Fordson major diesel?

I have a fordson major diesel. i recently split the tractor between the cluch and gearbox 2 fix the gear box hand break. Once put back together i filled up the back end and the gearbox. after taking it up and down the road i checked the oil levels in the gearbox and the back end only to find that the oil level in the gear box had drop loads and the back end level was really high. i was wondering if the back end and the gearbox oil was connected or are they ment to be seperate? if they are ment to be seperate does anybody have an idea what the problem might be?