sucksqueezebangblow
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| posted on 12/6/08 at 12:47 PM |
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How does IRS drive shaft adjust length for bump and droop?
Does any one know what the standard method is of making the drive shaft handle the change in distance in a RWD IRS set up between the diff and the
wheel hub/stub axle.
Clearly the distance is smallest when the diff and hub are level and greatest when the suspension is in full bump or droop.
How is this change in length accommodated? Does the centre of the CV joint move in and out in relation to the body of the joint? Should the drive
shaft slide through the centre of the joint? Or is some other form of joint used, such as a tripod, and if so how does that allow the length to
change?
Clive.
Better to Burnout than to Fade Away JET METAL ~ AndySparrow © 
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philtvr
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| posted on 12/6/08 at 12:51 PM |
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I thought it stays the same length as the distance doesnt change during suspension travel?
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GeorgeM
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| posted on 12/6/08 at 01:08 PM |
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does the axle not compress when you tighten the hub,??
GeorgeM
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Spyderman
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| posted on 12/6/08 at 01:19 PM |
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It is the CV joint that does the adjusting.
If you can imagine the end of the drive shaft as having a sphere-type gear on the end of it,this sphere can slide inside the tube that is the outer
end or hub-end. As the hub moves up and down it's distance from the inner pivot on driveshaft changes. The change in distance is allowed by the
sphere-type end of shaft sliding in and out of hub-end. Now to engage these two components so that they don't rotate independently there are
effective teeth, much like a gear on both sphere and inside of hub-tube. These are in constant mesh.
This is not an accurate description of the components but an overly simplified one in order to explain the principles. In actual fact on most, if not
all, CV joints there are ball bearings instead of gear teeth set into the driveshaft end. These ball bearings are trapped by large channels in the
hub-end. Thus allowing the length adjustment.
I hope this is understandable!
Terry
Spyderman
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Uryen
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| posted on 12/6/08 at 01:41 PM |
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I have also seen some shafts with slide on splines.
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mcerd1
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| posted on 12/6/08 at 01:45 PM |
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with the "bolt on" / Lobro type shafts the joints slide on splines (with copper circlips each side of each joint to limit the movement)
here's a diagram:
"push in" / Tripode joints are a bit different but do the same job:
[Edited on 12/6/08 by mcerd1]
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britishtrident
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| posted on 12/6/08 at 02:35 PM |
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The inner tripod joints accept the plunge movement.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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sucksqueezebangblow
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| posted on 12/6/08 at 02:41 PM |
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Terry, your a star.
To confirm; I fix the "spheres" to each end of the driveshaft and they slide in the outer "tubes" of the CVs? All that remains
is to fix the "spheres" on the drive shaft splines such that they take up the variation in length without over extending the joints?
The reason for the confusion is that the splines on the inboard ends of my drive shafts are longer than the splines in the centre of the
"spheres". As the splines have no circlip groves it appeared that they were intended to slide in the "spheres". But that
seemed completely wrong to me. I'm pretty sure the intention was to allow the user to set up their suspension and determine the exact position
required for the inboard "sphere" before machining circlip grooves to locate it in the correct position on the shaft.
Does that sound about right to you?
Yours, Clive.
Better to Burnout than to Fade Away JET METAL ~ AndySparrow ©
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Liam
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| posted on 12/6/08 at 04:11 PM |
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quote:
Originally posted by mcerd1
with the "bolt on" / Lobro type shafts the joints slide on splines (with copper circlips each side of each joint to limit the movement)
For the Sierra shafts the joints are not supposed to slide on the shaft splines. The circlips locate the inner part of the joint and prevent
it from moving at all. Plunge in the joint is accommodated by the ball bearings moving along channels in the inner and outer part of the joint.
So are these custom made shafts you've got, Clive? I'd suggest they are most likely designed to have Sierra-like joints fitted and have
circlip grooves machined to locate the joint as you say. I'd check with the manufacturer though to be sure. I'm only really familiar
with the Ford bits - it may be that some designs of CV indeed rely on sliding along the shaft to allow length change. Do you have the CVs?
Liam
[Edited on 12/6/08 by Liam]
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mcerd1
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| posted on 12/6/08 at 04:20 PM |
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quote:
Originally posted by Liam
For the Sierra shafts the joints are not supposed to slide on the shaft splines. The circlips locate the inner part of the joint and prevent
it from moving at all. Plunge in the joint is accommodated by the ball bearings moving along channels in the inner and outer part of the
joint.
opps - sorry about that (I'm getting mixed up with something else)
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sucksqueezebangblow
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| posted on 12/6/08 at 04:51 PM |
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Hi Liam,
Yes, they are custom shafts designed to take Ford Fiesta or GKN f3 inner joints and Sierra outer joints. I think they were originally developed by
Muffett for Fisher Fury's but are also used on the MNR VortX.
The final length of driveshaft required can vary with the amount of camber applied to the rear wheels so it is advantageous to have some flexibility
in the final position of the inner joint "sphere".
I was pretty sure I was right that the shaft splines should not be left free to slide in the "sphere" but could not find anything
definitive to say CV joints were designed to move with the driveshaft.
Better to Burnout than to Fade Away JET METAL ~ AndySparrow ©
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