Bristol 25 tractor
Only after experencing some aerial acrobatics on our Bristol 25
tractor we discovered that it lacked some basic safety features
such as adequate brakes.
Brakes that the Bristol 25 tractor is equipped with are suitable
only on the near-flat land. They are not capable of holding the
tractor on a slope.
Hence, if the engine stalls going up (or down) a steep slope there
is no way of restarting it safely. There is also no way of safely
changing gears in a steep terrain.
If the gearbox accidentally disengages when climbing or descending
a steep slope - the tractor rolls out of control and there is
little an operator can do.
Fig 1. Tractor track ratchet brakes.
improve the situation we installed a ratchet brake system that
works directly on both steel tracks. The system system is installed
on the roller cage and does not modify the Bristol 25 original
design. As can be seen in Fig 1. we modified a car trailer axle
to support the ratchet bar.
When in use, the ratchet can block either forward or reverse roll,
allowing only uni-directional motion of each track. It means that
when the ratchet is in the position depicted in Fig 1. the tractor
can climb a steep hill, but cannot roll back even if the gearbox
disconnects to neutral gear.
The ratchet brake also serves as a parking brake enabling an operator
to leave the tractor and restart the engine in almost any situation.
Fig 2. When not in use the ratchet bars are supported in vertical
position using nylon straps.