pdm
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| posted on 3/4/10 at 12:59 PM |
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Open diff question please
Hi
As I understand it an open diff allows the rear wheels to rotate at different speeds which to me suggests that the prop speed isn't necessarily
the same as wheel speed. Which in turn suggests the prop will turn even if the wheels don't ?
So in a rear wheel car, with rear wheels on the ground and handbrake on, will I be able to turn the propshaft through 180 degrees if the car is out of
gear ?
I'm ready to remove my prop on my donor at the moment and am trying to work out if I need to raise both ends of the car.
I know I've asked a couple of inane questions recently but I'm just trying to learn how things work as I go along - please bear with me
!!! 
thanks
Paul
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jacko
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| posted on 3/4/10 at 01:02 PM |
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No the prop will turn if out of gear with the wheels / hand brake on and the ground
The prop will turn at different speed to the wheels because of the gearing in the diff
[Edited on 3/4/10 by jacko]
[Edited on 3/4/10 by jacko]
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Dave Ashurst
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| posted on 3/4/10 at 01:06 PM |
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"So in a rear wheel car, with rear wheels on the ground and handbrake on, will I be able to turn the propshaft through 180 degrees if the car is
out of gear ?"
No.
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mookaloid
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| posted on 3/4/10 at 01:08 PM |
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You are nearly right - the prop does rotate at a different speed to the wheels but it is a fixed ratio - the ratio is usually around 3 or four turns
of the prop to 1 turn of the wheels.
the reason that it is called a differential is that it allows the wheels turn at different speeds to each other in order to allow the car to get round
corners.
if both wheels are locked with the hand brake you can't turn the prop.
"That thing you're thinking - it wont be that."
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Paul TigerB6
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| posted on 3/4/10 at 01:15 PM |
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You'll need to raise the rear end at least to remove the prop as the wheels need to be turned to get the prop to rotate so as to give you access
to the bolts. Keeping the handbrake operative should help as the bolts might take plenty of effort. Give them a decent soak in penetrating fluid if
you can
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pdm
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| posted on 3/4/10 at 01:23 PM |
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Ok thanks folks - I'll give them a blast with penetrating fluid now and see how I get on.
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Litemoth
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| posted on 3/4/10 at 01:26 PM |
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quote:
Originally posted by pdm
So in a rear wheel car, with rear wheels on the ground and handbrake on, will I be able to turn the propshaft through 180 degrees if the car is out of
gear ?
No. There is a mechanically 'fixed' gearing between the input (prop) side of the diff and the driveshafts (as a pair). The output
revolutions are 'shared' in different proportions between the two driveshafts but will 'add up to' the revolutions inputted by
the prop (in a 4:1 ish ratio because of the gearing).
When driven, the car wouldn't move if the prop just freely spun at the diff end 
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loggyboy
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| posted on 3/4/10 at 03:05 PM |
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http://www.youtube.com/watch?v=yYAw79386WI
Skip to 2min.
[Edited on 3/4/10 by loggyboy]
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pdm
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| posted on 3/4/10 at 06:45 PM |
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That's an excellent explanation video loggyboy - thanks for the link.
Thanks as well to everyone who replied - I'm clear on what I need to do now.
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Litemoth
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| posted on 3/4/10 at 07:00 PM |
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Really good explanation that!!
It's amazing how little the engineering has developed in 73 years!!
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