Bleeding the Brakes on a 1979 Honda CBX

Shop parts for a 1979 Honda CBX Motorcycle.

The six-cylinder engine is what people talk about, but the brake system on a 1979 Honda CBX deserves just as much of your attention. This machine uses hydraulic disc brakes at both ends: a handlebar-mounted master cylinder feeding the front caliper or calipers, and a pedal-actuated master cylinder feeding the rear caliper. There is no ABS controller and no linked-brake plumbing on this bike, which is good news for a home mechanic — each hydraulic circuit stands alone, and bleeding one has no effect on the other. That means you can service the front and rear systems separately, on your own schedule, with ordinary hand tools.

Know What You Are Working On

Before you touch anything, walk around the bike and identify the parts you will be dealing with. Up front, the master cylinder sits on the handlebar with a small reservoir capped by a cover held with screws. Follow the line down to the caliper at the fork leg. If your bike carries two front calipers, treat them as two separate bleed points and do them one at a time rather than trying to open both at once. At the rear, the master cylinder is actuated by the brake pedal, and the caliper is mounted at the rear wheel with its own bleeder fitting. Each caliper has a bleeder valve — a small hex fitting with a rubber cap over the tip. Locate every one of them now, before your hands are oily, so you are not hunting for a bleeder halfway through the job.

Signs That the System Needs Fresh Fluid

Brake fluid is hygroscopic, meaning it pulls moisture out of the air over time. On a bike as old as the CBX, that process has had decades to work, and even a well-kept example will benefit from periodic flushing. Moisture lowers the fluid's boiling point, so under hard or repeated braking the fluid can boil and create vapor in the lines — which feels exactly like air and gives you a lever that goes soft just when you need it most. Watch for a lever or pedal that feels spongy, a lever that now comes noticeably closer to the grip than it used to, fluid in the reservoir that looks dark, cloudy, or gritty, and any recent work that opened the hydraulic system, such as new lines, a caliper rebuild, or master cylinder service. Many riders simply refresh the fluid on a regular interval as preventive maintenance, and on a CBX that habit is well worth keeping.

Tools and Supplies to Collect

  • Fresh brake fluid of the type marked on the master cylinder reservoir cap, from a sealed container — once a container has been opened and sitting, moisture gets in, so start fresh
  • A box-end wrench that fits the bleeder valve snugly
  • A length of clear tubing that fits tightly over the bleeder nipple
  • A small catch bottle for the old fluid
  • Rags or shop towels, plus a syringe or turkey baster for pulling old fluid out of the reservoir
  • The correct driver for the reservoir cover screws
  • Optional: a one-way check-valve bleeder or a vacuum bleeder, both of which make a solo job much less fiddly

Setting Up Without Damaging the Bike

Get the CBX upright and stable on a stand so it cannot tip while you are working. For the front circuit, turn the handlebars until the reservoir sits level — an angled reservoir will spill as soon as you open it. Then drape rags over the tank, the fairing or side panels, the instruments, and anything else below the reservoir. Brake fluid attacks paint and many plastics on contact, and a single drip can leave a permanent mark. If a spill does happen, wipe it up immediately and rinse the area with water rather than letting it sit.

The Bleeding Procedure

  1. Open the reservoir cover and lift out the diaphragm. Use the syringe or baster to draw most of the old fluid out of the reservoir, leaving the bottom covered so you do not push air into the line.
  2. Top the reservoir up with fresh fluid from your sealed container.
  3. Push the clear tubing onto the bleeder nipple and route the other end into the catch bottle, with the bottle positioned so the tube end stays submerged.
  4. Squeeze the front lever, or press the rear pedal, and hold it steady under pressure.
  5. Open the bleeder about a quarter turn. Fluid and any trapped air will push out through the tube. Watch the tube, not your hands.
  6. Close the bleeder before you release the lever or pedal. Releasing first will suck air back in through the open valve.
  7. Release the lever or pedal slowly and let it return fully.
  8. Check the reservoir and top it off. Never let the level drop far enough to uncover the port — that is how air enters the system and turns a ten-minute job into an afternoon.
  9. Repeat the squeeze-hold-open-close-release cycle until the fluid coming through the tube runs clean and free of bubbles.
  10. If your bike has two front calipers, repeat the whole sequence on the second caliper. As a general practice, start with the caliper farthest from the master cylinder and work toward the closest one.
  11. When you move to the rear circuit, follow the same steps with the pedal, using its own reservoir and bleeder.

Finishing the Job Cleanly

Once clean fluid is flowing, close the bleeder snugly with your box-end wrench. Snug is the goal — do not lean on it, because overtightening can damage the valve seat. Refill the reservoir to the level marking on the body, reinstall the diaphragm and cover, and wipe down every surface you touched. Then inspect the bleeder fittings and the banjo bolts at the caliper and master cylinder for weeping or dampness. A dry fitting after a few firm lever pulls is what you want to see.

Confirming the Brakes Are Right

The lever and pedal should feel firm and consistent, and should hold pressure without slowly sinking while you keep a steady squeeze on them. Spin each wheel by hand to make sure the brake is not dragging. Then, in a safe open area, test the brakes at low speed before riding normally. If anything feels vague, stop and investigate rather than riding it out.

When to Stop and Call a Shop

If the lever will not firm up after several rounds of bleeding, if it only firms up after pumping, if bubbles keep appearing no matter how long you work, or if you find fluid leaking from the master cylinder or a caliper, put the tools down and have the system inspected professionally. The same applies if you are simply not confident in what you are seeing. Brakes are not the place to guess, and a professional diagnosis is far cheaper than a failed lever on the road.

Related Shopping Categories

Shop Brake Fluid for a 1979 Honda CBX Motorcycle.

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Shop Brake Pads for a 1979 Honda CBX Motorcycle.

Shop Stands for a 1979 Honda CBX Motorcycle.

Shop Brake Tools for a 1979 Honda CBX 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.