Essential Guide to Bleeding Hydraulic Bike Brakes at home

Over the past few years bikes became more complex, integrated handlebars, cables routing through headsets, specific bearing setups and hydraulic brakes. Modern hydraulic brakes are advanced systems but not that difficult to service and can be fixed relatively fuss free, it takes following the procedures and extra care with corrosive oils . For some this task is too much, as it is an advanced service, but for someone with good mechanical skills and some time for researching the process it can be completed at home and a rewarding job done. Tools can be bought for around $50 and you can do the job in a couple of hours.

How often do I need to bleed my brakes and what are the signs?

For most people the time to bleed brakes comes when the brakes don’t feel right. They feel spongey or the lever moves too much and doesn’t apply power. Another tell tale sign maybe that the lever will be slow to return to original non position. Modern brakes with normal use only need bleeding every 2-3 years, because the technology is that good. If you mountain bike frequently you may find you need to service once every two years.

Why ? and the fundamentals

Think of the braking system as a sealed tube full of oil. That tube runs from your lever to your caliper at your wheel, this a sealed system which supposed to have no air or water in the tube. But, because oil attracts moisture, over time that (air or water) can seep in through seals and cause the spongey feeling and lack of response. By bleeding the brakes you are doing two things, adding fresh oil and removing air.
Bleeding simply ensures there are no air bubbles caught inside the tube of oil. The air bubbles are removed by connecting two syringes of oil, one at the caliper and one at the lever, pressurizing the system and letting the bubbles rise up and out of the oil into the tops of the syringes instead of your brake hose.

Are Road, Gravel, Mountain bike hydraulic brakes different ?

In principle the same same, in practicality the use similar tools and similar procedures but are not 100% similar. As everything in the world of cycling the technicalities differ, between manufacturers and often mountain bikes need more stopping power so the engineering of such components will be different, but the principles are the same. Bottom line, check your manufacturer and specific model before going further. At the initial parts its useful to know if you have a Shimano (Mineral Oil) or Sram (DOT Fluid system).

What do tools need?

You need bleed kit tools and fluid that match your brand of brakes, most common brands are Shimano or SRAM. Of course there are inexpensive tools that will make the job more difficult but the job will be less expensive at a risk of going wrong, you can find these on Amazon and are typically $15-$30, then there are comprehensive tools that are a little more expensive but will do the job correctly first time and have the correct fittings, so you won’t be frustrated and start a job you cannot finish. Honestly, I have used both and for the money difference, I prefer the mid range to better tools. Here are some bleed kits I recommend:
Bleed Kit SRAM –
SRAM 5.1 Fluid*
Bleed Kit Shimano
Shimano Mineral Fluid*
* – sometimes its easier to buy the fluid local at a bike shop, as shipping can be an issue.

Along with the Fluid and Tools, it’s important to have gloves, protective eyewear and Rubbing alcohol (isopropyl alcohol) for cleanup. The brake fluid used in SRAM products is dangerous and corrosive, so be very careful not to spill and to immediately wipe and use alcohol if you do.

Nitrle or Latex Gloves
Alcohol
Protective eyewear

Setup Importance!

A clean, fuss free setup that is near the bike will help you avoid spills and get the job done quicker.

Above is a picture of my last setup. I was bleeding SRAM MTB brakes. Note: I have two separate areas, one for my brake pads and fixing parts, and one for the bleed syringes and oil, so things don’t get contaminated.. The area is clean and I only have minimal tools that I will need. The plastic tyre lever is used to spread (retract into body) the caliper pistons to allow space for bleed block. Another thing to note is that I have a small container of new brake fluid, if you have a large one, be very careful no to knock it over, I have seen it happen and its a lot of cleanup. What is not shown is alcohol in a spray bottle, gloves and some rags, which are all close to and on the bike.

CAUTIONS!

Brake fluid comes in two types, Mineral Oil- normally used by Shimano and DOT 5.1 Oil normally used by SRAM/AVID. Both types can be absorbed through the skin into the blood, so always wear gloves. Also DOT5.1 can remove paint, so be extra careful. Have extra rags handy and alcohol to clean up.
Eyewear is also recommended to protect from any splashes.

Keep oil away from brakepads. Getting oil on the brakepads is irreversible and you will need to buy new pads. So use clean hands and set pads aside when beeding.

And of course , brakes are important! , so always test your work in a safe flat area and if anything seems suspicious or goes incorrectly, take your bike to a professional mechanic.

TIPS

DO – Follow manufacturers instructions.
DO- Have a small old container to put used fluids in.
DO – Hang some rags on your bars and on the chainstay near your rear caliper or near the fork. Having them handy is essential for small quick cleanups.
DO – If you have a painted bike, always a good idea to cover the top and fork legs when using DOT fluid, as a small spill wills tip paint.
DO – Have good lighting and all your tools laid out.
DON’T – reuse dirty oil.
DON’T – get oil near, or touch brake pads with dirty gloves.
DON’T – mix DOT and Mineral oil. Don’t mix bleed kits, keep DOT for DOT and Mineral for Minerals. Cross contamination can cause issues,

Next – STEP by STEP instructions.

Watch some instructions and find info for your specific bike components -Useful links and video step throughs

Highly recommended videos and resources

SRAM video : https://www.youtube.com/watch?v=DRt-CP2l474
SHIMANO Technical Manuals here : https://si.shimano.com/en/
SRAM Technical Manuals here: https://www.sram.com/en/service/manuals–documents/service-manuals

Not as complete but still worth a look – second reference. Often these are missing essential parts, that may frustrate you.

Here is a recommended SHIMANO video for Road / Gravel setups : https://youtu.be/rVVvrFaVTcM?si=Ii8eIHPeY9t72Xsk
Note: the people in this don’t use gloves, always use gloves, they people seem to misunderstand how bad for health this oil can be, https://www.youtube.com/@bleedzonekits/videos
This one is also great : https://www.youtube.com/@bleedkit/videos

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