How to Bleed the Front Brake on a 1978 Kawasaki KH400
Shop parts for a 1978 Kawasaki KH400 Motorcycle.
Know Which Brake You Are Servicing
The 1978 Kawasaki KH400 uses a hydraulic disc brake at the front and a mechanical drum brake at the rear. That distinction matters before you pick up a wrench. The front system has a master cylinder at the handlebar, a hydraulic line, and a caliper at the wheel; bleeding removes air and old fluid from that closed circuit. The rear drum is operated by cable or rod and does not contain brake fluid, so it is adjusted rather than bled. This article covers the front hydraulic brake only. The KH400 predates ABS and linked braking, so there is no ABS unit or combined-brake sequence to worry about. If your particular bike has been modified with different brake hardware, use the hardware in front of you as your guide and stop if anything does not match.
When a Bleed Is Due
A soft or spongy lever, a lever that travels closer to the grip than it used to, or a lever that feels firm only after several quick pumps are classic signs of air in the front system. Dark, cloudy, or contaminated fluid in the reservoir is another reason to flush. Bleeding is also required after work that opens the hydraulic circuit: new brake lines, caliper service, master cylinder work, or any time the reservoir has run low enough to pull air into the line. Even without symptoms, brake fluid absorbs moisture over time. Moisture lowers the fluid’s boiling point, which can cause fade under hard or repeated braking. Many riders refresh the fluid on a regular schedule as preventive maintenance.
Tools and Supplies to Gather
- Fresh brake fluid of the type printed on the master cylinder reservoir cap, from a sealed container
- A box-end wrench that fits the bleeder valve on the front caliper
- Clear tubing that fits snugly over the bleeder valve
- A small catch bottle for used fluid
- Rags or shop towels, plus water for rinsing spills
- A syringe or turkey baster for removing old fluid from the reservoir
- The correct screwdriver or driver for the reservoir cap screws
- Optional: a one-way check-valve bleeder or vacuum bleeder to make one-person bleeding easier
Brake fluid damages paint and many plastics on contact, so keep rags handy and wipe up any spill immediately. Rinse the area with water if fluid reaches painted or plastic surfaces.
Set Up the Bike and Protect the Finish
Support the KH400 securely upright on a stand so it cannot tip while you work at the handlebar. Turn the handlebars until the front master cylinder reservoir sits level; if the reservoir is tilted, you cannot judge the fluid level correctly and it is easier to spill. Cover the instrument area, the top of the bodywork, and any painted surfaces below the reservoir with rags. Remove the reservoir cap and diaphragm according to the cap screws or retaining hardware on your bike, and set them on a clean towel where they will not pick up grit.
Bleeding the Front Brake Step by Step
- Use the syringe or turkey baster to remove most of the old fluid from the reservoir. Leave enough fluid in the bottom so you do not push air into the master cylinder, but remove the dark or cloudy fluid you can see.
- Refill the reservoir with fresh fluid from the sealed container, up to the level marking. Keep the container capped when you are not pouring.
- Fit the clear tubing over the caliper bleeder valve and route the other end into the catch bottle. The tube should fit snugly so air cannot be drawn in around it.
- Place the box-end wrench on the bleeder valve. Squeeze the front brake lever and hold it firmly against the grip.
- With the lever held, open the bleeder valve about a quarter turn. Fluid and air will move through the tube. Close the bleeder valve before you release the lever. Do not release the lever while the bleeder is open, or air can be drawn back into the caliper.
- Release the lever slowly, then repeat the squeeze-hold-open-close-release sequence. Check the reservoir level often and top it off before it gets low. The reservoir must never run dry during bleeding.
- Continue until the fluid coming through the clear tube is fresh, clean, and free of bubbles. Tiny bubbles may take several cycles to clear.
- If a front end has more than one caliper, bleed each caliper in turn. As a general practice, start with the caliper farthest from the master cylinder, then move to the closer caliper, topping off the reservoir between calipers.
Finish the Job and Check for Leaks
When the fluid runs clear and bubble-free, close the bleeder valve snugly with the box-end wrench. Tighten it firmly enough to seal, but do not overtighten it; the bleeder is small and can be damaged by excess force. Fill the reservoir to the correct level marking with fresh fluid. Reinstall the diaphragm and cap, making sure the diaphragm is seated properly and not pinched. Wipe down the caliper, bleeder, line fittings, and reservoir area with a clean rag, then rinse away any fluid that reached paint or plastic. Inspect the bleeder valve and the banjo fittings at the master cylinder and caliper for weeping or wetness.
Test Before You Ride
Squeeze the front lever firmly and hold it under steady pressure. It should feel firm and consistent, not spongy, and it should not slowly sink toward the grip. Spin the front wheel and confirm the brake is not dragging; a slight pad rub is normal on some bikes, but the wheel should still turn freely. Test the brake at low speed in a safe, open area before riding normally. Confirm the lever feel stays consistent. If the lever changes or the brake feels weak, stop and investigate before going faster.
When to Stop and See a Shop
If the lever will not firm up after several careful bleeding cycles, or if it firms only after pumping, air is still trapped somewhere or fluid is bypassing internally. Persistent bubbles, fluid leaking from the master cylinder or caliper, or a lever that slowly sinks under steady pressure are reasons to stop. Because this KH400 has a simple front hydraulic circuit, most front-brake bleeds are within reach of a careful home mechanic, but a problem that does not respond to normal bleeding is not something to ride out. Have the system inspected before the bike goes back on the road.
Related Shopping Categories
Shop Brake Fluid for a 1978 Kawasaki KH400 Motorcycle.
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Shop Brake Pads for a 1978 Kawasaki KH400 Motorcycle.
Shop Stands for a 1978 Kawasaki KH400 Motorcycle.
Shop Brake Tools for a 1978 Kawasaki KH400 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.
