Hydraulic disc brakes need periodic bleeding to remove air from the system and maintain firm, consistent lever feel. This guide covers what fluid your brakes use, what you’ll need, and a full step-by-step bleeding procedure.
Step 1: Know Your Fluid – Mineral Oil vs. DOT (This Matters)
Before you buy anything or touch your brakes: mineral oil and DOT brake fluid are not interchangeable. Using the wrong fluid will destroy your brake seals. Check your brand against this table first.
| Brand / Groupset | Fluid Type | Specific Product | Notes |
|---|---|---|---|
| Shimano (all models: MT200, XT, XTR, GRX, Tiagra, 105, Dura-Ace) | Mineral oil | Shimano Mineral Oil or Maxima Formula K | Never use DOT fluid — destroys Shimano seals |
| SRAM / Avid (Level, Guide, Code, DB series) | DOT 5.1 | SRAM DOT 5.1 (or quality automotive DOT 5.1) | Older Avid systems may use DOT 4 — check lever body marking |
| Magura (MT series) | Mineral oil (proprietary) | Magura Royal Blood | Royal Blood is mineral oil with anti-corrosion additives — don’t substitute |
| Hayes | DOT 4 or DOT 5.1 | Hayes DOT 5.1 or quality automotive DOT | Check lever body for DOT rating |
| Tektro / TRP | Mineral oil | Tektro Mineral Oil or generic cycling mineral oil | Not compatible with DOT fluid |
| Formula | Mineral oil (proprietary) | Formula Fluid or RO or R1 specific fluid | Check which Formula brake model you have |
Safety: DOT Fluid Hazards
DOT brake fluid (used by SRAM and Hayes) is caustic and will damage:
- Paint and plastic: Any splash on your frame, fork, or brake levers must be wiped off immediately with clean water — left on, it strips paint within minutes
- Skin and eyes: Wear nitrile gloves and eye protection when working with DOT fluid
- Brake pads: Even a small amount on rotor or pads will contaminate them and reduce stopping power significantly — keep fluid away from wheels
Mineral oil (Shimano, Magura, Tektro) is much safer — it won’t strip paint or irritate skin — but still keep it off rotors and pads.
What You’ll Need
- Bleed kit specific to your brand (see below)
- The correct fluid for your brake brand (see table above)
- 2 syringes with tubing (usually included in bleed kit)
- Pad spacer or bleed block (keep caliper pistons in place)
- Allen keys (typically 2.5mm for Shimano lever bleed port, varies by brand) – a cycling multi-tool covers most of these sizes
- T10 or T25 Torx (varies by caliper brand)
- Nitrile gloves and eye protection (especially for DOT systems)
- Isopropyl alcohol and clean rags
Our Pick
After a bleed, worn brake pads are often the next thing holding back braking performance. We've compared the top disc brake pad compounds for Shimano, SRAM, and Magura systems so you can pick the right replacement.
See our top picks →Brake Bleed Kit – Compatible with Shimano, SRAM, Avid, Magura, Tektro, Hayes
How to Bleed Bicycle Hydraulic Brakes: Step by Step
The procedure below applies to most systems. Shimano and mineral-oil brakes use a gravity/syringe method; SRAM uses a similar syringe-to-syringe method. Refer to your brake’s tech doc for brand-specific bleed port locations.
Prepare the work area
Protect your work surface with cardboard or rags — DOT fluid will strip painted surfaces on contact. Remove the wheel. Insert a pad spacer (bleed block) between the brake pads in the caliper — this prevents the pistons from extending while you work. Lay the bike flat or on a stand so the brake lever reservoir is roughly level.
Access the lever bleed port
On Shimano levers: remove the small bleed port plug (usually a 2.5mm hex bolt) at the top of the brake lever body. Insert a syringe filled with fresh fluid into the port. On SRAM: remove the lever reservoir cover (small Phillips or T10 screw). On Magura: remove the bleed screw on the lever clamp. Have a rag ready — old fluid will drip when you open the port.
