A bridle strap or bridle tape is an action part found in upright acoustic pianos and Rhodes pianos. It consists of a fabric strap that has a leather end with a punching in the centre. Its function is to aid in movement of other action parts.
Upright Pianos:
On upright pianos, one end of the bridle strap is glued or fixed to the hammer butt, and the other is attached to the end of the wippen via a steel wire. The strap is usually white with a red leather end, though this can vary. The hole-punched leather end can be removed by disconnecting it. The bridle tape’s role is to aid in the resetting of the action after the key has been released. When the hammer has struck the string the catch of the hammer butt rests against the back check, locking it into place. When the key is realised by the musician, the wippen and the hammer butt fall back into rest position due to gravity. As the wippen falls, it pulls on the bridle strap, making the hammer return faster.
Technically the bridle strap isn’t strictly necessary for the returning of the action parts to work; and there is debate in the piano technician community as to how effective bridle tapes are in a properly functioning action. They are useful however when hammers are not regulated properly or are a bit slow – then the tape helps in pulling the hammer down quickly so the key can be restruck.
The other secondary use bridle straps have is keeping the lower action in place when the action assembly is removed from the piano. Without the straps, when the action is lifted out the wippens will sag. This makes realigning them difficult when the action is reinserted into the piano. This is because the jack blocks the lower action from being inserted correctly. Bridle tapes eliminate this issue.
Rhodes Pianos:
On Rhodes pianos the bridle strap is located on the end of the hammer cam, and is connected to the damper arm. The strap is light green in colour, with a dark green leather hole-punched end. In a Rhodes it performs an essential function, which is to lift the damper arm when the hammer cam is lifted by the key. It is a critical part of the action because of the tape is loose or broken then the damper arm will not lift, which will not allow the tine to sustain. Therefore good regulation and condition of the bridle tapes and damper arms is key to properly functioning and even touch of the action.
The straps can be removed from the damper arms, which is required when removing the hammer cams or installing the ‘Miracle’ or bump modification to the keys.
The damper arm should have roughly 1/8” of lost-motion when the key is pressed before the bridle strap pulls the damper arm, and the damper starts to lift off the tine. This can be regulated to allow a slightly lighter or heavier touch depending on the amount of lost-motion needed.
Broken bridle straps should be replaced, and the new ones should be measured and attached at the exact same spot as its neighbours to minimise the amount of further regulation needed.
