Hayes® Hydraulic Brake Service
This article will discuss the service and adjustment of Hayes® hydraulic disc brake systems. For information on the disc rotor mounting and service, see Disc Rotor Installation and Truing.
If the bicycle frame or fork has the International Standard caliper mounts, use the Hayes mounting bracket. Secure the bracket to the frame mounts and tighten bolts to 110 inch-pounds (12.43 Nm). If the bike uses the “post mount” system, secure the caliper directly to the bike.
Caliper Installation & Adjustment
Loosen the caliper adjusting bolts and install the wheel and rotor. Leave the caliper bolts loose, and squeeze the brake lever. It can be useful to use a strong rubber band to hold lever closed. View the gap in the caliper body for the brake pads. Move caliper body side to side until this gap appears centered to the rotor. Tighten both mounting bracket bolts.
Spin wheel and check for brake rub. If there is rub on the rotor, adjust the caliper as necessary. It can be useful to use a white piece of paper behind the caliper to help sight close tolerances.
The Hayes hydraulic brakes use only DOT 3 or DOT 4 brake fluid. Never use a mineral oil for this system.
Begin by rotating the bike and brake levers as necessary so there is an upward flow from the caliper to the lever bleed screw.
Inspect the lever for the bleed screw. Loosen and rotate lever if necessary until screw point upward. The bleed screw of the El Camino model lever faces upward and is the highest point in the system. It is not necessary not to rotate the El Camino lever.
Remove bleed screw from brake lever and insert bleed hose fitting. Route bleed hose into bottle to catch fluid. Use rags around lever to prevent fluid from getting on frame or other components. DOT brake fluid tends to be harmful to painted surfaces and your skin.
Remove brake pads from caliper body. Grab post a end of caliper, push it way from body, and pull pad from body.
After pads are removed, push each cylinder into the caliper body. NOTE: Use care not to break post in the center of each piston. Use a box end wrench and push the cylinder into the body.
Locate bleed nipple on caliper body. Remove rubber cover from caliper. Attach tubing to end of bleed bottle. Fill bleed bottle with fluid. Attach tubing to bleed nipple. NOTE: It can be helpful to use a small zip tie to hold the tubing to the nipple.
Loosen bleed nipple 1/4 turn. Squeeze bottle firmly for approximately five seconds to force fluid into caliper. Relax bottle to draw any air out of the caliper. Continue to alternate between squeezing bottle for five seconds and releasing bottle until no air bubbles come out of caliper.
When no more air bubble appear in the bottle hose, continue to squeeze the bottle and inspect the exit hose at the lever. Squeeze until the fluid appears clear with no bubbles. Close bleed nipple.
Install and secure the lever bleed screw. Clean all parts with a rag and isopropyl alcohol. Install brake pads into caliper body. Install wheel and rotor and test lever. The lever will feel loose for a few pumps until pistons move to rotor. Lever should feel firm when pulled with force. Inspect all fittings for leaks.