How To: 12 Simple Steps to Bleeding Shimano Brakes

Words by: Max Morgan

In this next feature of our MTB How To, we will be going over how to bleed Shimano brakes properly. Bleeding your brakes is a regular maintenance service, necessary to ensure that your brakes are stopping like they should keep you safe out on the trails. Over time, brake pads wear down, mineral oil can deteriorate, and air can be introduced into the brake system. Here we will be going into detail on a complete bleed for any Shimano hydraulic disc brakes.

The brakes being serviced here are Shimano Saint 4 piston downhill hydraulic disk brakes. These brakes are strong and are Shimano's ultimate stopping power brake set for mountain bikes. The methods for bleeding both the front and rear brakes are the same.

Everyone has different tricks to bleeding their mountain bike brake system, and this is how we recommend bleeding all Shimano brakes specifically. To start, we are going to go over what tools are necessary to get the job done correctly. Without the proper tools, bleeding the brakes may not be safe and could cause them to malfunction on the trail. Bring your bike to a bike shop if you don't have the correct tools. 

What Tools Do We Need?

Most importantly, you will need Shimano Mineral Oil. Other brake manufacturers use either DOT brake fluid or other mineral oil. Mineral oil is a bit of a general term and it is very important to use Shimano specific mineral oil for all Shimano brakes. Using other types of fluid will breakdown the seals inside the brake system and could cause the system to fail. 

Secondly, you will need a Shimano Bleed Kit. Most Shimano bleed kits include the bleed cup, oil catch bottle, and syringe. Here we will not be using a syringe so you don't push any dirty fluid up through the brake lever. 

You will also need a Shimano bleed block to keep the brake caliper pistons spread apart throughout the bleeding process. Lastly, you will need a Phillips head screwdriver, a 7mm wrench, and a good set of Allen keys. 

1. Raise Brake Level To Parallel 

• First start by putting your bike in a stand and using a 4mm Allen key, raise the brake levers to where they are parallel to the ground. This will help keep mineral oil from spilling on to the brake lever and on to the ground. Tighten the brake lever bar clamp back down in that position. 

2. Remove Brake Pads

• Remove either the front or rear wheel depending on which brake you are going to be bleeding first. Remove the wheel and set it to the side for now. Next, remove the cotter pin and using a 3mm Allen key, remove the bolt that secures the brake pads to the caliper. 
  
  
• Be sure to set the brake pads out the way for now so they don't get contaminated with any mineral oil. If the brake pads get contaminated, they won't have the same stopping power as before. 

3. Install Bleed Block

• Use a tire lever to press out the caliper pistons if necessary. Do not use a metal screwdriver to do this or you might damage or possibly crack the ceramic pistons. Place the yellow Shimano bleed block into the brake caliper and secure it using the same bolt that holds the brake pads in. Tighten using a 3mm Allen key. 

4. Place Bleed Cup on Brake Lever

• Use a 2.5mm Allen key to remove the brake lever cap screw on top of the lever reservoir. Be sure not to lose the rubber O-ring at the base of the cap screw.
  
  
• Fill the bleed cup with Shimano Hydraulic Mineral Oil and screw it into the brake lever. Be careful not to cross thread the bleed cup into the lever. The threads are made of plastic and could be damaged easily without using caution. Make sure there is a rubber O-ring at the base of the bleed cup to ensure a complete seal. Without this, air may be introduced into the brake line. 

5. Attach The Oil Catch Bottle To Brake Caliper

• Press the rubber oil line on to the bleed port fitting near the top brake caliper bolt. Make sure to push the line all the way on to the fitting so that no air can get in and no oil can get out. Here the oil catch bottle is attached to the line but it is totally normal for the line to just be resting in the catch bottle. This is just for oil to drip into the catch bottle. 

6. Open Brake System at Both The Lever And Caliper

• Pull the plug sitting in the center of the bleed cup to allow the mineral oil to flow into the brake lever reservoir.
  
