A few things spring to mind:
1) There should be a small hole in the top of the bush to allow grease through from the king pin to provide lubrication to the brake cam bush. Did you drill the hole?
2) After pressing the bushes into the stub axle, they should be reamed to suit the cam diameter. You'll need a hand reamer to do this job. Otherwise the fit is very "hit or miss".
3) Sometimes the shoe return springs are stretched and weak, new ones are available from specialist suppliers.
1) There should be a small hole in the top of the bush to allow grease through from the king pin to provide lubrication to the brake cam bush. Did you drill the hole?
2) After pressing the bushes into the stub axle, they should be reamed to suit the cam diameter. You'll need a hand reamer to do this job. Otherwise the fit is very "hit or miss".
3) Sometimes the shoe return springs are stretched and weak, new ones are available from specialist suppliers.