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This is due to a number of factors. First, all of the pistons in a Harley Davidson caliper are virtually the same size. The further the piston is away from the source of hydraulic pressure the more pressure it requires to move at the same rate as the pistons that are closer to the source. The only way that this can be accomplished where both pistons front and rear move at the same rate is with differential bore, meaning that the pistons furthest away from the source are smaller in diameter so that less hydraulic pressure is required to move as freely as the pistons that are nearest to the source of hydraulic pressure.

The other problem that causes pistons to drag and hang-up is that since there are no dust boots on the pistons, brake dust and general road dirt accumulates around the pistons. Once the brake cleaner spray has successfully removed all of the debris, take your flat headed screw driver and place the blade in between the old pads and force the pistons back into the caliper. Have you assistant pull on the brake lever once again and repeat the process as described above until all four pistons move relatively freely.

Once you are satisfied in their performance, remove the two pins that secure the pads in place with the one inch twelve point socket. Once the pins have been removed, gently remove the pads that were secured within the caliper. Take notice of how the pads were installed since they are different in configuration. Install the two new pads. Once in place, re-insert the two pieces and loosely tighten until the caliper has been re-installed on the rotor.

Gently spread the two pads apart with your fingers until there is sufficient space between the two pads to allow you to re-install the caliper on the rotor. Once the caliper has been successfully re-installed place a few drops of Blue-Locktite (242) on each bolt and tighten each bolt between 28-38 pounds of torque. Once they have been tightened install the 1/4 inch twelve point socket and tighten the two lock pins that hold the pads in place.

After you have successfully accomplished all of what has been outlined above, top off the master cylinder if necessary by removing the master cylinder cover with a Phillips screw driver and replacing it when finished. Pump the brake lever until all of the air has been removed from the system. I have found that after pulling on the lever a number of times if you flick the lever a number of times you will notice that there will be little movement in the lever before full pressure can be applied to the pistons.

If you are interested in maintaining maximum braking performance as well as brake longevity it is recommended that you follow the above cleaning procedure every 2,500 miles. If you prefer having others service your motorcycle, please consider giving them a copy of this document and have them perform this process for you.