From The Winston Effect book: Terminator 2 opens with the future war sequence, and the classic shot of an endoskeleton's foot crushing a child's skull. "That is one of the shots you always see from this movie." said Winston. "The skull is crushed, the camera moves up to the endoskeleton's head, with it's glowing eyes, and it's head turning this way and that, looking for it's next victim. That was a full blown animatronic robot! And it was a very big advancement over what we had done for the first Terminator.
A team of twelve puppeteers standing off-camera operated a series of cables, rod and radio controls to create the endoskeleton performance in the opening shots -- some on the crushing leg, some on the waist twist mechanism, some on the neck, some operating a hydraulic bicep action, and others on the various head and eye movements. "This tracking shot moves up to the child's skull buried in the dirt." explains Mahan, "and then the foot smashed down on top of it, and the camera pulls back to reveal the whole endoskeleton. So the illusion is that this endoskeleton has walked up and stepped on this skull. How it worked, though, was that the endoskeleton's left leg was planted on the set, and it's right leg was smashed down on the skull with a rod that was connected to the calf, which could then trigger release so that the guy operating it could grab the rod and get out of shot before the camera moved up. It was a five-or six-foot rod, so the puppeteer was pretty well out of frame anyway. He could just hoist it up, smash the leg down, pull it out, and step back out of the shot as the camera moved up.
You appear to have these fixed ideas that the full sized T-800's were all built identically in both movies, but that obviously isn't the case if you carefully study the original T1 photos I posted and compare them with the T2 versions. Start from the feet up and you'll soon see the obvious differences... The T1 T-800's have cruder build quality and less articulation than T2 T800's. Notice the ankle articulation and feet design? The shape of the fingers/knuckles and the mock pistons and wiring. The T2 skull design looks meaner and more intimidating -- well, that's a matter of opinion, but you get the point, I hope.