16-12-2020, 05:23 PM
Update time ! I have now adjusted and measured my brake setup with late Austin rear and Semi-Girling front, together with the compensated cross shaft. I hope these notes might help anyone doing the same task. I can measure angles and free play fairly accurately, but efforts and tensions (i.e. the bit that matters) are hard to measure and therefore only approximate. I used a lever bolted to a scrap wheel which I could stand on. If the wheel doesn’t turn with my full weight applied, I know the braking effort is at least 180 lb. The photo below shows the cross shaft action viewed from the offside. To get things right, I needed an adjustable front cable which was set for a total length of 72.5 inches.
At rest, the balance lever on the outer shaft faces forwards at 23 degrees to the vertical, whereas the forked lever on the inner shaft sits at 20.5 degrees. The gaps to the forked lever are zero at the front and 0.25 inches to the rear. The handbrake roller has no clearance to its mating lever on the inner cross shaft.
If the footbrake is “enthusiastically” applied, the outer shaft moves round to 12 degrees to vertical and the swinging balance lever turns a little clockwise as it does its job. Pedal travel is just under 3 inches until the foot effort is about 150 lb. Pedal reserve travel is at least 1 inch. The gaps to the forked lever are now equal, at 0.12 inches each side. The front cables are pulled back by 0.8 inches, until their tension is about 190 lb giving 300 lb braking per wheel. Simultaneously, the rear cables are pulled by 0.4 inches until their tension is 120 lb giving 170 lb braking per wheel. As you might expect, cable tension is rather low whilst the slack is being taken up, then rockets up with very little further movement. The outer and inner shafts rotate by 11 and 8.5 degrees respectively. The levers at the wheels move by about 20 degrees at the front and 10 degrees at the rear.
Handbrake operation is rather different, as the compensator doesn’t move. Near full application of the handbrake (which bears on the inner shaft) moves both shafts by 8 degrees. The front cables are pulled back by 0.5 inch, until their tension is about 30 lb giving 25 lb braking per wheel. Simultaneously, the rear cables are pulled by 0.38 inches until their tension is 100 lb giving 140 lb braking per wheel. Handbrake lever movement is about 3.5 inches or 5 clicks, and the hand effort is about 30 lb. Clearly, the lion’s share of handbrake action is to the rear wheels, with the fronts giving a bit of a “top up”
I am pleased that the new shaft has given a change towards greater braking at the front, which should solve the previous rear lockup effect. The compensator always has clearance to the fork, so front cable travel is no longer being restricted by the rears “going solid”. Once some better weather returns I plan a road test with a Tapley meter.
At rest, the balance lever on the outer shaft faces forwards at 23 degrees to the vertical, whereas the forked lever on the inner shaft sits at 20.5 degrees. The gaps to the forked lever are zero at the front and 0.25 inches to the rear. The handbrake roller has no clearance to its mating lever on the inner cross shaft.
If the footbrake is “enthusiastically” applied, the outer shaft moves round to 12 degrees to vertical and the swinging balance lever turns a little clockwise as it does its job. Pedal travel is just under 3 inches until the foot effort is about 150 lb. Pedal reserve travel is at least 1 inch. The gaps to the forked lever are now equal, at 0.12 inches each side. The front cables are pulled back by 0.8 inches, until their tension is about 190 lb giving 300 lb braking per wheel. Simultaneously, the rear cables are pulled by 0.4 inches until their tension is 120 lb giving 170 lb braking per wheel. As you might expect, cable tension is rather low whilst the slack is being taken up, then rockets up with very little further movement. The outer and inner shafts rotate by 11 and 8.5 degrees respectively. The levers at the wheels move by about 20 degrees at the front and 10 degrees at the rear.
Handbrake operation is rather different, as the compensator doesn’t move. Near full application of the handbrake (which bears on the inner shaft) moves both shafts by 8 degrees. The front cables are pulled back by 0.5 inch, until their tension is about 30 lb giving 25 lb braking per wheel. Simultaneously, the rear cables are pulled by 0.38 inches until their tension is 100 lb giving 140 lb braking per wheel. Handbrake lever movement is about 3.5 inches or 5 clicks, and the hand effort is about 30 lb. Clearly, the lion’s share of handbrake action is to the rear wheels, with the fronts giving a bit of a “top up”
I am pleased that the new shaft has given a change towards greater braking at the front, which should solve the previous rear lockup effect. The compensator always has clearance to the fork, so front cable travel is no longer being restricted by the rears “going solid”. Once some better weather returns I plan a road test with a Tapley meter.