Modern mountain bikes employ various braking systems, including disc brakes. Certain disc brakes use a hydraulic cable to interface the brake lever with the brake caliper. Bleeding the brake is a process whereby old fluid is forced from the brake line and replaced with fresh fluid. Tektro hydraulic brakes are bled whenever air has got into the brake line. Air bubbles cause the brake to feel "spongy", and ultimately lessens the brake's effectiveness.
Place the bike in a bicycle repair stand. Position it so the Tektro brake reservoir tank cover on the brake lever is parallel with the ground. If necessary, loosen the brake lever bracket mounting bolt with a 4mm hex wrench, and position the brake lever so that the reservoir tank cover is even with the ground.
Use a T15 Torx wrench and remove the two Torx screws atop the reservoir tank cover. Remove the tank cover from the reservoir.
Attach a bleed tube to the bleed nipple atop the Tektro brake caliper. Place the other end of the bleed tube in a receptacle, such as an empty bottle, to catch the brake fluid.
Fit a 7mm box end wrench around the base of the bleed nipple. Give the nipple a 1/8 turn to the left to open the bleed valve.
Squeeze the Tektro brake lever gently a couple times to force the old brake fluid into the receptacle. Add fresh brake fluid into the reservoir as the old fluid leaves the system. Keep the reservoir topped off with fluid to prevent bubbles from entering the system.
Check that no bubbles emerge from the bleed nipple into the tube. Only fluid should be emerging from the bleed nipple.
Close the bleed nipple with the 7mm box end wrench. Check that the reservoir tank is filled to the top. Add further brake fluid if necessary.
Replace the reservoir cover and Torx screws. Tighten the screws, using the T15 Torx wrench
Remove the bleed hose from the bleed nipple. If the Tektro brake lever mounting bracket was loosened to reposition the tank reservoir, move the brake lever to its original position and tighten the mounting bracket bolt.