Toyota Prado 4WD- Use of 4wd on sealed roads.

completely un-necessary if you can get it to unlock.

I thought the outside wheels travel further than the inside wheels.

They do! But the outside front travels further than the outside rear and the inside front travels further than the inside rear. Side to side doesn't matter is the diffs are open. Its the difference between front and rear with the centre diff locked that causes wind-up.

You can with the 80, 100 and 105 series if you do the "7 pin mod" it will only lock the centre diff in high or low if you push the button. There are different ways of doing it. One is the 7 pin mod under the dash if you have ABS and if you don't you can simply undo a connection on the transfercase that activates it when low is selected.
Maybe the prado can have something similar done ask the guys on LCOOL. You can search the 7 pin mod there to get the idea of what I'm talking about with the cruisers.

Dave,
Its depends on which model Prado. Some of the 120series have mechanical engagement and some are electronic. Can't do anything about the mechanical engagement. But the way I understand it, with the electronic engagement you can already use low range and the centre diff only locks when you press the dash button.

cheers
phil

Being 1996 Prado it will be the 90 series. It has a lever to select 4WD-lock and 4WD-Lo. I've never actually checked but I've heard it is still an electronic lock (rather than mechanical) although it is activated by shifting the lever.

There is no separate button to lock the centre-diff, so if you modified it to not automatically lock when Lo-range was selected, you'd have to install a separate button to lock the centre diff.

A friend of mine modified the family 80 series 'Cruiser and he found while it was helpful to be able to use lo-range to manoeuvre the caravan into positiion without tearing up the campsite (ie. centre diff unlocked), virtually every other situation which required lo-range also required the centre diff to be locked - eg. when ascending a hill steep enough to require lo-range, the front wheels would just slip unless the centre diff was locked. I think in the end he decided the mod hadn't been worth the effort.

Tim, there were 2 systems on the 90series as well. The VX/Grande had push button centre diff lock while the GXL and RV have what you describe.
Shaker's comment was for his 120series.

He only drove 4 kilometres with it locked.

His 90series has a mechanical centre diff lock - engaged when you pull the lever - its different to the 80series.
Anyway, that wasn't the original poster's problem.