Rear wheel movement question

rodisi

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E220CDI 1999 W210
The car is off the ground. I rotate the left wheel, the right wheel immediately starts moving the opposite way. I rotate the right wheel, the left wheel doesn't move until I move the wheel very fast. Does that sound right?
 

LostKiwi

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Nothing to worry about. Presumably the gearbox is in neutral.
It's all down to slight variations in friction in the differential components.
 
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rodisi

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Thank you @John Laidlaw and @LostKiwi. A weight off my mind. I've never done anything to the differential and thought maybe it's payback time.
 

L John

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The car is off the ground. I rotate the left wheel, the right wheel immediately starts moving the opposite way. I rotate the right wheel, the left wheel doesn't move until I move the wheel very fast. Does that sound right?

As Stwat says it's normal.
With a manual box that's in gear (any gear) with the engine stopped, the driveshaft can't move. When you turn one wheel, the other will turn in the opposite direction and at the same rotation speed as the diff gears do their magic.

In an automatic things are a little different and I'm not familiar with it, was yours in park or neutral when you did the test?
I'm a little surprised that each side reacted differently, maybe a little drag on the brake of the slow side or is it the torque converter affecting it in this way I wonder?
 

LostKiwi

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As Stwat says it's normal.
With a manual box that's in gear (any gear) with the engine stopped, the driveshaft can't move. When you turn one wheel, the other will turn in the opposite direction and at the same rotation speed as the diff gears do their magic.

In an automatic things are a little different and I'm not familiar with it, was yours in park or neutral when you did the test?
I'm a little surprised that each side reacted differently, maybe a little drag on the brake of the slow side or is it the torque converter affecting it in this way I wonder?
If the gearbox is in neutral what was observed is perfectly normal.
Open diffs such as is standard in most cars (as opposed to limited slip or torque biasing differentials) are sometimes referred to as 'lazy differenrials' in that any power input will take the easiest route out.this applies no matter where the power is input into the diff. So if you rotate one wheel and the other wheel has higher resistance to turning than the propshaft then the propshaft will turn. If the propshaft is held or has higher resistance to turning the opposite wheel will turn but in the opposite direction.

If an automatic gearbox is in gear but the engine is off there is no oil pressure in the gearbox so no clutch packs or bands can be energised hence the gearbox won't lock the propshaft but there will still be higher friction in the gearbox than if it's in neutral.
 

umblecumbuz

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And if one wheel has a higher rotational resistance than the other - ie. brake binding slightly - you should be able to detect this by comparitive feel.

Umble
 

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