo by Jan Kopřiva / Unsplash

    2. Why do you bleed a brake?

    If the decrease in braking performance 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 pads, no oil or grease should get on the elements. Those who take their bike out on long tours in the mountains regularly risk overheated brakes. Before buying can pay attention to brake pads that are thermally pre-treated and thus somewhat more temperature resistant. If the brake has been in use for some time, it can happen that the pressure point moves backwards. An indication of this is that the brake lever must 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 are actuated. You can seal brake systems no matter how well, air will still find a way inside after some time. That's not so bad. Even inexperienced hobbyists can independently Shimano disc brakes and save money at the bicycle repair shop. It does not require a lot of time. Especially with a bleeding kit, also called 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 to the rear, bleeding is usually necessary. It is not possible to predict exactly how often this will be the case. Normally, bleeding should not be due more often than once a year, rather even less often. Otherwise, various seals are probably outdated and should be replaced by a specialist workshop.

    4. How to bleed the brake by yourself?

    Quick exhaust

    Although the brake is the most important thing to ensure your own safety, you can independently bleed your own brake without prior experience. There are two options to bleed the brakes independently. 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 needed, only a bleeding funnel. The bike is best clamped in a mounting stand or you clamp it that a secure hold is guaranteed. The brake lever of the brake to be bled is aligned horizontally. The corresponding wheel must be dismantled. The opening with the bleeding screw should become the highest point of the system. The screw can now be unscrewed. The funnel is inserted into this opening. Afterwards, some Shimano mineral oil can be added to the funnel. The brake lever is now repeatedly tightened a little and left loose. Meanwhile, you should tilt the bike slightly. Air bubbles rise and become visible in the fluid in the funnel. If no more air reaches the surface, you are finished.

    Preparation for Complete venting

    In order to completely bleed the brake system, quite a few tools are required in addition to the bleeding kit. Screwdriver, needle-nose pliers, Allen wrench, open-end wrench and torque wrench, as well as a few rags come into use. By the way, when buying the service kit, make sure that it is designed for the particular brake system that is to be bled. It contains in most cases mineral oil that 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 include the bleeding funnel and syringe, hose and oil stopper. In many kits, the mineral oil is also included, but not all. Clean work is essential in the bleeding itself. After all, no dirt should get into the brake system. It is best to clean the brake lever and caliper in advance. A clean storage area for the tools is also important. During filling, it often happens that the mineral oil overflows or drips. A few clean rags should always be handy for this. If mineral oil runs onto the frame of the bike, the area can be cleaned with mineral spirits. Other chemicals such as brake cleaner will attack the paint. To protect your skin from liquids and resulting irritation, gloves can be worn. On particularly old models, there are equalization reservoirs mounted on the brake lever. Here, the lid must be removed for bleeding.

    Penuel Bicycles in Inglewood, Ca.
IG: @whoistaylorsmith
    Photo by Taylor Smith / Unsplash

    Complete deaeration in a quick run

    1. Remove impeller
    2. Set brake lever horizontally
    3. Remove brake pads
    4. Push brake piston completely backwards
    5. Push bleed block into the brake caliper
    6. Prepare syringe and fill with mineral oil
    7. Apply syringe to brake caliper
    8. Remove bleed screw on brake lever
    9. Screw on funnel and fill
    10. Slightly unscrew bleed nipple on brake caliper
    11. Allow mineral oil to migrate from syringe to funnel
    12. Screw in and close the venting screw and venting nipple
    13. Remove bleed block and install brake pads
    14. Mount wheel and bring brake lever back into position
    15. Test drive

    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. The wheel of the brake to be bled is removed. As with the faster 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 dismantle, first remove the safety screw. The linings are removed. The pistons are carefully pressed back, for this you can use the so-called bleed block or something else blunt. This is also in the bleed kit. The bleed block is now placed with the rounded side first in the place of the pads, in the brake caliper. The bleed block can be fixed with the safety screw. This keeps 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. All parts can be found in the bleeding kit. The syringe can then be filled with mineral oil. Approximately one 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.

    The syringe is now placed on the bleed nipple on the brake caliper with a little pressure. The bleed nipple is usually protected by a rubber cover, which must be removed beforehand. There is an equalization reservoir 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 bleed screw. About one centimeter of the funnel is filled with mineral oil. The bleed nipple on the caliper should be opened a quarter turn. For this purpose, a 7 mm open-end wrench or a hexagon socket is required. With the help of the syringe, the mineral oil is fed into the brake system. The fluid rises in the funnel on the brake lever, and air bubbles also 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 color 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 the 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 accumulations disappear.

    Difficulties can arise especially when bleeding the rear brake. This is caused by improperly routed brake lines. If they are laid in a particularly curvy manner, this makes the bleeding process more difficult. To remedy the situation, 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 down. Hopefully, this will make it easier for the air to rise above the funnel to the outside. As soon as no more air bubbles rise in the funnel, the bleed screw on the brake caliper can be closed. The bleed screw must be closed with a torque of 4-6Nm. For this you need a small torque wrench. 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 the brake lever is pulled a few times, the pressure point normally sits ideally 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 together with the seal is 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. Places on the bike that have come into contact with mineral oil are 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 properly aligned, the MTB or road bike is ready to ride again. After successful bleeding, the bike can be test ridden. When doing so, you should make sure that the brake engages significantly 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 at a specialist workshop to make them impermeable to air again.

    If you are not sure about the bleeding process, you can of course go to a bicycle repair shop. After all, there are a few points that you have to pay attention to for a clean result. Only by bleeding several times you develop a routine here and realize what really matters. Nevertheless, bleeding is also feasible at home and without prior knowledge. It's best just to try it out. If you have any questions about the brake system, the buycycle-team with advice and to your side. Until then, we wish you: Happy fixing, happy braking, happy cycling!