Is this a really stupid question?

[piggoy]

I've been meaning to bring this up for a while now.

When my car is jacked up at the front and left in gear you can turn the front wheels by hand. Is this normal?

However if the car is left in gear on a slope with the handbrake off the car stays put as expected. Something with me doesn't add up lol!!!

 

[StevenMc29]

I thought if the car was jacked up the wheels didnt move (much).

 

[Aluco]

You can't turn both at once though can you

 

[Da]

If it's left in gear the wheel will turn forwards, but not backwards and vice versa if reverse is selected.

 

[piggoy]

You can't turn both at once though can you

Haven't tried that.

If it's left in gear the wheel will turn forwards, but not backwards and vice versa if reverse is selected.

That still doesn't make much sense to me cos if you leave the car parked on a slope in 1st with the handbrake off the car won't move cos the weight of the car won't provide enough torque at the wheels to turn the engine over? If the weight of the car cant turn the engine over I surely won't be able to with my hands :S

 

[Da]

Depends which way the car is facing with regards to the slope. If the car is facing downhill and you leave it in 1st then it will roll down the hill. Put it in reverse and it wont.

The same logic applies if you're using your hands with it up in the air. If it's in 1st gear then the wheel will be free to move forwards but not backwards.

 

[swordjo]

I always thought that 1st gear would hold a car on a downslope too.

 

[piggoy]

Depends which way the car is facing with regards to the slope. If the car is facing downhill and you leave it in 1st then it will roll down the hill. Put it in reverse and it wont.

The same logic applies if you're using your hands with it up in the air. If it's in 1st gear then the wheel will be free to move forwards but not backwards.

Haha lol. I see where you're coming from with this. I was always pretty sure the car wouldn't move in 1st whichever way it was pointing on the slope. I'm gonna have to try that tomorrow.

With regards to my car jacked up i'm pretty sure I could rotate the wheels with my hands in either direction, but i'll have to check that. If so is something broken?

 

[Jonff]

I came across the same thing when I changed a set of springs over on a 182, although while it was in gear with the wheels in the air the wheel could be turned either way, forwards or backwards. Did seem a little strange.

 

[piggoy]

I came across the same thing when I changed a set of springs over on a 182, although while it was in gear with the wheels in the air the wheel could be turned either way, forwards or backwards. Did seem a little strange.

Could it be something to do with the CV joint not functioning properly when the suspension is in such an extended position?

 

[Ol’ Tarby]

Think its down to the diff, you'll find if you got both front wheels jacked up and u rotated one clockwise, then the other would turn anti clockwise. But if you try to turn both in the same direction at the same time, then they would lock

 

[_WILL_]

Think its down to the diff, you'll find if you got both front wheels jacked up and u rotated one clockwise, then the other would turn anti clockwise. But if you try to turn both in the same direction at the same time, then they would lock

This is true, 1st will hold it on a hill, im pretty sure any gear will. I barely use my hand brake.

I can't explain why it happens, i read up about it once but i have forgotten it!

 

[Karashi]

I think a few of us need to research how a differential works! :rasp: http://en.wikipedia.org/wiki/Differential_(mechanical_device)

"If it's left in gear the wheel will turn forwards, but not backwards and vice versa if reverse is selected."

"Depends which way the car is facing with regards to the slope. If the car is facing downhill and you leave it in 1st then it will roll down the hill. Put it in reverse and it wont.

The same logic applies if you're using your hands with it up in the air. If it's in 1st gear then the wheel will be free to move forwards but not backwards."

How do YOU engine brake?

 

[piggoy]

Cheers for that. I never really considered the use of a differential in a front wheel drive car.

 

[franx]

You would have one hell of a difficult time driving if it did'nt have one in there

 

[jaysjetski]

Cheers for that. I never really considered the use of a differential in a front wheel drive car.

no offence but what difference does it make if its front wheel drive. all driving wheels have diff's it how cars go around corners without killing tyres and the car.

 

[Karashi]

You would have one hell of a difficult time driving if it did'nt have one in there

Well yes, and no... It would be laborious and tyre wear immense, but in a straight line it would be fine.

 

[piggoy]

no offence but what difference does it make if its front wheel drive. all driving wheels have diff's it how cars go around corners without killing tyres and the car.

Hence the title of this thread :rasp:

 

[ScarySquirrel]

I always thought that 1st gear would hold a car on a downslope too.

If you are facing down the hill, putting it in reverse will hold it still.

On my old Corsa the handbrake broke so I had to do this all the time until I got it fixed

 

[Alic01]

Basically you are seeing the diff in action. If you have both drive wheels up in the air and rotate one in either direction the opposite wheel will rotate in the opposite direction, this is the drive shafts rotating the cross pins of the diff but not the crown wheel which is driven by the gearbox.

If you try to rotate both wheels in the same direction the cross pins will lock up and try to rotate the gears in the box, as first gear is selected you would have to overcome the compression of the engine in order to turn both wheels, this is possible (you have to do it to set tappets on older cars) but is very difficult.

So as for hills either first or reverse will work either uphill or down but it is only the compression of the engine holding the car stationary if you dont use the brakes too.

Hope this helps