is Adam no longer the son of God? Luke 3:38 (KJV) states (emphasis added):


  which was the son of Enos, which was the son of seth, whcih was the son of Adam, which was the son of God" .


The verse uses the past tense. Does that indicate that Adam is no longer a son of God? 

When Jesus was speaking to the Sadducees in Mark 12:26 (KJV), emphasis added, He said:


  God spake unto him, saying, I am the God of Abraham....


Which is present tense and shows Abraham is still alive. Since the bible is using Adam "was" the son of God, does this mean Adam is no longer a son of God?
This is an artifact of the translation you are using. There is no verb in the Greek text of the verse. Consider this version:


  the son of Methuselah, the son of Enoch, the son of Jared, the son of Mahalalel, the son of Cainan,  the son of Enosh, the son of Seth, the son of Adam, the son of God. [Luke 3:37-38 NKJV]


Notice that the NKJV (like many other translations)  places the son in italics. This indicates that the words were added to make to text read more like English. Some other translations go further and add something like 'who was'.

The Greek version is more terse, reading something like "... Enosh of Seth of Adam of God"

The passage in no way suggests that Adam is no longer of God.