Animated service guide
Dirt Bike Brake Fluid Flush, Animated
Brake fluid soaks up water over time, and wet fluid boils at a much lower temperature. A flush pushes the old fluid out through the caliper bleeder with fresh fluid from a sealed bottle until clean fluid with no bubbles comes out. Honda says fluid replacement needs mechanical skill, so take your time and don’t ride until the lever is firm.
The animated guide loads here. Every step is also written out below.
Looking for the full article? How To Bleed Dirt Bike Brakes (And How Hydraulic Brakes Work) covers this job in depth. This page is the animated, step-by-step version used in the MotoMind app.
Before You Start
Tools
- Box-end wrench for the bleeder
- Clear hose that fits the bleeder snugly
- Catch bottle
- Screwdriver for the reservoir cover
- Rags
- Gloves and safety glasses
Parts And Supplies
- A fresh, sealed bottle of the fluid type on your reservoir cap
- Water to rinse spills
Safety
- Brake fluid strips paint and plastic. Cover the tank and fender and rinse spills with water right away.
- Brake fluid is harmful to skin and eyes. Wear gloves and safety glasses.
- Never reuse fluid that came out of the system.
Step By Step
Prep and open the reservoir
Get a fresh, sealed bottle of the fluid your manual names. Cover the tank and fender with rags. Turn the bars so the reservoir sits level, wipe the cap clean, then remove the cover and rubber membrane. Check the membrane for cracks.
- Screwdriver
- Rags
Brake fluid type Bike Spec Source KTM / Husqvarna / GASGAS DOT 4 or DOT 5.1 KTM 450 SX-F 2024 owner’s manual, PDF p. 102 and 168 Yamaha YZ250F / YZ450F DOT 4 Yamaha YZ250F 2026 owner’s service manual, p. 2-5 Use the grade printed on the reservoir cap or in your manual. Never put silicone DOT 5 in a DOT 4 or 5.1 system.
Careful. Never use silicone DOT 5 in a DOT 4 or DOT 5.1 system. They don’t mix.
Shop tip. Many mechanics suck most of the old fluid out of the reservoir with a clean syringe, wipe the bottom and refill with fresh before they start. Less old fluid has to pass through the system.
Fit the bleed hose
Pull the rubber cap off the caliper bleeder. Put the box-end wrench on the bleeder first, then push a clear hose snugly over it and run it into a catch bottle. The clear hose lets you see bubbles and the fluid color.
- Box-end wrench
- Clear hose
- Catch bottle
Squeeze and hold the lever
Squeeze the lever a few times to build pressure, then squeeze and hold it. Keep holding while you open the bleeder in the next step.
Crack the bleeder
Open the bleeder just enough for fluid to flow. Old fluid and any air go into the hose, and the lever moves toward the bar.
- Box-end wrench
Close it, then let go
Close the bleeder before the lever reaches the bar, and only then release the lever. Let go with the bleeder open and the master cylinder sucks air back in through the bleeder.
Careful. The order matters every time. Close first, then release.
Keep the reservoir topped up
Each cycle drops the level. Top up with fresh fluid every few pulls and never let it run dry. If it empties, air gets into the master cylinder and you start over.
- Brake fluid
Careful. Keep water out of the reservoir. Yamaha warns water lowers the boiling point and can cause vapor lock.
Repeat until it runs clean
Repeat squeeze, open, close, release. Watch the hose. You are done when the fluid coming out looks as clean as the fluid in the bottle and has no bubbles. It can take dozens of cycles.
Shop tip. Yamaha says that if bleeding is hard, let the fluid settle for a few hours and bleed again once the tiny bubbles in the hose have gone.
Tighten the bleeder, set the level
With the lever firm, close the bleeder snugly, pull the hose and refit the rubber cap. Set the reservoir to the mark with fresh fluid, refit the membrane and cover, and rinse any spill with water. Throw the old fluid away.
- Box-end wrench
- Brake fluid
Bleed screw torque Bike Spec Source Yamaha YZ250F / YZ450F 5 Nm (3.7 lbf ft) Yamaha YZ250F 2026 owner’s service manual, p. 3-28 Snug the bleeder gently. It is a small screw in an aluminum caliper and strips easily. Check your manual for the value.
Do the rear, then test
Bleed the rear the same way, using the rear reservoir and the bleeder on the rear caliper. Then pump both brakes. Each must feel firm and stop at the same point every time. Test at walking pace before you ride. If the lever is still soft, there is still air, so bleed again.
How often to change it Bike Spec Source KTM / Husqvarna / GASGAS, race or enduro Every 90 h or 24 months KTM 450 SX-F 2024 owner’s manual, PDF p. 40; same on the enduro models. KTM 2026 XC-W OM, PDF p. 54; KTM 450 XCF-W 2025 OM, PDF p. 53; Husqvarna TE 250/300 2026 OM, PDF p. 54 Yamaha YZ250F / YZ450F (race) Every year Yamaha YZ250F 2026 owner’s service manual, p. 3-4 Honda CRF250R / CRF450R race, CRF450X and CRF250F trail Every 2 years Honda CRF450R 2025 owner’s manual, PDF p. 44 (note 2); CRF450X 2025 OM, PDF p. 46 to 47; CRF250F 2025 OM, PDF p. 53; CRF450RL Off-Road Handbook, PDF p. 37 Check your manual. Racers often change it far more often than the schedule.
Careful. Never ride on a soft lever. Yamaha says to check brake operation after every bleed.
Sources
Log It And Know When It Is Due Next
MotoMind logs engine hours and every service job with notes, parts and cost, and shows each task as upcoming, due or overdue. Available to download on iOS.
