Bleeding the Brakes on a 2025 Honda Grom
Shop parts for a 2025 Honda Grom Motorcycle.
What Your Grom's Brake System Looks Like
The 2025 Honda Grom stops on hydraulic disc brakes at both ends. The lever on the right handlebar drives a single front caliper, and the right-foot pedal drives a separate rear caliper fed by its own master cylinder and reservoir. Because those two circuits are completely independent, each one is bled on its own, and a soft front lever tells you nothing about the condition of the rear pedal. Some 2025 Groms are delivered with ABS; if your bike carries that badge, the routine flush described here still happens at the caliper bleeder valves, but the ABS hydraulic unit adds a wrinkle that is covered near the end of this article. The Grom does not use a linked or combined braking system, so you never have to worry about the front lever also pressurizing the rear caliper.
Why and When the Grom Needs a Bleed
Brake fluid is hygroscopic, meaning it pulls moisture out of the air over time, even in a sealed system. That absorbed water lowers the fluid's boiling point, and a fluid that boils under hard, repeated braking creates vapor in the lines — which feels exactly like air and behaves exactly as badly. This is why many riders refresh the fluid on a regular interval whether or not anything feels wrong, rather than waiting for a problem to announce itself.
On the symptom side, watch for a lever that feels spongy or that pulls noticeably closer to the grip than it used to, a rear pedal that travels farther before it bites, or fluid in the reservoir that has gone dark, cloudy, or gritty. A bleed is also mandatory after any work that opened the hydraulic system: new brake lines, a caliper rebuild or replacement, master cylinder service, or a reservoir that ran dry. On a small bike like the Grom, that last one happens more often than people expect, because the reservoirs hold very little fluid and it is easy to pump the level down to nothing mid-job.
Tools and Supplies to Have on the Bench
- Fresh brake fluid of the type printed on your Grom's master cylinder reservoir cap, poured from a sealed container. Fluid that has been open on a shelf for months has already absorbed moisture.
- A box-end wrench that fits the bleeder valve snugly. A box-end grips all the flats and is far less likely to round a bleeder than an open-end wrench.
- A length of clear tubing that fits tightly over the bleeder nipple, plus a small catch bottle to hang it in. Clear tubing lets you actually see the bubbles and the color change.
- Rags or shop towels, and a spray bottle of water for rinsing spills.
- A syringe or turkey baster for pulling the old fluid out of the reservoir.
- The correct driver for the reservoir cap screws.
A one-way check-valve bleeder or a vacuum bleeder makes the job much easier to do alone, since you no longer have to coordinate the lever and the bleeder valve at the same time.
Setting Up and Protecting the Finish
Get the Grom standing securely upright on a stand so it cannot tip while you are working at the bars. Turn the handlebar so the front reservoir sits level before you open it — a tilted reservoir spills. Lay rags over the tank cover, the plastics around the bars, the instrument cluster, and anything else in the splash zone. Brake fluid attacks paint and many plastics on contact, so treat every drip as urgent: wipe it immediately and rinse the area with water. The same caution applies to the rear reservoir, which sits low on the bike where fluid can run onto the frame and swingarm.
Bleeding the Front Brake, Step by Step
- Clean the reservoir cap and the area around it so no dirt falls in, then remove the cap and diaphragm.
- Use the syringe or baster to draw most of the old fluid out of the reservoir. Do not pump it dry — leave enough that no air can enter the master cylinder port.
- Refill with fresh fluid from the sealed container, leaving the level at the upper marking for now.
- Push the clear tubing onto the front caliper bleeder valve and route the other end into the catch bottle, with the bottle positioned so the tubing runs upward before it drops. That keeps air from creeping back toward the caliper.
- Fit the box-end wrench onto the bleeder, then squeeze the front lever firmly and hold it.
- Open the bleeder about a quarter turn. Fluid and air will push out through the tubing, and the lever will travel toward the grip.
- Close the bleeder before you release the lever. Releasing with the valve open draws air straight back into the caliper.
- Release the lever slowly, then check the reservoir level and top it off. Repeat the squeeze-hold-open-close-release cycle until the fluid coming through the tubing runs clean and clear with no bubbles.
- Keep an eye on the reservoir after every few cycles. If it ever drops low enough to gulp air, you have to start over.
If your bike has two front calipers, bleed each one in turn, finishing with the caliper farthest from the master cylinder. The Grom's single front caliper keeps this simple.
Bleeding the Rear Brake
- Open the rear reservoir, remove most of the old fluid, and top it with fresh fluid.
- Attach the tubing and catch bottle to the rear caliper bleeder and fit the box-end wrench.
- Press and hold the pedal, crack the bleeder a quarter turn, then close it before releasing the pedal.
- Repeat, topping off the reservoir as you go, until the fluid runs clean and bubble-free.
Finishing Up and Checking for Leaks
Close the bleeder snugly — firm enough that it will not weep, but never so tight that you crush the seat or round the hex. Fill the reservoir to the correct level marking, reinstall the diaphragm and cap, and wipe down every surface you touched. Then look closely at the bleeder valves and at the banjo fittings at both the master cylinder and the caliper for any sign of weeping. Pump the lever and pedal a few times and recheck. If a fitting is wet, address it before the bike moves.
Testing Before You Ride
The lever and pedal should feel firm and consistent, and should hold pressure without slowly sinking while you keep steady force on them. Spin each wheel by hand to confirm the brakes are not dragging. Then, in a safe open area at low speed, test the brakes gently before riding normally. If anything feels vague, soft, or inconsistent, stop and diagnose rather than riding it out.
When the Job Belongs in a Shop
If the lever will not firm up after several honest bleeding attempts, if it only firms up when you pump it, if bubbles keep appearing no matter how long you bleed, or if fluid is leaking from the master cylinder or caliper, stop and let a professional look at it. On an ABS-equipped Grom, a standard caliper bleed is fine for a routine fluid refresh, but if the reservoir ran dry, or the ABS unit or its lines were disconnected, air may be trapped inside the ABS unit itself. That requires a dealer-level procedure or diagnostic tool, and it is not a home-garage job.
Related Shopping Categories
Shop Brake Fluid for a 2025 Honda Grom Motorcycle.
Shop Brake Lines for a 2025 Honda Grom Motorcycle.
Shop Brake Pads for a 2025 Honda Grom Motorcycle.
Shop Stands for a 2025 Honda Grom Motorcycle.
Shop Brake Tools for a 2025 Honda Grom Motorcycle.
Disclaimer: This guide is provided for general informational purposes only and is not intended to replace your motorcycle's official owner's manual. Always refer to your manufacturer's documentation for model-specific instructions, torque specifications, safety procedures, and maintenance requirements. If you are unsure or inexperienced, consider seeking assistance from a qualified mechanic or technician.
