Do you have a service manual? They are pretty handy.
My pal had this same issue and I have given this same answer to others and it helped them. He chased it and chased it trying to find the issue with the brakes, shoes, cylinders, springs, etc. It wasn’t the brakes at the drums at all. It was the adjustment on the push rod of the master cylinder. He got it adjusted properly by an old boy shop and the issues disappeared. Check this. It likely is contributing to your issue, or might be the real problem.
Last edited by Fox; 04/18/2021 4:55 AM.