was out this weekend up the mountain in the welsh valleys

was great day out intill i noticed my mates sj rear wheel sliding out of the diff shaft
i had to jack it up every hundred yards and pop it back in
luckly it happend wen we got to the farm track
he recently had two new wheelbearings and rear drum shoes
could the bearing callaps the first time out????
is ther anything els than the bearing that keeps the axle in the shaft?
thanks
richy