[Cliffde]

First you have to check all conditions a hydraulic system needs.
enough oil, a good filter, clean tank, no water in it, a good working pump (Volume and pressure) and a working mechanic.
At the working mechanic you have to check the lever you control by hand and all levers which belong to the regulation system. If you lay under the trac you can see several mechanical parts which combine the back linkage and the hydraulic control unit. You can make some settings at this mechanical parts when you choose position or draft.
When all this requirements are o.k. and the system doesn´t work, then you have to take out the control unit or have to open it. Perhaps it´s better to open it bevor taking it out. Perhaps you can find a broken spring or something.

Look after all conditions, try position and draft and then lets talk again...

@ Hartmut:
Without beeing friends (you and your English) you can improve it by speaking and writing. Your english is quite well!

Greetings Cliff

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Becaus of the air:

Hartmut tried to tell you about your air compressor. Normally you have an air compressor on the right side of the engine. Some tracs and also Hartmuts have an added air compressor driven by belts.
But, what he wanted to tell you is, that when you add some turbo-charger for the combustion eventually you have to fix the suction hose of you regularly air compressor to the suction line of your turbo and not to the pressure line of the turbo.
The air compressor is only used to self-suction and not to beeing loaded. We don´t know whether it could be a problem to load the compressor or not. But in any case it´s better to let it work normally (self-suction).
Somebody thought if you load the compressor by turbo it would load up the tanks faster (but it´s more a joke than something else)...

Greetings