Fruit always dies

I have 8 grape vines of several varieties that I planted about 10 years ago.  I'm in western Pennsylvania where we usually get a reasonable amount of rain, not too much or too little.  There are a few inches of topsoil and then it's all clay.  For all of the vines each year the fruit sets properly but after it gets about half grown it all dies.  The plants seem healthy enough.  I spoke to one person who thought it might be caused by a soil deficiency.  Does anyone have an idea what might be going on with my grapes?  I'd love to get even a few nice bunches to enjoy one of these years.

But some fruit never really lives...

I'd start by giving them 2" of good compost top dressing every year from 6" out from the trunk to the dripline.

Welcome to Permies Mark!

It sounds like black rot to me.

Do you know what some of the grape varieties are that you have, some are more susceptible than others.

If you have some photos that would be helpful also.

Sounds like lack of water to me, do the leaves prematurely yellow also?

Do you mulch the pruned vines around the base of trunk every year?
It might also be that the vine roots can't penetrate the clay layer, this is like they are in a shallow pot.

I echo the previous call for compost... you could also plant comfrey/daikon/burdock near the trunk to help break up the clay layer.