HAYES DISC BRAKE TUNING

Centering Calipers Over Rotors

Bleeding Hayes Disc Brakes

Hayes disc brakes are among the simplest to tune and most reliable disc brakes made for bicycles. Once a system has been assembled and installed, getting them to operate completely drag-free is a simple 3-step process.

1. Firstly, you must reset the caliper's pistons into their fully retracted state. This may be done either with the caliper mounted to the frame (or fork) or not. With the pads installed and using a large, broad flat-head screwdriver, gently pry apart the pads unit they are fully open. Be careful not to chip or score the pad's surfaces by applying too much force.

2. Secondly, you must set the pad-to-rotor spacing. If the caliper is not already mounted on the frame or fork, it must be remounted. THE NEXT INSTRUCTION IS VERY IMPORTANT. The mounting screws of the caliper should be left loose enough to let the caliper float freely from side to side but not so loose that it can rock easily and lift the away from the mounting surface(s). With the wheel and rotor installed, place one 0.015" feeler gauge between each pad and the rotor (business cards work very well) and squeeze the lever firmly a few times to set the pad-to-rotor spacing. Having the caliper free to float while performing this step, prevents a non-centered caliper from flexing the rotor and potentially causing permanent warpage.

3. Thirdly and lastly, the caliper must be centered over the rotor. Remove the spacers (the caliper's bolts should still be loose) and press the lever a couple of times. Now hold the lever down and tighten the bolts. Tighten each bolt a small amount at a time and alternate between bolts until they are tight enough. Doing this will help to prevent the caliper from shifting from it's centered position during the tightening of the bolts. It is possible to set Hayes brakes up so that they run totally free of drag.

Sometimes the third step is not enough to eliminate all the drag. The reasons for this could be that the rotor has a very slight warp to it, or that the caliper's pistons are not functioning symmetrically causing one of the pads to contact the rotor occasionally or constantly. In these situations, you can retry step 3 while placing a spacer (0.015" feeler gauge or business card) between only the delinquent pad and the rotor. Another possible reason for drag is that the caliper was shifted as the bolts were tightened due to the rotation of the bolts themselves. The remedy for this is to apply rotational pressure to the wheel so that the brake caliper is forced to lay flat on the mounting surface as you squeeze the lever and tighten the bolts (unless you are an octopus, you will need a helper for this procedure). Remember to alternate between bolts as you tighten them. Employing these techniques will result in totally drag free operation of your Hayes disc brakes.


Bleeding a Hayes Disc Brake System  

Centering Caliper Over Rotor

You will need a Hayes bleed kit to bleed a Hayes disc brake. If you are a handy man you can make a bleeding bottle yourself.

Use only DOT3 or DOT4 brake fluid. DOT3 and DOT4 brake fluid will strip paint, so wipe up spilled fluid immediately. Clean all brake parts with  alcohol after bleeding or fluid replacement. Using brake cleaner or other cleaning agents will contaminate the brake pads, rendering them useless.

Before bleeding any disc brake, it is advisable to remove the pads in order to avoid contaminating them with brake fluid. Hayes disc brakes are best bled when the system is arranged such that the master cylinder bleeder screw (on the lever) is the highest point on the system and the caliper is the lowest, with the caliper's bleeder screw oriented vertically and pointing up. Position the bike so that the hose end of the lever is pointing down at 45°. Naturally, the rest of the hose should be oriented as vertically as possible with no dips where air can collect.

1. Remove the master cylinder bleed screw and insert the bleed fitting with hose (from bleed kit) into the screw hole. Run the other end of the bleed hose into a small container to catch the overflow.

2. Remove the rubber cap from the caliper's bleeder nipple and engage the bleeder nipple with a six-point, 8mm box wrench. Now fit the fluid bottle's hose (from bleed kit) over the bleed nipple keeping the bottle inverted. This system works best when the fluid bottle's hose is no more than 2cm long.

3. Open the bleed nipple with the box wrench and firmly squeeze the fluid bottle for a count of 5 and the release for a count of 3. This action forces fluid into the system and when the bottle is relaxed, air is drawn out of the caliper. Continue this procedure until no more air comes out of the caliper. You may want to tap or wiggle the caliper to shake loose any air bubbles that are stuck on the inside walls of the caliper.

4. The caliper should now be filled with no air trapped inside. Firmly squeeze the fluid bottle until fluid comes out of the master cylinder free of air bubbles. While still squeezing the bottle, close the caliper's bleed nipple. This prevents air from being drawn in from the master cylinder's bleed port.

5. Remove the bleed hose from the master cylinder and reinstall the bleed screw.

6. CLEAN THE CALIPER, LEVER, AND ROTORS WITH  ALCOHOL (CAN BE BOUGHT AT ANY PHARMACY) TO AVOID STRIPPING PAINT AND PERMANENTLY CONTAMINATING THE BRAKE PADS.