Bleeding the Brakes on a 1991 Honda ST1100
Shop parts for a 1991 Honda ST1100 Motorcycle.
Know What You Are Working On
The 1991 Honda ST1100 is a fully hydraulic motorcycle: disc brakes at the front wheel and a disc brake at the rear, each with its own master cylinder, reservoir, and caliper. There is no mechanical drum brake anywhere on this machine, so both ends of the bike are bled the same way—by pushing fresh fluid through the system and driving trapped air out ahead of it. This particular model year predates the era of anti-lock and linked braking on this platform, so you are dealing with two independent, conventional hydraulic circuits. That is good news for a home mechanic, because each circuit can be serviced on its own without any special sequence or electronic tool.
If your bike has two front calipers, treat them as two separate bleed points fed by the same master cylinder, and bleed each one in turn. The rear circuit is entirely separate and gets its own session with the pedal.
Why and When to Bleed
Brake fluid is hygroscopic, meaning it pulls moisture out of the air over time. Moisture does two harmful things: it lowers the fluid's boiling point, so hard, repeated braking can boil the fluid and produce a soft, fading lever, and it corrodes the internals of the master cylinder and calipers. That is why many riders refresh the fluid on a routine interval even when the brakes still feel fine.
Bleed immediately if the lever or pedal feels spongy, if the lever now travels closer to the grip than it used to, if the fluid in the reservoir looks dark or cloudy, or if you have just opened the hydraulic system—new lines, caliper service, or master cylinder work all introduce air that must be purged. A lever that firms up only after several quick pumps is a classic sign of air in the lines.
Tools and Supplies
- Fresh brake fluid of the type marked on the master cylinder reservoir cap, from a sealed container. Do not substitute a different type.
- A box-end wrench that fits the bleeder valve snugly—the box end grips the flats far better than an open end and is less likely to round them off.
- A length of clear tubing that fits tightly over the bleeder nipple, plus a 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 helpful: a one-way check-valve bleeder or a vacuum bleeder, either of which makes a one-person job much easier.
Setting Up Before You Open Anything
Get the bike 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 handlebar sits level; a tilted reservoir will spill fluid the moment the cap comes off. Drape rags over the bodywork, the instrument area, and any painted surface below the reservoir, because brake fluid attacks paint and plastic almost on contact. If a drop lands where it should not, wipe it up immediately and rinse the area with water.
Work through one circuit at a time. Finish and button up the front before you move to the rear, so you never have two reservoirs open at once.
The Bleeding Procedure, Step by Step
- Clean the reservoir cap and the area around it so grit cannot fall in, then remove the cap and the diaphragm.
- Use the syringe or baster to draw most of the old fluid out of the reservoir. Leave enough at the bottom that you are not pulling air into the master cylinder port.
- 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, with the bottle positioned so the tube's end stays submerged.
- Fit the box-end wrench onto the bleeder. If your bike has two front calipers, start with the caliper farthest from the master cylinder in terms of hydraulic path, then do the other.
- Squeeze the lever slowly and hold it against the grip. Do not stab at it—slow, full strokes move fluid without aerating it.
- With the lever held, open the bleeder about a quarter turn. Fluid and air will push out through the tube. Watch the tube, not the reservoir.
- Close the bleeder before you release the lever. Releasing with the bleeder open draws air straight back into the caliper, which is the single most common way this job goes wrong.
- Release the lever, then check the reservoir and top it off. Repeat the squeeze–hold–open–close–release cycle until the fluid coming through the tube is clean and free of bubbles.
- Keep topping the reservoir off throughout. If it ever runs low enough to draw air at the bottom, you have to start over on that circuit.
- Move to the rear circuit and repeat the same cycle using the brake pedal, holding it down while the bleeder is open and closing the bleeder before letting it up.
Finishing the Job
When the fluid runs clean at every bleed point, close the bleeder snugly. Snug is the goal—do not lean on it, because overtightening can damage the seat and cause a leak. Fill the reservoir to the level marking, reinstall the diaphragm and cap, and wipe down every surface you touched. Then inspect the bleeder and the banjo fittings at the caliper and master cylinder for weeping fluid; a dry paper towel wiped around each joint will tell you quickly.
Testing Before You Ride
Pull 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. Then, in a safe, empty area, test the brakes at low speed before riding normally. If anything feels soft or inconsistent, stop and diagnose rather than riding it out.
When to Stop and See a Shop
If the lever will not firm up after several full bleeding cycles, if it firms only after pumping, if bubbles keep appearing no matter how long you bleed, or if fluid is leaking from the master cylinder or a caliper, the problem is beyond a simple flush and the bike should go to a professional. The same applies if the reservoir has run dry and you suspect air has traveled deeper into the system than the bleeders can reach. A brake system that will not hold pressure is not something to test on the road.
Related Shopping Categories
Shop Brake Fluid for a 1991 Honda ST1100 Motorcycle.
Shop Brake Lines for a 1991 Honda ST1100 Motorcycle.
Shop Brake Pads for a 1991 Honda ST1100 Motorcycle.
Shop Stands for a 1991 Honda ST1100 Motorcycle.
Shop Brake Tools for a 1991 Honda ST1100 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.
