Bleeding the Brakes on a 2021 Honda Monkey
Shop parts for a 2021 Honda Monkey Motorcycle.How the Monkey’s Brakes Are Set Up
Before you touch a wrench, it helps to know exactly what you are working on. The 2021 Honda Monkey Z125M uses hydraulic disc brakes at both ends — a hand lever on the right bar for the front and a foot pedal on the right side for the rear. Because both systems are hydraulic, both are bled the same way, and both deserve attention when you service the brakes. There is no mechanical drum brake on this bike to adjust instead.
The Monkey is also fitted with an anti-lock braking system. That does not change the everyday bleed you will do at the caliper, but it does change your limits. A routine fluid refresh through the caliper bleeder is a normal home-garage job. If air has found its way into the ABS unit itself — because the reservoir ran dry, or because the unit or its lines were disconnected during other work — the modulator may need a dealer-level procedure or a diagnostic tool to purge properly. Do not try to improvise that part at home.
When a Bleed Is Actually Due
Brake fluid is hygroscopic, meaning it pulls moisture out of the air over time. That moisture lowers the fluid’s boiling point, and a fluid that boils under hard, repeated braking turns to vapor in the lines — which feels exactly like air in the system and shows up as fade when you need the brakes most. That is why many riders refresh the fluid on a schedule even when nothing feels wrong.
On top of the calendar, watch for symptoms. A lever or pedal that feels spongy or soft, a front lever that now comes noticeably closer to the grip than it used to, fluid in the reservoir that looks dark or cloudy rather than clear, or a pedal that sinks slowly while you hold steady pressure all point to a bleed being overdue. Any job that opened the hydraulic circuit — new lines, caliper service, master cylinder work — also requires a bleed afterward before the bike goes back on the road.
Tools and Supplies to Gather
- Fresh brake fluid of the type marked on the master cylinder reservoir cap, from a sealed container. Do not substitute a different type and do not use a bottle that has been open and sitting on the shelf.
- A box-end wrench that fits the bleeder valve snugly. A box-end grips the flats far better than an open-end and is much less likely to round the bleeder.
- A length of clear tubing that fits tightly over the bleeder nipple, plus a small catch bottle to hang it in.
- Rags or shop towels, and a syringe or turkey baster for pulling old fluid out of the reservoir.
- The correct driver for the reservoir cap screws.
- Optional but genuinely helpful for a solo job: a one-way check-valve bleeder or a vacuum bleeder.
Setting Up Without Damaging the Bike
Get the Monkey secure and upright on a stand so it cannot tip while you are leaning on the lever. For the front circuit, turn the handlebars until the reservoir on the bar sits level — a tilted reservoir will spill the moment you open the cap. Then drape rags over the tank area, the plastics, the instrument cluster, and anything else below the reservoir. Brake fluid attacks paint and plastic on contact, and a drip you do not notice can leave a permanent mark. If a spill does happen, wipe it up immediately and rinse the area with water rather than waiting until the job is finished.
The Bleeding Procedure, Front and Rear
- Wipe the reservoir cap and surrounding area clean so no grit falls in, then remove the cap and diaphragm.
- Use the syringe or baster to draw most of the old fluid out of the reservoir. Leave a little in the bottom — do not let the reservoir run dry, or you will pull air straight into the master cylinder.
- Top the reservoir up with fresh fluid from the sealed container.
- Push the clear tubing onto the bleeder valve and route the other end into the catch bottle, making sure the tube runs upward or at least does not loop down and trap air.
- Fit the box-end wrench onto the bleeder.
- Squeeze the front lever and hold it firm. Keep it held.
- Open the bleeder about a quarter turn. Fluid and any trapped air will push out through the tube. Watch the tube, not the wrench.
- Close the bleeder fully before you release the lever. Releasing with the bleeder open sucks air back in through the valve.
- Repeat the squeeze–hold–open–close–release cycle, checking the reservoir level every few pumps and topping it off so it never drops low enough to draw air.
- Keep going until the fluid coming through the tube is clean and free of bubbles, and the lever feels firm rather than spongy.
- Move to the rear circuit and repeat the same sequence using the foot pedal instead of the lever. If your bike has more than one front caliper, bleed each caliper individually, starting with the one farthest from the master cylinder and working toward the closest.
Sealing Up and Checking Your Work
When the fluid runs clean at both ends, tighten each bleeder snugly. Snug is the goal — do not lean on it, because overtightening can damage the seat and create a leak where there was none. Fill the reservoir to the 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 the master cylinder and caliper for any weeping or wetness. A dry fitting after a few minutes of sitting is what you want to see.
Testing Before You Ride Normally
With the bike still on the stand, squeeze the lever and press the pedal. Both should feel firm and consistent, and neither should slowly sink while you hold steady pressure. Spin each wheel by hand to confirm the brakes are not dragging — a wheel that stops quickly on its own means something is still binding. Then take the bike to a quiet, safe area and test the brakes at low speed before riding normally. If anything feels vague at that first gentle stop, go back and bleed again rather than riding it out.
When to Hand the Job to a Shop
Some problems are a signal to stop. If the lever will not firm up after several honest bleeding attempts, if it only firms up after pumping, if bubbles keep appearing no matter how long you bleed, or if you find fluid leaking from the master cylinder or a caliper, the system needs a professional look. The same goes for any situation where air may have entered the ABS unit, and for any bike with a linked or combined braking system, which has additional bleed points and a required sequence that is easy to get wrong. On a safety-critical system, knowing when to stop is part of the skill.
Related Shopping Categories
Shop Brake Fluid for a 2021 Honda Monkey Motorcycle.
Shop Brake Lines for a 2021 Honda Monkey Motorcycle.
Shop Brake Pads for a 2021 Honda Monkey Motorcycle.
Shop Stands for a 2021 Honda Monkey Motorcycle.
Shop Brake Tools for a 2021 Honda Monkey 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.
