Recently changed front to rear brake pipes after mot failure, bled all four bleed nipples on calipers but only rear brakes seem to be working , didnt bleed the valve on rear axle because of severe rust etc, I've cleaned and soaked it in penetrating oil ready for another attempt, could this be the cause of my problem? I've read several posts on the various sites saying cruiser brakes are a mare to bleed, any suggestions would be appreciated .