There is a thread on the other side at the moment about the viscous centre diff on the Four and it has me confued. So I thought i'd raise the same question here in the land of the straightforward answer

This description and this diagram explain pretty well how the centre diff works (clever stuff )

But to my mind it seems to describe a part time 4wd system. It claims the power only diverts to the rear wheels if the speed of the front wheels slip.

But we all know the GTFour is full time 4WD. So on a level surface with plenty of traction the torque will go to all 4 wheels equally. How is this if the diff only locks when the speed of the two ends is different?

I'm sure I'm missing something obvious but i dislike not understanding things. Can someone make it simple for simple me please?

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JDM ST205 (286bhp and 281lb/ft)
JDM ST202 (Finally sold )
1982 Pontiac Trans Am 5.7L V8 (See my website)

Paul,
When I had my Four on the G Force RR it was the first time they'd had one on their rollers. Initially the RR was set up for a mechanical centre diff but the computer got totally confused. When I mentioned that the Four had a viscous centre diff they changed the settings and it worked fine. The problem seems to be that the viscous centre diff allows a certain amount of slippage between front and rear wheels. This confused the RR computer. The same situation arises if an MOT centre attempts to test the brakes on one axle by using a 2WD RR. The centre diff will 'wind up' until it breaks. This also is the the reason why the owners handbook advises NOT to tow the vehicle with one axle on the ground and the other held rigid by the tow truck.

HTH

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Don
GT4DC Chairman
1994 Toyota Celica GT-Four ST205WRC JDM 269bhp @ 0.9bar
1994 Toyota Celica GT-Four Special GT 590bhp @ 1.8bar
1989 Van Diemen RF88/89 Formula Ford 1600
2008 Nissan Patrol GU 3.0L ZD30DDTi 154bhp

Cheers, Don.

Maybe i didn't phrase the question very well

I understand the reasons for not abusing the centre diff and how it'll lock up when the slippage happens, But according to what I have read the diff only locks when the speed at each end changes. IE when one set of wheels is slipping.

If this is the case then in ideal conditions the torque will all be going to the front wheels and the rear wheel will be coasting at the same speed. This would make the Four part time 4WD. Which I thought it wasn't.

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JDM ST205 (286bhp and 281lb/ft)
JDM ST202 (Finally sold )
1982 Pontiac Trans Am 5.7L V8 (See my website)

This site any good??

http://homepage.ntlworld.com/williams73/LRWindUp.htm

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ST205 WRC #0002249

Cheers mate

The penny has dropped. I now understand all things and I'm off to subjugate the earth

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JDM ST205 (286bhp and 281lb/ft)
JDM ST202 (Finally sold )
1982 Pontiac Trans Am 5.7L V8 (See my website)

Daz,

Thats a really good link!

Think I am going to bookmark that one.

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Loosey
Loosey@gt4dc.co.uk
Storm Blue JDM ST205
Super White JDM ST205
http://www.gtfours.co.uk

Some people are like a Slinky .. Not really good for anything, but they make you smile when you shove them down the stairs!

It is isn’t it, you do come across the odd link now & then that are really good & this guy really knows his stuff.

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ST205 WRC #0002249