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[alfissimo]

What is it exactly that causes that judder on a P4 when full-lock is applied? I know it's something to do with rotation speed through the viscous coupling, but would someone mind explaining exactly what causes it? I'm not technically minded really, but very intrigued to know...
The only way to cure the problem is to have the floor-pan stregthened isn't it?

[tvatavuk]

Hi,
P4 don't have real central differential which would allow front and rear wheels (in this case propshafts) to rotate at different speeds as needed.
While cornering front wheels go slower and do less road travel then back wheels which follow front wheels but in larger circle diameter. Closer you are to full lock of steering wheel greater difference between front and rear speed/road travel it is.
All this is leading to different rotation speeds of front and rear propshaft which are connected to viscous coupling. Once roatation difference is enough Visco coupling will harden leading transfering more then nominal 5% of torque to back. So now you have rear wheels which are trying to go faster and viscous coupling which is trying to force rotation speed of rear to match front. This will lead to forcing rear wheels to skip small portions of ground. All the forcing and skiping will lead to shakes in propshafts and visco coupling thus transfering noise and earthquakes to chasis
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Tino Vatavuk
Little black dress which replaced Alfa Romeo 33 S 16v Permanent 4 GMo

[paulhide]

If you're on full lock with drive going to all four wheels (ie the viscous coupling is locking to engage the rear wheels) there is a problem in that the outer wheels are moving further than the inside wheels. Slip diffs sort out lateral movement diferences, but there is no compensation for the difference between front and back wheels on either side, so on a dry smooth road you get a bit of wind-up. (why-nd)
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Owner's Club 33 Registrar. Now from P4 & S2 1.7 QV
http://www.alfa-pages.co.uk/viewtopic.php?t=5188