How To Bleed 1979 Honda CB400T2 - Hawk II Motorcycle Brakes

Bleeding the Front Brake on a 1979 Honda CB400T2 Hawk II

The 1979 Honda CB400T2 Hawk II uses a hydraulic disc brake at the front and a mechanical drum brake at the rear. That distinction matters before you start: this article covers bleeding the front hydraulic brake only. The rear drum brake does not use brake fluid and is adjusted through its mechanical linkage rather than bled. This model also predates ABS and linked brake systems, so the front circuit is a straightforward hydraulic system with a master cylinder, line, and caliper.

Why and When the CB400T2 Front Brake Needs Bleeding

Bleeding serves two purposes on the CB400T2: it removes air from the hydraulic circuit and it replaces old fluid with fresh fluid. Air is compressible, so even a small bubble can make the front lever feel spongy, vague, or closer to the grip than it should be. Old fluid is a separate problem. Brake fluid absorbs moisture over time, which lowers its boiling point and can contribute to brake fade under hard or repeated use. Dark, cloudy, or contaminated fluid in the reservoir is a clear sign that a fluid refresh is overdue.

You should also bleed the front brake after any work that opened the hydraulic system, such as replacing the brake line, servicing the caliper, or working on the master cylinder. Many riders refresh the fluid on a regular schedule even when the lever still feels acceptable, because moisture uptake happens gradually and does not always produce an obvious symptom at first. If the lever pulls in farther than it used to, feels inconsistent, or slowly sinks under steady pressure, treat that as a reason to inspect and bleed the system before riding normally.

Tools and Supplies to Have Ready

• Fresh brake fluid of the type marked on the master cylinder reservoir cap, from a sealed container
• A box-end wrench that fits the front bleeder valve
• A length of clear tubing that fits snugly over the bleeder
• A catch bottle for the old fluid
• Rags or shop towels, plus water for rinsing spills
• 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 vacuum bleeder to make the job easier for one person

Use only fluid from a sealed container, and do not reuse fluid that has been sitting open or that was bled out of the system. Brake fluid damages paint and many plastics on contact, so keep rags close and wipe up any spill immediately. If fluid reaches a painted or plastic surface, rinse the area with water rather than wiping it deeper into the finish.

Preparing the Bike and Protecting Surfaces

Support the CB400T2 securely upright on a stand so it cannot tip while you are working at the front end. Turn the handlebars so the front master cylinder reservoir sits level; if the reservoir is tilted, it is easy to spill fluid or let the reservoir run dry at the wrong moment. Cover the painted surfaces, plastics, instrument area, and surrounding bodywork with rags or shop towels before you open the reservoir.

Clean the area around the reservoir cap before removing it so dirt does not fall into the fluid. Remove the cap and diaphragm, then inspect the fluid. If the reservoir is very low or the fluid is dark, plan on a full flush rather than a quick bleed. Keep the cap and diaphragm clean and set them aside where they will not pick up grit.

Step-by-Step Front Brake Bleeding Procedure

1. With the bike supported and the reservoir level, remove most of the old fluid from the reservoir using a syringe or turkey baster. Do not let the reservoir run completely dry; leave enough fluid to avoid pulling air into the master cylinder.
2. Refill the reservoir with fresh fluid of the type marked on the cap. Keep the container sealed when you are not pouring, and avoid shaking the bottle unnecessarily.
3. Fit the box-end wrench over the front bleeder valve. Push the clear tubing onto the bleeder so it fits snugly, and route the other end into the catch bottle. The tubing should slope upward or run cleanly to the bottle so you can see bubbles moving through it.
4. Squeeze the front brake lever slowly and hold it. With the lever held, open the bleeder about a quarter turn. Fluid and any trapped air will move out through the tubing.
5. 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.
6. Release the lever slowly, then check the reservoir level and top it off with fresh fluid. Repeat the squeeze-hold-open-close-release sequence, topping off the reservoir throughout so it never runs low enough to draw air in.
7. Continue until the fluid coming through the clear tubing is fresh, clean, and free of bubbles. Watch the tubing closely; a stream with no visible bubbles is what you are after, not just a change in color.
8. If your particular bike has more than one front caliper, bleed each caliper one at a time and begin with the caliper farthest from the master cylinder. On a single front brake, work the one caliper through the same sequence until the fluid is clean and bubble-free.
9. When you are satisfied, close the bleeder snugly. Tighten it firmly without overtightening, since the bleeder is small and easy to damage if you force it.

Finishing the Bleed and Checking for Leaks

Fill the reservoir to the correct level marking, then reinstall the diaphragm and cap. Wipe any fluid residue from the reservoir, caliper, bleeder, and surrounding surfaces, and rinse with water if fluid reached paint or plastic. Check for leaks at the bleeder valve and at the banjo fittings on the master cylinder and caliper. A dry fitting after several lever pulls is a good sign; a wet fitting or a drip means you need to stop and correct it before testing the brake.

Look over the brake line as well. A line that is cracked, swollen, or wet at a fitting should be addressed before the bike is ridden. Bleeding cannot fix a line that is letting air in or fluid out.

Testing the CB400T2 Brake Before Riding

Pull the front lever firmly 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 wheel that stops quickly or feels tight may indicate an overfilled system, a misadjusted caliper, or a problem that needs attention. Test the brake at low speed in a safe area before riding normally, and make sure the lever feel remains consistent after the bike is moving.

Troubleshooting and When to Stop

If the lever will not firm up after several careful bleeding rounds, or if it firms up only after pumping, air is still entering or remaining in the system. Persistent bubbles at the bleeder, fluid leaking from the master cylinder or caliper, or a lever that feels different from one pull to the next are all reasons to stop and diagnose rather than keep riding. This bike has no ABS unit to trap air, but a stubborn hydraulic problem still deserves a professional inspection. If you are unsure whether the system is holding pressure safely, have a shop pressure-bleed or inspect the front brake before you ride.

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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.