Brake Bleeding

Step-by-step hydraulic brake bleeding for Shimano, SRAM, and Magura systems.

Restoring Full Brake Power

Hydraulic brake performance degrades as air enters the system — micro-bubbles compress under lever input, creating sponginess and inconsistent power modulation. Bleeding removes trapped air and replaces degraded fluid to restore firm lever feel and predictable stopping power. Each manufacturer uses a different fluid type and bleed procedure. Mixing fluid types or using incorrect technique will damage seals and pistons.

Why Proper Bleeding Matters

Properly Bled Brakes

•Firm, consistent lever feel with zero sponginess
•Full power modulation — precise control from feathering to full lockup
•No lever fade on long descents where heat builds in the system
•Predictable bite point position that stays constant across conditions

Air-Contaminated System

•Spongy lever feel — reduced confidence in steep or technical terrain
•Wandering bite point that changes with temperature and lever angle
•Reduced power — longer stopping distances in emergency situations
•Degraded fluid absorbs moisture (DOT) or breaks down thermally, accelerating seal wear

System Comparison

System	Fluid Type	Primary Method	Service Interval	Key Consideration
Shimano	Mineral Oil (Shimano-specific)	Gravity / Funnel bleed	Every 6–12 months	Non-hygroscopic — longer fluid life, simpler procedure
SRAM	DOT 5.1 (glycol-based)	Syringe-to-syringe	Every 6 months	Hygroscopic — absorbs moisture over time, higher boiling point when fresh
Magura	Royal Blood (Magura mineral oil)	EBT (Easy Bleed Technology)	Every 6–12 months	Proprietary connections — use Magura-specific bleed kit

Fluid Compatibility Warning

NEVER mix fluid types. DOT fluid in a mineral-oil system destroys seals within hours. Mineral oil in a DOT system reduces boiling point and causes brake fade under heat. When in doubt, check the lever body — most have the fluid type stamped on the reservoir cap.

Shimano Bleed Procedure

Gravity/funnel method — mineral oil

Shimano bleed kit (funnel + stopper), Shimano mineral oil, 7 mm wrench, bleed block, clean rags, isopropyl alcohol

1Preparation

•Remove wheel and install bleed block between pads (critical — prevents pistons from contacting)
•Clean the lever reservoir area and caliper bleed port with isopropyl alcohol
•Level the bike so the lever reservoir is the highest point in the system
•Remove the lever bleed port screw and attach the bleed funnel

2Fill & Purge

•Fill the funnel half-full with fresh Shimano mineral oil
•Open the caliper bleed nipple (7 mm wrench) — old fluid and air will gravity-drain into a catch bottle
•Pump the lever gently 10–15 times to push fluid through. Tap the hose and caliper to dislodge bubbles.
•Continue until fluid runs clear with zero bubbles exiting the caliper bleed nipple

3Finalize

•Close the caliper bleed nipple — snug, not gorilla-tight (4–5 Nm)
•With funnel still attached, pump lever 10 times — watch for bubbles rising into the funnel
•Flick the hose and lever body to release any trapped micro-bubbles
•Close the funnel stopper, then remove the funnel. Replace the lever bleed port screw with new O-ring
•Wipe all spilled fluid immediately — mineral oil contaminates brake pads and rotors

SRAM Bleed Procedure

Syringe-to-syringe method — DOT 5.1

SRAM bleed kit (2 syringes + fittings), DOT 5.1 fluid (SRAM or Avid branded), T10 Torx, bleed block, gloves, clean rags

1Preparation

•Remove wheel and install bleed block — SRAM pistons advance easily and can pop out
•Remove the caliper bleed port screw (T10 Torx) and thread in the caliper syringe (half-full, bubble-free)
•Remove the lever bleed port screw and thread in the lever syringe (¼ full, bubble-free)
•CRITICAL: Wear gloves — DOT fluid strips paint and is a skin irritant

2Push-Pull Cycle

•Push the caliper syringe slowly — fluid travels up through the hose to the lever syringe
•Pull the lever syringe gently to assist flow — watch for air bubbles in the syringe
•Reverse direction: push from the lever syringe, pull from the caliper syringe
•Repeat push-pull cycles 10–15 times. Tap the hose and caliper with a wrench handle to dislodge trapped air.
•Continue until both syringes show zero bubbles in the fluid

3Pressure Cycle & Close

•With the lever syringe closed (clamp the hose), push in slightly on the caliper syringe to pressurize the system
•Pump the brake lever 10 times against the pressurized system — this forces any remaining micro-bubbles toward the lever
•Open the lever syringe — collect any remaining bubbles
•Close the lever syringe, remove it, and immediately re-install the bleed port screw (0.8 Nm with new O-ring)
•Close the caliper syringe, remove it, and re-install the caliper bleed port screw

DOT Fluid Handling

DOT 5.1 is hygroscopic — it absorbs atmospheric moisture from the moment the bottle is opened. Use a fresh, sealed bottle for each bleed. Discard opened bottles after 6 months. Store sealed bottles upright in a cool, dry location.

