Shimano 105 refers to a group of bicycle components designed for use with road bikes. Included among these components is a pair of integrated shifters (a single unit “integrates” both shifting and braking capabilities). Each shifter/brake lever fits onto one end of the bicycle handlebar, and once positioned also doubles as a potential hand rest. Before beginning installation of the brake lever, be sure all grip tape is removed from the handlebar--the levers cannot be installed with grip tape still in place.
Fold back the brake lever hood to reveal the installation nut inside.
Loosen the installation nut, using a 5-mm Allen key, turning it counterclockwise until the clamp on the underside of the shifter is wide enough to slide over the end of the handlebar.
Slide the appropriate lever onto the handlebar. The two levers are not alike, so be sure you’re placing the left-side lever (which controls the front brake and gears) on the left of the handlebar, and the right-side lever on the right of the handlebar. There is a small paddle control behind each brake lever--the surface of this control should face away from the inside of the bike.
Position the lever on the handlebar to give you a comfortable reach. Be sure the head of the lever is straight--it should be perfectly even with this portion of the handlebar.
Tighten the installation nut inside the lever. This will fix the underside clamp onto the handlebar.
Repeat the above steps for the second shift lever. To position the two levers at equal height, place a spirit (or bubble) level across the hoods of the levers, and adjust the height of the second lever accordingly. Once the height is correct, tighten the installation nut inside.