Front Brakes Hardly Working

On my '71 Scamp Manual disc on front drums in rear. 71K miles rear brakes seem to be doing all the work and will lock up when applied hard. The rears are not over adjusted and don't need replacement it is all clean back there and appears to be working as it should. I have bled the calipers and they bleed fine but same result.
I was going to rebuild the calipers with seal kits but for them both to act the same is weird I think so I don't want to buy new calipers either. Is it possible the proportioning valve could allow more fluid to the rear than the front? Any thoughts would be helpful.
I'm going to remove a caliper and have someone apply the brake and make sure the pistons move enough and see if its a piston issue.