Hey Leonardo,

if the pump is working and puts up pressure, the whole system is filled up with oil, the only reason left why the rear end doesn't comes up is imho a valve issue.... or closed in air witch can't come out (Pump is working against an air bubble and so doesn't get enough compression to lift the car hind end).
So, I would say check all the valves in the system if they open and close the right way, be sure there is no air left in the system AND check the electricity on the Valve circuit.

Cheerio

cu Conny [AK]
560SE, 560SE, 420SE.