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How-to guide

When and how to bleed hydraulic disc brakes

When a hydraulic brake needs a bleed, why mineral oil and DOT fluid never mix, the general bleed flow from Shimano and SRAM, and where to find your brake's official procedure.

Last edited Nov 8, 2026 by Pedalwise team Edit History Add a subpage

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Difficulty
Difficult
Time
45 to 90 minutes

Tools

Parts

  • Brake fluid (mineral oil or DOT, exactly as your brake specifies)

Hydraulic disc brakes push fluid through a sealed hose. Air or old fluid in that system makes the brake soft and unreliable, and a bleed replaces the fluid and pushes the air out. This is an advanced job. Park Tool calls bleeding an advanced procedure that needs a solid understanding of the brake system (Park Tool). This page explains when a bleed is needed and the general flow, then points you to the official procedure for your brake. Follow that procedure, not this summary, when you do the work.

Don't ride a bike with weak or unreliable brakes. Shimano says that if the lever feels sluggish or gives no resistance, stop using the brakes and see a professional (Shimano dealer manual).

E-bikes are usually heavier than regular bikes and speed up quickly, so Bosch advises learning how yours handles and brakes, and checking the brakes regularly (Bosch eBike guide).

When a bleed is needed

  • The lever feels soft or spongy. Air compresses, so the lever loses firmness (Park Tool).
  • The lever pulls all the way to the bar, which can mean air, contamination or a leak (Shimano maintenance tips).
  • The fluid is dirty (Park Tool).
  • The hose was cut or replaced, which lets air in (SRAM bleed manual).
  • On a schedule. SRAM recommends bleeding at least once a year, and more often for frequent or hard riding (SRAM user manual).

Mineral oil and DOT fluid never mix

  • Each brake is designed for one fluid. Shimano brakes take only Shimano mineral oil (Shimano dealer manual). SRAM hydraulic brakes take only DOT 4 or DOT 5.1, and SRAM says not to use mineral oil or any other fluid (SRAM bleed manual).
  • Park Tool warns never to put mineral oil in a DOT brake or the reverse, and never to share a bleed kit between the two, because mixing can damage parts and cause brake failure (Park Tool).
  • DOT fluid is corrosive, irritates skin and eyes, and damages paint. Wear gloves and eye protection and wipe spills quickly (Park Tool, SRAM bleed manual).
  • Use oil from a freshly opened bottle and don't reuse drained oil (Shimano dealer manual).

Photo needed: A mineral oil bottle and a DOT fluid bottle side by side with their labels showing. Add one

Find the official procedure for your brake

  • Shimano: the dealer manual for your brake on si.shimano.com, such as DM-MBBR001. Park Tool's Shimano bleed guide walks through it with photos.
  • SRAM: the SRAM DOT bleed manual. First check whether your caliper has a Bleeding Edge port, because the steps differ (SRAM bleed manual). Park Tool's SRAM bleed guide covers calipers without Bleeding Edge.
  • Other brands: use your brake maker's own manual. Park Tool says to consult the maker's model specific information if you are unsure or the bleed isn't working (Park Tool).

General bleed flow

1Get the right fluid and kit

Match the fluid and bleed kit to your brake, as above. Cover the floor and keep rags close (Park Tool).

2Prepare the bike

  • Note your lever reach settings so you can restore them, remove the wheel and pads, and fit a bleed block in the caliper (Park Tool).
  • Keep the pads clean and away from fluid. SRAM says fluid on pads or rotors reduces braking (SRAM bleed manual).
  • Set the lever at the angle your manual gives. Shimano lists different lever positions for different models (Shimano dealer manual).

Photo needed: Caliper with the pads out and a bleed block in place. Add one

3Push fresh fluid through

  • Shimano style: fit the funnel at the lever, connect a filled syringe at the caliper bleed nipple, open it, and push fluid up until no bubbles appear (Shimano dealer manual, Park Tool).
  • SRAM style: syringes at both the caliper and lever, pushing fresh fluid through and using push and pull cycles to draw out bubbles (Park Tool).

Photo needed: Syringe attached to the caliper bleed port with fluid moving up the hose. Add one

4Clear air at the lever

Shimano's method tilts the lever about 30 degrees each way and repeats until no bubbles come out (Shimano dealer manual). SRAM's method purges air at the lever syringe and works the lever until no bubbles remain (Park Tool).

5Close up and clean

  • Refit and torque the bleed screws to the values in your manual, which vary by model (Shimano dealer manual).
  • Clean the lever and caliper with isopropyl alcohol, remove the bleed block, refit pads and wheel, and pump the lever (Park Tool).

6Check for leaks and test

  • Check for leaks after bleeding (Shimano dealer manual).
  • Before riding, work the lever a few times to confirm it is normal. If it feels sluggish or gives no resistance, stop using the brake and see a professional (Shimano dealer manual).
  • Recenter the caliper if the pads rub (Park Tool).

7Dispose of old fluid

Follow local rules. SRAM says never pour fluid down a drain, onto the ground or into water (SRAM bleed manual).

When to take it to a shop

  • You don't know which fluid your brake uses, or you don't have the matching kit.
  • Worn or rubbed through hoses. Shimano says replace them and rebleed, or have a shop do it (Shimano maintenance tips).
  • The lever is still soft after a bleed, or you see a leak. Dealers can bleed brakes for you (SRAM troubleshooting).
  • Any doubt at all. See when to call a pro.

Sources

Videos

How to Bleed Hydraulic Brakes: Shimano® Reservoir Style from Park Tool: A full bleed of a Shimano mineral oil brake with a funnel at the lever and a bag at the caliper.
How to Bleed Hydraulic Brakes: Tektro® & TRP® Flat Bar and Drop Bar Levers from Park Tool: Covers the Tektro and TRP brakes fitted to many e-bikes, from setting up the syringes to the final lever check.

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