31-07-2020, 06:38 PM
Austinwood raises an interesting point (apologies to morrisminor if I am drifting off topic)
When the brakes are applied, there is a small amount of twist in the front axle and bend in the radius arms due to the torque reaction and this has the effect of slackening the brake cables. This was probably true even for cars when they left the factory. If certain components have wear, the whole axle can also move backwards fractionally as the cable tension takes up any clearance.
When the front brakes are tested on a rolling road, these two effects are still present, so the front brake effort reading is true. When the back brakes are tested, any backward front axle movement due to wear will still be present. However, the front torque reaction/axle twist is now absent so the front cables are tighter than they would be on the road. Due to the lack of any front/rear compensation mechanism, the tighter front cables tend to result in looser rear cables. The rear brake effort reading will therefore be a little less than true. So I agree that in effect the front readings are flattered.
With the introduction of semi-girling brakes on the ARR Ruby, the radius arms and their axle attachments were strengthened to better resist axle twist. Also, a swinging arm compensator was fitted to the cross shaft, so the front and rear cable tensions are immune to cable movement and forced to be equal.
As far as I am aware (happy to be corrected), the lengths of the various levers in the semi-girling sytem are the same for front and rear, and the brakes are the same, so the braking effort is equal front and rear and can't be changed by cable adjustment. Considering that the Ruby is front heavy, and even more so under braking, there must be a risk of the rear brakes locking under slippery conditions if applied too enthusiastically.
When the brakes are applied, there is a small amount of twist in the front axle and bend in the radius arms due to the torque reaction and this has the effect of slackening the brake cables. This was probably true even for cars when they left the factory. If certain components have wear, the whole axle can also move backwards fractionally as the cable tension takes up any clearance.
When the front brakes are tested on a rolling road, these two effects are still present, so the front brake effort reading is true. When the back brakes are tested, any backward front axle movement due to wear will still be present. However, the front torque reaction/axle twist is now absent so the front cables are tighter than they would be on the road. Due to the lack of any front/rear compensation mechanism, the tighter front cables tend to result in looser rear cables. The rear brake effort reading will therefore be a little less than true. So I agree that in effect the front readings are flattered.
With the introduction of semi-girling brakes on the ARR Ruby, the radius arms and their axle attachments were strengthened to better resist axle twist. Also, a swinging arm compensator was fitted to the cross shaft, so the front and rear cable tensions are immune to cable movement and forced to be equal.
As far as I am aware (happy to be corrected), the lengths of the various levers in the semi-girling sytem are the same for front and rear, and the brakes are the same, so the braking effort is equal front and rear and can't be changed by cable adjustment. Considering that the Ruby is front heavy, and even more so under braking, there must be a risk of the rear brakes locking under slippery conditions if applied too enthusiastically.