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2052006

Wheel Question?

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2052006

I fear this might be a bit of a silly question, but it confused me when it happened!

 

With the drivers wheel in the air (front o/s on axle stand) I started the engine and the wheel started spinning - not in gear - why is this? Is this to do with the differential, as it stopped when I depressed the clutch.

:o

 

Anyone enlighten me?

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jackherer

I believe its caused by drag in the gearbox, its perfectly normal behaviour. If you had grabbed hold of the wheel by hand it would have been pretty easy to stop it turning.

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jim21070

Yep, entirely normal diff action and friction caused the gearbox oil driving the gears around freely in the gearbox. Just enough power was being transmitted like this to spin the diff and driveshaft because it was "off load". I term this "windmilling" but this may not be the correct term for it. The effect you saw is the basis of an automatic gearbox torque converter whereby oil transmits torque between two turbine rotors.

 

One wheel spun because the diff has a natural tendency to transmit all torque to a wheel that is able to freely spin. You saw one did and the other did not. If one wheel can freely spin it gets everything and the other nothing. LSDs (Limited Slip Differentials) overcome this by transmitting some torque to the other wheel even if one wheel is spinning freely.

 

EDIT: Sorry Jackherer, I guess we were typing at the same time... Did not see your replay until I submitted mine :o

Edited by jim21070

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2052006

Cheers for confirming that!

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