The detergent won't restore the color, and black dye is a huge pain to deal with, but one thing that you CAN try is go buy something black that is not colorfast (a new pr. of cheap black jeans, perhaps). Soak the non-colorfast item in a bucket of water for awhile until the dye runs a bit, then add your older clothes and then soak with it for a few days. Then do the vinegar trick. (This is essentially a deliberate form of a pink-undies laundry accident, and it may or may not work, but is probably worth a try.) They won't go back to being jet black, but the color may refresh a bit for you.
Also, for future reference, it isn't the washing machine that is fading your black clothing -- it is the dryer. From now on, once you've treated them with a vinegar wash, never put them in the dryer; hang them up to dry.