Well after pulling the y axis screw I replaced the thrust bearings and rebelled the screw. The screw had 6.34mm balls in it and replaced them with 6.35mm.
The screw back lash went from 0.02mm to less than 0.01mm maybe 0.008mm.
I still had 0.01mm movement on the end of the screw even with a 0.05mm shim between the thrust bearings. I then replaced that shim with a 0.07mm shim and that didn't seem to make a difference. Still 0.01mm screw movement. I put a dti on the thrust bearing housing and failed to notice any movement so it has to be in either the bearings still or the bearing cap near the coupling.
I think I will remove the motor and coupling half and see if I can get some movement out of the bearing cap. If no movement then I will add a thicker shim between the bearings and see what happens.

All in all so far a great result as backlash setting has gone from 30 to 7 so considering it was 5 from the factory I think this is ok for an old screw.