Bleeding addresses air in a hydraulic brake system; it is not a cure for every weak-brake symptom. Identify the installed brake and its required fluid before service. Both 80V brakes are hydraulic, but kit-specific steps still belong with the actual hardware.
Component Instructions Come First
Confirm the fluid and procedure for the installed brakes. The MOKE upgrade guide keeps its caliper-specific bleeding and mounting details. The shared methods below do not establish every rear-caliper service detail.
Confirm the fluid specified on the installed 80V brake hardware, particularly on an aftermarket system.
For symptom diagnosis, see ONYX Brake Diagnostics . Retain the caliper-removal and spacer instructions in the relevant front or rear upgrade procedure.
Brake Fluid
The ONYX RCR uses DOT 3 or DOT 4 brake fluid only.
Using the correct fluid type is critical for seal compatibility, moisture handling, and consistent braking performance.
Fluid Types
| Fluid Type | Base | Typical Dry Boiling Point | Notes |
|---|---|---|---|
| DOT 3 | Glycol | ~205°C / 401°F | Stock fluid |
| DOT 4 | Glycol | ~230°C / 446°F | Higher boiling point |
| DOT 5.1 | Glycol | ~260°C / 500°F | Compatible but not used in ONYX systems |
| DOT 5 | Silicone | ~260°C / 500°F | Not compatible |
Compatibility Matrix
| From \ To | DOT 3 | DOT 4 | DOT 5.1 | DOT 5 |
|---|---|---|---|---|
| DOT 3 | ✓ | ✓ | ✓ | ✗ |
| DOT 4 | ✓ | ✓ | ✓ | ✗ |
| DOT 5.1 | ✓ | ✓ | ✓ | ✗ |
| DOT 5 | ✗ | ✗ | ✗ | ✓ |
Key Rules
- The bike normally ships with DOT 3
- DOT 3 and DOT 4 can be safely mixed
- DOT 5.1 should not be used in ONYX systems despite compatibility
- DOT 5 must never be used or mixed
Why DOT 5.1 Is Not Used
Although DOT 5.1 is glycol-based and technically compatible:
- provides no meaningful performance gain in this system
- more sensitive to contamination and moisture in real-world use
- unnecessary for the thermal limits of ONYX braking systems
Why DOT 5 Is Not Compatible
DOT 5 is silicone-based, unlike DOT 3, DOT 4, and DOT 5.1 which are glycol-based.
This creates several problems:
- does not absorb moisture (water pools inside the system)
- increases corrosion risk
- incompatible with seals designed for glycol fluids
- cannot mix with DOT 3, DOT 4, or DOT 5.1
Using DOT 5 in an ONYX system can lead to brake failure and long-term damage.
Practical Recommendation
For ONYX use:
- DOT 3 = acceptable and stock
- DOT 4 = preferred upgrade for higher heat tolerance
- DOT 5.1 = do not use in ONYX systems
- DOT 5 = do not use under any condition
Critical Warnings
- Do not use DOT 5
- Do not use DOT 5.1 in ONYX systems
- Do not mix silicone and glycol fluids
- Do not allow oil or grease near pads or rotor
- Do not operate with low fluid levels
Brake Bleeding (Hydraulic System)
When to Bleed Brakes
- soft or spongy lever
- inconsistent braking feel
- after replacing brake fluid
- after opening the brake system
This system is highly sensitive to air; even small amounts will significantly reduce braking performance.
Platform Notes
- 80V ONYX -> bleed front and rear brakes
Tools Required
- DOT 3 or DOT 4 brake fluid
- Clear hose
- Catch container
- 8mm wrench
- Clean cloth
Brake Bleeding Procedure
- Keep the bike upright and stable
- Turn handlebars so the reservoir is level
- Remove reservoir cap
- Attach hose to bleed valve
- Squeeze and hold brake lever
- Open bleed valve briefly
- Close valve before releasing lever
- Release lever
- Repeat until no air bubbles appear
- Maintain fluid level - do not let it run dry
Critical Bleeding Rules
- Never release the lever while the bleed valve is open
- Never allow the reservoir to run dry
- Use only DOT 3 or DOT 4 fluid
- Clean spilled fluid immediately
Completion Check
- Lever feels firm
- No visible air bubbles
- Consistent braking pressure
- Reservoir filled to proper level
If proper lever feel cannot be restored, inspect for leaks or internal seal failure.
Alternative Bleeding Methods
Vacuum Bleeding
- Uses a vacuum pump at the caliper
- Pulls fluid through the system
Notes:
- May pull air past bleed valve threads
- Ensure tight hose seal
- Not always reliable for final bleed
Reverse Bleeding
- Fluid is pushed from caliper to reservoir
- Forces air upward
Notes:
- Tap brake line and caliper lightly to release trapped air
- Monitor reservoir level closely
- Stop if fluid rises too quickly
Recommendation
- Use standard bleeding method first
- Use alternative methods only if needed
- Always finish with a manual lever bleed