The Stovebolt Site Forums The Parking Lot Big Bolts air disc brakes, input wanted

on a tandem axle tractor you could legally order no steer axle brakes until the mid eighties. after that brakes are required on all 3 axles. single axle tractors were required to have steer axle brakes those sometimes came with a limiting switch which would hold the pressure to a maximum 10 lbs to front brakes in slippery conditions. not sure when they outlawed that switch