Your overhead garage door should operate safely and easily. If the tension cables on your door have broken, you will be dealing with deadweight when you are trying to open or lift the door. If you have a door opener and your tension cables are broken, the opener will not work. Over time the cables can just break. Once you fix the tension cables, you will be up and going again. There is nothing better than having a garage door that works properly.
Pull the emergency release on the garage door opener. Once you can manually lift and lower the door, lift the door to about 90 cm (3 feet) from the ground.
Attach vice grips to the side of the roller and track. This will keep the door from moving while you are working on the cables.
Take off the broken tension wire. Pop the wire off the bottom bracket using a flat head screwdriver. The tension will not be loose. Use a 9 mm (3/8 inch) spanner to loosen bolts on the drum, but do not remove the bolts. At this point the drum will spin. Spin the drum clockwise and remove the tension wire that you are replacing.
Insert the new tension wire into the place of the old one. Cut the tape off the new tension wire using scissors. Unroll the tension wire. Place the looped end around the bottom bracket. Run the tension wire up side of the garage door. Pull it through closest area to the wall. Loop the tension wire over the drum in the first deep grooved area. Slide the wire into the slot.
Spin the drum counter-clock wise and hold it while tightening the bolts using a 9 mm (3/8 inch) spanner. Remove the vice grips from the roller and track.
Check to be sure that the tension wire is snug. Lower the garage door. You should be able to feel the new tension wire holding the garage door in control.
Working on garage door is extremely dangerous. Use extreme caution and always work with a partner.