Augustine believed that 1) the Septuagint was superior to all other translations, including Jerome's translation of the Hebrew Bible; 2) Augustine was concerned over the unity between the Latin and the Greek churches and 3) was also concerned people might leave the church after hearing a translation that differed from that which they have been accustomed to hear for generations. I think that Augustine thought the first reason was more important: he believed the church preferred the Septuagint and that its words, where they differed from the Hebrew, were inspired by the Holy Spirit. The following is a passage from the City of God (about 410) which Augustine argues the the Septuagint was superior. It was written after his correspondence with Jerome:
City of God, Book 18, Chapter 43
For while there were other interpreters who translated these sacred oracles out of the Hebrew tongue into Greek, as Aquila, Symmathus, and Theodotion, and also that translation which, as the name of the author is unknown, is quoted as the fifth edition, yet the Church has received this Septuagint translation just as if it were the only one; and it has been used by the Greek Christian people, most of whom are not aware that there is any other. From this translation there has also been made a translation in the Latin tongue, which the Latin churches use. Our times, however, have enjoyed the advantage of the presbyter Jerome, a man most learned, and skilled in all three languages, who translated these same Scriptures into the Latin speech, not from the Greek, but from the Hebrew. But although the Jews acknowledge this very learned labor of his to be faithful, while they contend that the Septuagint translators have erred in many places, still the churches of Christ judge that no one should be preferred to the authority of so many men, chosen for this very great work by Eleazar, who was then high priest; for even if there had not appeared in them one spirit, without doubt divine, and the seventy learned men had, after the manner of men, compared together the words of their translation, that what pleased them all might stand, no single translator ought to be preferred to them; but since so great a sign of divinity has appeared in them, certainly, if any other translator of their Scriptures from the Hebrew into any other tongue is faithful, in that case he agrees with these seventy translators, and if he is not found to agree with them, then we ought to believe that the prophetic gift is with them. For the same Spirit who was in the prophets when they spoke these things was also in the seventy men when they translated them, so that assuredly they could also say something else, just as if the prophet himself had said both, because it would be the same Spirit who said both; and could say the same thing differently, so that, although the words were not the same, yet the same meaning should shine forth to those of good understanding; and could omit or add something, so that even by this it might be shown that there was in that work not human bondage, which the translator owed to the words, but rather divine power, which filled and ruled the mind of the translator.
Source: Correspondence of Augustine and Jerome concerning the Latin Translation of the Bible
