One of the most common repairs I run into is that of broken bridle straps. These straps are made of a thin cloth that becomes dry rotted over time and are usually the first things to go bad in a piano. Broken bridle straps can also serve as a good warning sign that other problems might soon arise in the piano action. Luckily, replacing bridle straps is one of the quickest and easiest repairs you will run into.
The bridle straps have a cork end that is pushed into a hole in the catcher which is attached to the hammer butt. The other end of the strap is slipped over a wire that is attached to the whippen (the whippen transfers force from the key to the hammer, as well as to the dampers). The purpose of the bridle strap is make removing and reinstalling the piano action easier. The straps keep the whippens from hanging down loosely which can cause them to catch on the key capstans and break when the action is put back in the piano. The straps can also help the hammers return to rest in a poorly regulated or sluggish action.
The cork end of the broken straps can easily be popped out of the catcher with a simple tool made from a bicycle spoke or other thick wire..
New bridle straps, as well as the tool to insert them, can be purchased from any piano supply warehouse such as Schaff (also known as Vanda King) or Pianotek. They are only sold by the set, not individually. This is usually fine because they are cheap and it is a good idea to have extras on hand.
The cork tips stick onto the end of the tool which can then be pushed into the hole in the catcher.
The other end can then be hooked onto the wire coming out of the whippen, and that's all there is to it.