  
• Use the 7mm wrench to open the bleed port at the caliper an eighth of a turn. Now that both ends of the brake system are open, mineral oil will begin to flow and drip into the catch bottle. Allow the dirty mineral oil to fill the catch bottle until clean fresh mineral oil begins to come out of the caliper. You can see below that the nasty black oil has already been drained from the system and now clean oil is coming out.
  
  
• Make sure to continue to top off the mineral oil in the bleed cup. The key here is not to introduce air into the system through either open end of the brake system. If the steady dripping flow begins to slow down or stop you can push fluid through the line using the brake lever.  When you pull the brake lever and hold it closed, oil has been pushed through the line and out the caliper. Releasing the lever will create a vacuum at the caliper and you don't want that to happen. THIS PART IS VERY IMPORTANT.
  
  
• Pull the brake lever and hold it closed, tighten the bleed port at the caliper with a 7mm wrench, release the lever blade, and then open the bleed port again. Repeat this a few times to continue to push fluid through the caliper if necessary. 

7. Close Brake Caliper Bleed Port

• Use the 7mm open ended wrench to close the brake caliper bleed port. Remove the oil catch bottle and line from the brake caliper and keep in mind that some oil may spill on the caliper. 
  
  
• Make sure to dispose of the used dirty oil appropriately. 

9. Clean Brake Caliper and Install Brake Pads

• Make sure to keep the brake pads away from any of the mineral oil.  It is important not to make contact with the brake pad surface with your hands if possible. 
  
  
• Use any kind of degreaser or cleaner to thoroughly clean off the brake caliper before installing the brake pads. The Finish Line Citrus Bike Degreaser works perfectly for this.  Slide the brake pads into place remembering that Shimano's IceTech pads are particular to the left and right sides. Use a 3mm Allen key to secure the pads in place. Don't forget the small cotter pin!
  
  
• Place either the wheel back in the bike and tighten the axle appropriately. 

10. Cycle Brake Lever Blade 

• At this point, all your work at the brake caliper should be finished. Now we are going to wrap things up with a lever bleed in order to remove all the existing air bubbles that could be trapped in the brake line. With the bleed cup around half way filled, pump the brake lever repeatedly and watch for any air bubbles to come up to the top. Using a 4mm Allen key, loosen the brake handlebar clamp and position the breakup and down from parallel to retrieve any additional air bubbles. Be sure not to spill any mineral oil or allow air through the bleed cup. 
  
  
• Air bubbles like to get trapped in the intricacies of the brake lever. Use a Philips head screwdriver to open the free stroke screw approximately 2 turns from closed. Pump the brake lever again to remove any possible air bubbles. Then close the free stroke screw all the way so that air cannot find its way into the pocket behind the screw. 

11. Remove Bleed Cup and Install Bleed Lever Cap Screw

• Once you seem to have removed all of the air bubbles from the brake lever and have a strong lever feel, plug the bleed cup and remove it from the brake lever. Dispose of the mineral oil appropriately. Use a 2.5mm Allen key and install the bleed lever cap screw sealing the brake system. 

12.  Clean Brake Lever And Readjust Lever Position

• Grab the degreaser or cleaner one more time and clean off any spilled oil on the brake lever. Any squish in the brake lever feel means that there may be some air left in the brake system. Your bike safety relies heavily on the brake system functioning properly, and if you don't have the necessary tools to get the job done, bring your brakes into a bike shop to ensure they are serviced by a professional. 

This article was written / authored by Max Morgan. Max has been a professional downhill mountain bike racer for the last 10 years, competing in the UCI World Cup downhill series and U.S. Pro GRT series. Having ridden all different kinds of bikes on trails all over the world, Max's experiences being out on the circuit give him a unique perspective on what makes for a quality cycling component. Max also has degrees in Mechanical Engineering and Physics, and so if you don't see out on the trail, chances are he is probably in the garage tinkering on the next project.