Bleeding the Front Brake on a 1991 Yamaha YSR50
Shop parts for a 1991 Yamaha YSR50 Motorcycle.The 1991 Yamaha YSR50 is a mini sportbike with a hydraulic disc brake up front and a mechanical drum at the rear. The front disc is fed by a small master cylinder and reservoir on the right handlebar and is the only part of the brake system that uses fluid. Bleeding this bike is a front-only job; the rear drum is adjusted, not bled.
Why the Front Brake Needs Fresh Fluid
Brake fluid absorbs moisture over time, lowering its boiling point and causing internal corrosion. On a small bike that may have been parked for years, the fluid can turn dark or sludgy and the caliper piston may start to stick. Fresh fluid restores a firm lever and protects parts that can be hard to find.
- The lever feels spongy or pulls close to the grip
- The reservoir fluid is dark, cloudy, or has sediment
- The bike has been in storage
- The caliper, hose, or master cylinder was recently serviced
Tools and Supplies
- Fresh brake fluid of the type marked on the master cylinder reservoir cap, from a sealed container
- A box-end wrench that fits the bleeder valve
- Clear tubing that fits snugly over the bleeder
- A catch bottle
- A small syringe
- A screwdriver for the reservoir cap
- Penetrating oil and rags
Preparing the Bike
Support the bike securely upright so it can’t tip. Turn the handlebars until the reservoir is level. Cover the bodywork and tank with rags, because brake fluid damages paint and plastic. Wipe spills immediately and rinse with water. Clean around the reservoir cap before opening, and treat a corroded bleeder with penetrating oil ahead of time.
Bleeding the Front Brake
- Remove the reservoir cap and diaphragm.
- Draw out most of the old fluid with the syringe without letting the reservoir run dry.
- Wipe out any sediment, then refill with fresh fluid.
- Attach the clear tube to the caliper bleeder and place the free end in the catch bottle.
- Squeeze and hold the lever.
- Open the bleeder about a quarter turn.
- Close the bleeder before releasing the lever.
- Repeat, topping off the small reservoir every couple of strokes so it never draws in air.
- Continue until clean, bubble-free fluid flows through the tube.
- Close the bleeder snugly.
About the Rear Drum Brake
The rear brake is a mechanical drum operated from the foot pedal. It has no fluid and nothing to bleed. Check the rear adjustment and wear indicator while you’re working, and make sure the brake releases fully.
Tips for Small Brake Systems
- The reservoir is small, so it empties quickly; check it constantly.
- Use a box-end wrench on the small bleeder to avoid rounding it.
- Inspect the brake hose for cracks or swelling.
- Never reuse fluid from the catch bottle.
Finishing and Testing
Fill the reservoir to the correct level, reinstall the diaphragm and cap, and clean up all spilled fluid. Check the bleeder and fittings for leaks, and dispose of the old fluid properly. The lever should feel firm and should not slowly sink under steady pressure. Spin the front wheel to make sure the brake isn’t dragging, then test both brakes at low speed in a safe area before riding normally.
When to Get Help
If the lever won’t firm up, only firms after pumping, or the caliper or master cylinder leaks, the internal seals may be worn out. A rebuild or replacement may be needed, and a shop can help.
Related Shopping Categories
Shop Brake Fluid for a 1991 Yamaha YSR50 Motorcycle.
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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.
