Gearbox / diff oil combined?
 

I have just been looking at a photo of a split impreza gearbox, the front diff and gear assembly seem to be in two separate 'compartments', does this mean the dip stick at the front of the box is simply for the front diff and the rest of the gearbox has separate fill & drain plugs?

Cheers for any info!

No just one drain plug and one fill. Later STi's actually have an oil pump inside the trans to help lubrication.

Does the oil have to be at a certain level to pass into the gear housing, i.e. can the gearbox run low and the diff still be ok?

I'm trying to work out what the whining noise is on a 94 WRX, I'm sure its the box, want to check every avenue before it comes out for a new layshaft bearing.

Only way to know whats wrong with the gearbox is to actually open it up. As long as your fluids have been changed per the FSM and is at the correct level every thing should be lubricated properly.
Just out of curiosity, setting at idle does the sound change with or with out the clutch pedal depressed?

There is no sound at idle, the sound only occours under load at speeds of above 40mph..

And when I say under-load all you need to do is merely apply the tiniest bit of throttle. As soon as you back off it disappears completely.

I've never seen anything like this, Normally a box will scream when coming down through the gears or when accelerating hard from a standing start. And diff whine normally occurs when not under-load and the vehicle is slowing.

[QUOTE=BVM]No just one drain plug and one fill. Later STi's actually have an oil pump inside the trans to help lubrication.[/QU

Later STis also have TWO drain plugs, the usual one under the front diff. and another which drains a sump below the gearbox. This plug is accessed by removing the plastic shield under the box. If you don't drain this one you'll leave about a litre of old oil in the box.
JohnD

Oh thats right! LOL I forgot about the 2nd plug on the STi box. Silly WRX owner I am!

what would this indicate? I have a slight whine that changes when the clutch is depressed.

If the noise dissapears when the clutch is pressed it could be the input shaft bearing, if the noise appears when the clutch is pressed it could be the clutch release/thrust bearing.