How To Bleed 1979 Honda CB650 Motorcycle Brakes

Bleeding the Front Hydraulic Brake on a 1979 Honda CB650

The 1979 Honda CB650 uses a hydraulic disc brake at the front and a mechanical drum brake at the rear. That layout matters before you pick up a wrench: the front brake is the hydraulic circuit on this bike that uses fluid, so it is the brake you bleed. The rear drum is operated by cable or rod and is adjusted, not bled. This CB650 also predates ABS and linked brake systems, so the job is a conventional manual bleed of the front master cylinder, line, and caliper. If your particular bike has been modified with a second front caliper, the same procedure applies to each caliper in turn.

Why and When the CB650 Front Brake Needs Bleeding

A brake bleed does two jobs at once: it pushes old fluid out of the system and removes air that has found its way in. On a CB650 of this age, the most common complaint is a lever that feels soft or spongy, or one that pulls closer to the grip than it used to. Dark, cloudy, or contaminated fluid in the reservoir is another sign that a flush is overdue. You should also bleed the front brake after any work that opened the hydraulic system, such as replacing a brake line, servicing the caliper, or repairing the master cylinder.

Even when the lever still feels acceptable, brake fluid absorbs moisture from the air over time. Moisture lowers the fluid’s boiling point, which can lead to brake fade under hard or repeated use. Many riders refresh the fluid on a regular schedule as preventive maintenance rather than waiting for a problem to appear. If you are unsure when the fluid was last changed, a bleed is a sensible starting point.

Tools and Supplies to Gather

• Fresh brake fluid of the type marked on the master cylinder reservoir cap, from a sealed container
• A box-end wrench that fits the caliper bleeder valve
• A length of clear tubing that fits snugly over the bleeder
• A small catch bottle for the old fluid
• Rags or shop towels, plus a syringe or turkey baster for removing old fluid from the reservoir
• A screwdriver that fits the reservoir cap screws
• Optional: a one-way check-valve bleeder or a vacuum bleeder, which can make the job easier for one person

Keep the fluid container capped when you are not pouring from it, and do not reuse fluid that has been sitting open. Fresh fluid from a sealed container is the only fluid that belongs in this front brake system.

Preparing the Bike and Protecting the Finish

Support the CB650 securely upright on a stand so it cannot tip while you are working at the handlebar. Turn the handlebars until the front reservoir sits level; if the reservoir is tilted, you cannot judge the fluid level accurately and it is easier to spill. Before opening the cap, cover the painted surfaces, plastics, and instrument area with rags. Most brake fluids damage paint and plastic on contact, so treat every drip as something to wipe up immediately. If a spill does happen, wipe it promptly and rinse the area with water.

Once the area is protected, remove the reservoir cap and diaphragm. Set them on a clean rag where they will not pick up grit. Do not leave the reservoir open for long periods, and do not begin the bleed until you have everything staged within reach.

Bleeding the Front Brake: Step by Step

1. Use the syringe or turkey baster to remove most of the old fluid from the reservoir. Leave enough fluid in the bottom that you do not expose the master cylinder inlet to air.
2. Refill the reservoir with fresh fluid of the type marked on the cap. Keep the container capped between pours.
3. Fit the clear tubing over the caliper bleeder valve and route the other end into the catch bottle. The tubing should fit snugly so air cannot be drawn in around it.
4. Place the box-end wrench on the bleeder valve. You will use it to open and close the bleeder during each cycle.
5. Squeeze the front brake lever and hold it firmly. Do not release it yet.
6. Open the bleeder about a quarter turn. Fluid and any trapped air will travel down the clear tube. Watch the tube, not the reservoir, during this moment.
7. Close the bleeder before you release the lever. This order is critical: if you release the lever while the bleeder is open, air can be drawn back into the caliper.
8. Release the lever slowly, then repeat the squeeze-hold-open-close-release cycle. Check the reservoir after every few cycles and top it off so it never runs low enough to draw air into the master cylinder.
9. Continue until the fluid coming through the clear tube is fresh, clean, and free of bubbles. On a single-caliper front brake, there is only one caliper to bleed. If your bike has been fitted with a second front caliper, start with the caliper farthest from the master cylinder and then bleed the other one.
10. When the fluid runs clear and bubble-free, close the bleeder and remove the tubing. Keep the reservoir topped off to the correct level marking.

Finishing Up and Checking Your Work

Tighten the bleeder snugly with the box-end wrench, but do not overtighten it. Reinstall the reservoir diaphragm and cap, making sure the diaphragm sits flat and the cap seals properly. Wipe down the caliper, bleeder, and reservoir area with a clean rag, and rinse away any fluid that reached painted or plastic surfaces. Check for leaks at the bleeder valve and at the banjo fittings on the brake line. A dry fitting after several lever pulls is what you want to see.

Testing the Brake Before Normal Riding

With the bike still supported, pull the front lever several times. It should feel firm and consistent, not spongy, and it should not slowly sink toward the grip while you hold steady pressure. Spin the front wheel and confirm the brake is not dragging; a slight pad rub is normal, but the wheel should turn freely enough that you can feel the difference between normal drag and a brake that is staying applied. Before riding normally, test the brake at low speed in a safe area such as an empty lot. Apply it gently, then more firmly, and confirm it slows the bike smoothly and releases cleanly.

Troubleshooting a Lever That Will Not Firm Up

If the lever still feels soft after several bleeding cycles, do not keep riding and hoping it improves. A lever that firms up only after pumping usually means air is still trapped somewhere in the system. Persistent bubbles at the bleeder can point to a loose tube fit, a bleeder that is not sealing, or air being drawn in during the release stroke. Fluid leaking from the master cylinder or caliper is a separate problem that needs attention before the bike is ridden. Because this CB650 has no ABS or linked brake hardware, there is no module to worry about, but a lever that will not firm up after repeated attempts is still a sign to stop and have a shop inspect the system. The same applies if you see fluid weeping from a fitting or if the lever behavior changes unpredictably.

Related Shopping Categories

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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.