Magura Bleed Procedure

EBT (Easy Bleed Technology) — Royal Blood

Magura EBT bleed kit (syringe + adapter), Magura Royal Blood mineral oil, bleed block, clean rags

1Preparation

•Remove wheel and install bleed block between pads
•Level the bike — lever reservoir at the highest point
•Remove the lever reservoir cover (T10 or T25 depending on model)
•Attach the EBT syringe adapter to the caliper bleed port

2Flush & Bleed

•Fill the EBT syringe with fresh Royal Blood — remove all air from the syringe first
•Push fluid slowly from the caliper upward — old fluid and air exit through the lever reservoir
•Continue pushing until fluid flows clean and bubble-free from the reservoir
•Tap the lever body, hose, and caliper firmly with a wrench handle to release trapped bubbles
•Pump the lever 15–20 times with the reservoir open — watch for final bubbles rising

3Finalize

•Top off the lever reservoir to the fill line — overfilling causes pressure build-up in heat
•Reattach the reservoir cover with a new O-ring seal
•Remove the caliper syringe adapter and re-install the bleed port screw
•Wipe all surfaces clean and check for leaks at all connection points

Magura Short Service Bleed

If lever feel is slightly soft but fluid looks clean, a short bleed may suffice: open the lever reservoir, pump the lever 20–30 times to push micro-bubbles out, then top off and reseal. Takes 5 minutes and avoids a full system flush.

Pad & Rotor Contamination

Any brake fluid on pads or rotors means compromised braking. Prevention and recovery:

•Always install the bleed block before bleeding — this is non-negotiable
•Cover rotors with a clean cloth or bag during the bleed procedure
•Contaminated pads: discard metallic pads immediately. Resin pads can sometimes be saved — sand the surface with 120-grit, then torch (heat) the pad surface to burn out absorbed oil
•Contaminated rotors: clean with isopropyl alcohol (90%+) and a lint-free cloth. Multiple passes.
•If braking remains compromised after cleaning, replace both pads and rotor — fluid penetrates the friction material

Troubleshooting

Still Spongy After Bleeding

Air remains trapped in the system:

Re-bleed with the caliper at the lowest point and lever at the highest — gravity helps
Tap the caliper, hose, and lever body firmly during the bleed — bubbles cling to internal surfaces
For SRAM: add extra push-pull cycles and rotate the caliper between each pass
Check for a leaking lever piston seal or caliper bleed port O-ring — air re-enters through worn seals

Lever Pulls to Bar

The system has a large air pocket or a leak:

Inspect all connection points for fluid weeping — tighten or replace O-rings
Check the lever piston for scored or damaged surfaces — scored pistons leak internally
Verify the pads have material — worn pads require excessive piston travel
Perform a full bleed from scratch — partial bleeds can trap air in caliper piston bores

Brake Squeal After Bleeding

Typically fluid contamination on pad or rotor surface:

Inspect pads for glossy or discolored friction surface — discard if contaminated
Clean rotor with isopropyl alcohol — both sides, multiple passes
Bed in new pads: 10 stops from moderate speed, increasing force progressively
If squeal persists with clean rotor and new pads, check caliper alignment — uneven pad contact causes vibration

Pro Tips

Bleed on a Schedule

Don't wait for sponginess. DOT systems absorb moisture continuously — water content above 3% drops the boiling point below safe limits for alpine descents. Bleed every 6 months regardless of feel.

Set Bite Point After Bleeding

Most Shimano (Servo Wave) and Magura brakes allow bite-point adjustment via a dial or reach screw near the lever pivot. Dial this in after a fresh bleed — the firm lever feel gives you the most adjustment range.

Post-Descent Cooling

After long descents, don't immediately squeeze the lever while stationary — heat soaked in the caliper boils fluid and creates vapor lock. Roll gently and pump the lever to circulate cooler fluid from the hose.

Storage Orientation

Store bikes upright or with the lever above the caliper. Hanging a bike upside-down for extended periods can migrate air bubbles into the caliper body, creating sponginess the next ride.

Don't Mix Brake Systems

Running Shimano front and SRAM rear (or vice versa) means two bleed kits, two fluid types, and two maintenance schedules. Stick to one manufacturer per bike for simplicity.

Use Manufacturer Fluid

Generic mineral oil varies in viscosity and seal compatibility. Shimano mineral oil, Magura Royal Blood, and SRAM DOT 5.1 are formulated for their specific seal compounds. Third-party alternatives risk long-term seal degradation.

Brakes Bled, Confidence Restored

Clean fluid, zero air — your brakes are ready for anything. Maintain a regular bleed schedule, use the correct fluid, and your hydraulic system will deliver consistent, powerful stopping for thousands of kilometers.

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