Workshop how-tos · 79Bike · Sur-Ron · Talaria
How to bleed the hydraulic brakes on an electric dirt bike
A soft, spongy brake lever, or one that comes all the way back to the bar, almost always means air in the system or tired fluid. Bleeding restores a firm, consistent brake. It is a safety job: if you are not comfortable doing it, let a workshop handle it.
Step zero: identify the fluid
This is the most serious mistake: DOT fluid and mineral oil must never be mixed. DOT fluid in a mineral-oil system (or the reverse) destroys the seals, and the brake can fail. The fluid type is written on the master cylinder reservoir cap or in the manual. If it is unreadable, don't guess: contact us with a photo of the master cylinder.
- DOT 4 / DOT 5.1: hygroscopic (absorbs moisture), attacks paint — wipe up any drop immediately.
- Mineral oil: does not absorb water, but must never be replaced with DOT.
When to bleed
- Spongy lever, travel that changes from one stop to the next.
- After replacing a hose, caliper or master cylinder.
- After a crash where the bike lay upside down for a while (air rises).
- DOT fluid that is dark or roughly more than two years old.
The classic method (lever + bleed nipple)
It works on most electric dirt bike brakes. Principle: push fresh fluid from the reservoir to the caliper, expelling air through the bleed nipple, never letting the reservoir run dry (or you draw air back in). Turn the bars so the reservoir is level and wrap rags around the master cylinder.
If the lever is still soft after bleeding
Tap the hose and caliper lightly to free micro-bubbles, leave the lever zip-tied to the bar overnight, then do a short re-bleed. If that doesn't work: a worn master cylinder piston seal, a hose that swells or glazed pads. See also replacing brake pads.
Tools you need
- The correct brake fluid (DOT or mineral oil, per the cap)
- Clear tubing and a jar
- Ring spanner for the bleed nipple (often 7 or 8 mm)
- Phillips screwdriver (reservoir cover)
- Rags, nitrile gloves, glasses
- Brake cleaner
Step-by-step procedure
- 1
Identify the fluid
Read the type on the reservoir cap (DOT or mineral oil). Never mix the two.
- 2
Protect and prepare
Remove or protect the pads, cover paint and plastics with rags, and turn the bars so the reservoir is level.
- 3
Open the reservoir
Remove the cover and diaphragm and top up with fresh fluid.
- 4
Attach the tube
Push the clear tube onto the caliper bleed nipple and put the other end in the jar.
- 5
Bleed
Squeeze the lever, open the bleed nipple a quarter turn, close it before releasing the lever. Repeat, topping up the reservoir each time, until fluid comes out clear and bubble-free.
- 6
Close up
Tighten the bleed nipple moderately, top up the level, refit the diaphragm and cover.
- 7
Clean and check
Clean any fluid with brake cleaner. Pump the lever: it must feel firm and return briskly. Check for leaks.
- 8
Safe test
Do several stops at very low speed before riding normally.
Useful genuine parts
In stock, shipped in 3–10 business days.
FAQ
I don't know which fluid to use. Does it matter if I get it wrong?+
Yes. The wrong fluid swells or destroys the seals and can cause brake failure. Don't bleed until you have identified the fluid with certainty.
How often should I bleed?+
DOT fluid: roughly every two years, or sooner if the lever becomes spongy. Mineral oil: when symptoms appear or after any work on the system.
Do I need a syringe bleed kit?+
Not with the lever + nipple method, but syringe kits make the job easier and reduce bubbles, especially on mineral-oil brakes.
Key takeaways
Identify the fluid first, never let the reservoir run dry, bleed until the fluid is bubble-free and finish with a very low-speed test. If in doubt, let the workshop do it.
Need a hand?
Our workshop in Toulouse Sud (France) services 79Bike, Sur-Ron and Talaria. Send us a photo or video of the problem.
Related guides
These guides are for information only. If in doubt about a safety-critical part (brakes, steering, wheels), have a professional do the work. Always follow the manufacturer's manual.