PR 776 - Modern, infinitely variable drive concept: World's first hydrostatically powered crawler tractor in the 70 tonnes category: Liebherr PR 776. Another key advantage of hydrostatically powered crawlers when working in restricted spaces is the excellent manoeuvrability with continuous power to both tracks. With an optional GPS navigation system, the work progress and the surrounding area can be visualized. increasing machine productivity and minimizing operator stress and strain.