What if you stopped grading, just for one unit of study? Don't put a number, percentage or letter on an activity, project, quiz or test.
How would you evaluate your students? Is it even possible?
What would replace the grading?
Would you speak to your students more? Could they evaluate each other? Themselves?
Three or four weeks.
Change what you do.
What's holding you back?
Could it be a fear of learning that you never needed the grades in the first place?