Second part of fighting behind tank's wheel will surprise you with new, dangerous enemies: big, red robots that resemble spiders (#67). They are called Harvesters. Few shots from cannon should be enough to defeat the opponent (aim in the head). Harvesters attack mainly with machine gun. From time to time, they'll fire rockets in your direction too. Use machine gun to destroy them. Beware of big hole, located nearby. If you drive into it, Kane will immediately die.
When the Nexus building appear in front of you after the longer driving (#68), you will have to fight with two Harvesters (#69) at the same time. Robots will destroy one of the towers (field of the maneuver will limit considerably). The best way to destroy opponents is to stop near the ruins and shoot at every of machines to the bitter end. Traditionally, use machine gun to destroy rockets and hit Harvesters from the cannon.
After the fight, drive in the building through the huge hatch. Once inside (#70), you'll have to get out of the tank and approach the comrades waiting for you. Go on the platform (lift) to finish this stage.