Landgruiser 100 centre diff lock.

Hello Ken and Aileen,
My basic and not proffessional answer to your questions are as follows. Firstly the centre diff on constant four wheel drive vehicles shuffles the drive from front to back as necessary. By having different diameter tyres on the front and back makes this diff work far more than is necessary and MAY lead to premature centre diff failure. The service manual says to rotate the tyres every 5000 kms to make sure that the tyre diameters remains as even as possible.
When the centre diff is locked, the drive train makes the front and rear wheels turn at the same speed and distance but turning corners or having different diameter tyres then the actual distance that the wheels travel is different. Something has to give. On gravel roads the tyres slip on rocks, sand etc and no wind up occurs but if the vehicle is driven on a tarred road then there is no slippage and the pressures created by having the front wheels travel a different distance to the rear winds up in the drive train. Slight wind up makes steering harder and as you say it is hard to get the vehicle out of four wheel drive. Tyres will scrub and in extreme cases damage can be done to axles, diffs and the ultimate failure is to have the transfer case split. Wind up is definitely bad for the vehicle.
In your case, starting on a hill and driving for 200 metres is something that you alone can decide. Providing you travel for a short distance in a straight line and the tyre diameters are the same then the wind up is not severe. (Not desireable but not severe). I know that these criteria are not always available. Driving with one set of wheels in the gravel is also acceptable as these wheels can slip. I guess (but do not know exactly) that it would be possible to put in a switch to stop the centre diff from being locked but my basic opinion is that someone with more knowledge on the subject than me decided that it is the way to go. I would not change it. Murphy's law says that the time you really need to have the diff locked the switch would be off and you would get into trouble.
I am pretty sure that the diffs on the cruisers are not weak. The thinking is that if you need low range then you need four wheels driving. You do not have four wheels driving if the centre diff is not locked.
Hoping this answers your question. Members with automatic gearboxes will probably be laughing at us members with manuals. I have ordered a BT and will find out about the clutch slipping later on next year.
Anyway, anyone with proffessional knowledge may enlighten us further.
Regards
Colin and Val
Merry Christmas to all

Hi Ken and Aileen,

I know this refers to an 80 series but it may well be the same setup.

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David.