In a large bowl, dissolve yeast in warm water. Add the sugar, eggs, oil, salt and whole wheat flour; beat until smooth. Add enough all-purpose flour to form a soft dough.
Turn onto a floured surface; knead until smooth and elastic, about 6-8 minutes. Place in a greased bowl; turn once to grease top. Cover and let rise in warm place until doubled, about 1 hour.
Punch dough down. Divide into nine pieces; shape each piece into a 14-in. rope and braid three ropes together. Place in three greased 8x4-in. loaf pan. Cover and let rise until doubled, about 30 minutes. Bake at 350° for 40-45 minutes. Remove from pans to cool on wire racks.