Over time, Shimano hydraulic brake systems take in air. Unlike the incompressible fluid in the bike’s brake lines, the unwanted air bubbles are made up of compressible gas and can easily reduce the braking performance dramatically.
Bleeding Shimano brakes is a bike maintenance practice that helps eliminate air bubbles and deteriorated oil from the brake system. It is necessary to ensure that the brakes are stopping the bike as they should – this helps you stay safe on the biking trails. In this guide, we will show you how to bleed Shimano brake.
A 10-Step Guide on How to Bleed Shimano Brake
1. Gather the Necessary Tools
When bleeding Shimano brakes, you will need to have the following tools within easy reach:
- Mineral oil
- Flat bladed screwdriver or piston press
- Shimano bleed cup
- 2.5mm, 3mm, & 4mm Allen key
- 7 mm spanner/open wrench
- Shimano bleeding block
- Bleeding hose
- Philips head screw driver
- Oil Catch bottle
- Tire levers
- Rags for cleaning up
2. Mount Your Bike to a Work Stand
To make your work easier when bleeding Shimano brakes, you will need to mount your mountain bike to a work stand. If you do not have a work stand, find somewhere where your budget road bike will remain stable and upright throughout the bleeding process.
Once your commuter bike is in a reliable workplace, use your 4mm Allen key to raise the brake levers to a point where they are parallel to the ground. This will help you keep the brake oil from spilling on the levers and onto the ground. Tighten down your brake lever bar clamp in the parallel position.
Remove the Brake Pads
Depending on the brakes you intend to bleed, remove either the rear or front bike wheel. Our steps on how to change a tire should help you with removing the wheel. Set the wheel aside for now.
Next, remove the cotter pin and then use the 3mm Allen key to remove the bolt that secures the bike’s brake pads to the brake caliper. Be sure to set the brake pads out of your way for now – this will help you avoid contaminating them with the mineral oil when you bleed Shimano brake. If your brake pads get contaminated, they will lose their stopping power – this can compromise your safety on the biking trips.
3. Install the Bleed Block and the Bleed Cup
Using your tire levers, press out the caliper pistons as necessary. Avoid using a metal screwdriver since you might damage or even crack the ceramic pistons.
Place your Shimano bleed block into your brake caliper and then secure it in place using the bolt that holds your brake pads in place. Use the 3 mm Allen key to tighten.
Once the bleed block is in place, you will need to place the bleed cup on the brake lever. Using the 2.5mm Allen key, remove the brake lever cap screw present on top of the lever’s reservoir. Be cautious to avoid losing the O-ring available at the base of the cap screw.
Next, fill your Shimano bleed cup with the Shimano mineral oil and then screw it to the brake lever. Be extra careful to avoid cross-threading your bleed cup into the brake lever. Since the threads are made of plastic, they can get damaged quite easily if caution is ignored.
Make sure that a rubber O-ring is present at the bleed cup’s base to ensure a perfect seal. Without this seal, air may get introduced into the brake line.
4. Attach an Oil Catch Bottle to Your Brake Caliper
Press a rubber hose (oil line) onto the bleed port fitting close to the top of your caliper bolt. Be sure to push this line to fit so that no air can get in and no mineral oil can get out.
Here, you will need to attach the oil catch bottle to your oil line. However, you can also allow the oil line to just rest in your catch bottle. Just make sure that the oil from your brake system can drip into your catch bottle.
5. Open the Brake System
To bleed Shimano brake, you will need to open the brake system at both the brake lever and caliper. Pull the plug that sits in the bleed cup’s center to allow the brake oil to start following into your brake’s lever reservoir.
Using your 7mm wrench (spanner), open the bleed port at the brake caliper about an eighth of a turn. Now that both ends of your brake system are open, the brake oil should start flowing and dripping into your catch bottle.
Allow the dirty mineral oil to fill your catch bottle until clean and fresh oil begins to come out of the brake caliper. You will now that all the nasty oil has drained from the brake system when the clean oil starts flowing out.
Continue topping off mineral oil in your bleed cup. The key here is to avoid introducing air into your brake system through the open end of your brake system. If the steady oil dripping starts to slow down or stops, push the fluid through the line using your bike’s brake lever.
When you pull your brake lever and hold it closed, the oil should push through the line and out through the brake caliper. However, releasing the lever will create a vacuum at the brake caliper and you do not want this to happen.
For this reason, pull your brake lever and hold it closed, tighten the brake’s bleed port at the caliper using the 7mm wrench, release the lever blade, and then open your bleed port again. Repeat this several times – about 4 times – to continue pushing the oil through the caliper.
6. Close the Brake Caliper Bleed Port
After bleeding Shimano brakes, the next step is closing the caliper bleed port. To do this, you will need to use your 7mm open-ended wrench.
Remove your oil catch bottle and line from your brake caliper. Dispose of the used dirty oil appropriately.
7. Clean Your Brake Caliper and Install Brake Pads
It is not uncommon for the mineral oil to spill on the brake caliper. If this happens, you will need to clean your bike. Use a degreaser or a cleaner to clean off your brake caliper thoroughly before installing the brake pads.
As noted earlier, you must keep the brake pads away from the location where you intend to bleed Shimano brakes – this keeps them away from the mineral oil which can easily reduce their effectiveness. You will also need to handle the brakes with oil-free hands during their installation.
Use a 3mm Allen key to secure the brake pads back in place on your hardtail mountain bike – do not forget the smaller cotter pin. Next, place the wheel back on your bike, tighten the axle appropriately, and then adjust the gears as needed.
8. Cycle the Brake Lever Blade
At this point, you should be through with all the work at the brake caliper. Now, you will need to proceed to the lever bleed to get rid of the existing bubbles that might be trapped in your brake line.
With your bleed cup approximately 50% full, pump your bike’s brake lever repeatedly and then watch for air bubbles that come up to the top. Using your 4mm Allen key, loosen your brake handlebar clamp and position your break up and down from the parallel to retrieve extra bubbles that might be in the brake system. Take precautions to avoid spilling mineral oil or allowing air through your bleed cup.
Air bubbles are often trapped in the brake lever intricacies. Using the Philips head screwdriver, open the stoke screw about 2 turns from closed. Pump your brake lever again to get rid of any possible air bubbles. Next, close the free stoke screw all the way so that air can’t find its way into the pocket present behind the screw.
9. Remove the Bleed Cup and Readjust the Lever Position
Once you remove all the air bubbles from your brake lever and your lever has a strong feel, unplug your bleed cup. If necessary, dispose of the mineral oil appropriately. Using the 2.5mm Allen key, install your bleed lever cap screw to seal the brake system.
Next, grab a good cleaner or degreaser and clean off any spilled oil on your brake lever. Readjust the lever position and then take your college bike for a ride to make sure that everything is working as it should.
Globo Surf Overview
If you suspect your brake mineral oil has deteriorated or air has been introduced to the brake system, bleeding your hydraulic brakes can help improve your safety on the road.
Bleeding Shimano brakes is a fairly simple procedure and one that a bike owner shouldn’t be intimidated by. Armed with the right tools and detailed instructions that are suited to your bike, you should be able to bleed Shimano brake at home.