Take the old disc and have them put on a Lathe Machines and see if they are warped or not if they are have them lathed
and then fit and try again .
Warped disc if with in the limits can be lathed ,you don't have to replace them.
Now if they do warp again then check the calipers are not binding ,what can happen is when the brakes bind the disc get hot and when you pass over water it will shock and warp the disc.
When you have the disc removed disconnect the tie rod from the knuckle so its free to turn . and test the preload .
If not with in spec you will have this same affect when braking thinking the disc is warped .
If not with in preload specs the swivel bearings will need to be checked adjusted or replaced .
For further assistance with this issue please get back to me with the reply box below .
This is not a one answer and done i/we will stay with you until the problem is sorted out .
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