Yes and no. Black in Northern areas became Democrat (as did their White counterparts), but a good reason for that was because they had little choice in the cities. If you valued your job, your livelihood, etc., you had to support the Dem cause. Witness Chicago, which had a huge Black GOP body, and from the ‘30s until the ‘60s, it gradually declined to nothing. However, Blacks in the South, those that could vote, remained heavily GOP for 3 more decades past their Northern counterparts (but because so many were prevented from voting, or only allowed to do so under certain circumstances, only a modest number of Black elected officials existed, and none in the legislature until the ‘60s, when they had become Democrats by and large).
In the Emerging republican majority Kevin Phillips pointed out that the South did indeed have a higher GOP proportion of blacks than the north. But, Not a big minority much less a majority. They were Dem’s to from my recollection.