Hello comrade: With reference to the brake system of this truck you must first check that air pressure you have in the system, the valve that commands is the governor of air in which it is responsible for distributing the air to the other valves.
For this model, the general pressure is 9.50 bar to 10 bar
to get this pressure you must regulate the protection valve that is at the base of the air developer and depending on the value you take in the air gangster you must regulate it with an Alem of 4 on the regulation screw that is at the base of the dehumecator. Following this you must regulate the governor as follows:
Circuit towards the air deposits +0.50 bar above the cutting value, (that is, if you regulated the air passage to 9.50 bar you must enable the passage to the main tanks with 10 bar).
Accessory circuit with the same cutting pressure,
service brake circuit (the minimal pressure is regulated so that the blockade is welcomed is minimal 6 bar)
I hope you siva.
Ale