Yesterday, 05:08 PM
Hi
It is an age-old A7 effect to have the OSR "stronger" than the NSR on the footbrake. It's nice and symmetrical on the handbrake, because that pulls on the centre of the cross shaft.
On the earliest one-piece cross shaft the footbrake actuates one end, so the OSR is actuated directly, but the NSR is via a springy cross shaft. Springy ? I hear you say, but isn't it a mighty chunk of unbendable steel ? Well in the world of cable brakes it's torque and tension that matter - visible movement is of little consequence. Just an invisible degree or so of twist in that cross shaft is enough to upset the balance in rear cable tension.
Later cross shafts had a larger diameter hollow outer on the OS, the pedal force travels down this to the centre where a weld joins it to the main cross shaft. Only problem is that the differential movement is so small that the zinc lined bearing on the OS (very hard to see) siezes up and the whole thing becomes no better than the earlier type. If the individual levers on the OS touch each other you get the same effect. Any wear in the OS bearing will have a similar effect, as fore-aft movement just allows pedal force to be communicated direct to the OSR cable.
The final and best design iteration was the semi-Girling cross shaft, with a bearing at both ends of the outer tube and more differential movement. This design does of course have compensation from front to rear, and distributes tension 60% to the front and 40% to the rear. Only snag is reduced ground clearance.
It is an age-old A7 effect to have the OSR "stronger" than the NSR on the footbrake. It's nice and symmetrical on the handbrake, because that pulls on the centre of the cross shaft.
On the earliest one-piece cross shaft the footbrake actuates one end, so the OSR is actuated directly, but the NSR is via a springy cross shaft. Springy ? I hear you say, but isn't it a mighty chunk of unbendable steel ? Well in the world of cable brakes it's torque and tension that matter - visible movement is of little consequence. Just an invisible degree or so of twist in that cross shaft is enough to upset the balance in rear cable tension.
Later cross shafts had a larger diameter hollow outer on the OS, the pedal force travels down this to the centre where a weld joins it to the main cross shaft. Only problem is that the differential movement is so small that the zinc lined bearing on the OS (very hard to see) siezes up and the whole thing becomes no better than the earlier type. If the individual levers on the OS touch each other you get the same effect. Any wear in the OS bearing will have a similar effect, as fore-aft movement just allows pedal force to be communicated direct to the OSR cable.
The final and best design iteration was the semi-Girling cross shaft, with a bearing at both ends of the outer tube and more differential movement. This design does of course have compensation from front to rear, and distributes tension 60% to the front and 40% to the rear. Only snag is reduced ground clearance.