Access the caliper bleed nipple
Find the bleed nipple on the caliper body — it’s a small bolt (typically 7mm or 8mm hex, or T10 Torx). Attach the second syringe with tubing to this nipple. Do NOT open it yet. Fill the caliper syringe with a small amount of fresh fluid to create positive pressure when you open the nipple.
Purge air bubbles – push fluid through
Open the caliper bleed nipple slightly (1/4 to 1/2 turn). Gently push fluid from the caliper syringe upward toward the lever — this pushes air toward the lever reservoir. You’ll see air bubbles rising through the tubing. Simultaneously, draw the lever syringe back slightly to pull fluid through. Watch for bubbles: they’ll appear as small white spheres in the clear tubing. Continue pushing and pulling slowly until no bubbles are visible in the lever syringe.
Top up and close the system
With no bubbles visible: ensure the lever reservoir syringe is topped up with fresh fluid. Close the caliper bleed nipple (firm but not overtightened — these are small and strip easily). Remove the caliper syringe. Squeeze the brake lever — it should feel firm, not spongy. If it still feels spongy, repeat step 4. When firm: remove the lever syringe and reinstall the bleed port plug.
Clean up and test
Wipe down the lever, caliper, and rotor area with isopropyl alcohol to remove any fluid residue. Remove the pad spacer and reinstall the wheel. Before riding: pump the brake lever 5-10 times to center the pads. Take a slow test ride in a parking lot, applying brakes firmly from low speed. The lever should feel solid and braking should be immediate. If lever still feels spongy after two full bleeding cycles, there may be a seal leak requiring a brake service.
When Do Brakes Need Bleeding?
- Spongy or soft lever feel — the most common sign of air in the system
- Lever pulls to the bar without engaging the brake
- After brake pad or rotor replacement — sometimes air enters during service
- Annual maintenance for bikes ridden regularly in wet conditions (moisture enters the system over time)
- After any brake hose work — cutting, routing, or replacing hoses always requires a bleed
Note: lever feel issues are sometimes caused by brake lever adjustment rather than air in the system. Before bleeding, check whether reach and bite point adjustment resolves the problem — see our guide on adjusting Shimano hydraulic disc brake levers. Bleeding is a separate operation from lever adjustment.
Also: grease is never used in brake systems. If you’re maintaining other bike components and confused about which lubricant goes where, see our bicycle grease guide for the full breakdown.
Frequently Asked Questions
How often should you change bicycle brake fluid?
For most riders: bleed brakes when the lever feel becomes spongy, or as part of annual service if you ride frequently in wet conditions. DOT fluids absorb moisture over time and should be replaced every 1-2 years even if feel seems normal, since moisture absorption lowers the fluid’s boiling point. Mineral oil (Shimano, Magura) doesn’t absorb moisture the same way and typically needs topping up rather than full replacement unless the system was opened.
Can I use automotive DOT fluid in my bike brakes?
Yes, for SRAM, Hayes, and other DOT-compatible systems — high-quality automotive DOT 5.1 fluid works well and is often cheaper than branded cycling fluid. The key requirement is DOT 5.1 (not DOT 5, which is silicone-based and not compatible). Never use automotive DOT fluid in Shimano, Magura, Tektro, or Formula brakes — those use mineral oil and DOT fluid will swell and destroy the seals.
What happens if I accidentally mix DOT and mineral oil?
This is a serious problem. If DOT fluid enters a mineral oil system (or vice versa), the seals will swell and fail. The brake will stop working, often suddenly. If this happens, the brake needs a full flush and seal replacement — not just a bleed. If you suspect a contamination, stop riding and take the bike to a mechanic. Don’t test the brakes on a descent.
My brakes still feel spongy after bleeding twice — what’s wrong?
Persistent sponginess after two bleeds usually indicates: (1) a leaking seal at the lever or caliper — look for fluid weeping from fittings or staining on the hose; (2) a damaged hose with microcracks letting air in; (3) cracked or deteriorated seals inside the caliper pistons. These require component replacement, not just a bleed. Take it to a shop if the issue persists.
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