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Handedness of Replacement Halfshafts?
#1
Hi

I recently mentioned to a friend that I have a spare halfshaft for the Ruby and he asked if I knew which side it was from.  He then suggested there might be an increased chance of early failure if used on the opposite side from its original position.  Has anyone heard this before, and is there any truth in it, I wonder?

Colin
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#2
If that was the case, all half shafts should snap when you reverse ? If it were supposed that the keyway would fail, it should not as no load should be on it when the hub is lapped to the shaft and tightened correctly.
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#3
I am no engineer so I don’t know the answer but could it make a difference if the half shaft was used on one side for years then after a strip down re assembled on the other side.

John Mason
Would you believe it "Her who must be obeyed" refers to my Ruby as the toy.

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#4
Changing sides should not affect the half shaft.
If it was on the limit of strength it might, but I'm sure the A7 is plenty strong enough.
A friend had a Land Rover Series 2 12 seater safari. These weigh nearly 2 tons and the original Rover shafts were near their stress limit. Half shafts and diffs failed fairly regularly. He found that by reversing as little as possible they lasted much longer. He had plenty of room at the house so he could turn without reversing.
Fitting Salisbury axles was the permanent fix.
Jim
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#5
I think the worry - and it perhaps arose with other vehicles such as Land Rovers and MGs? - is reduced high-cycle fatigue life (so not from reversing) - but Seven halfshafts tend to fail from damage after the hub comes loose rather than from direct driving loads?
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#6
Austin Seven halfshafts tend to fail from cracks which originate at the keyway, which are entirely avoidable if the taper is lapped and the nut done up tight. And which has nothing to do with 'handing'. That of course and ridiculous abuse...

I'd venture that any used gear mated with an unfamiliar part is not going to run ideally, at least till some re-bedding has occurred, but I don't think this is a big enough worry to stop you using second hand shafts, and again hasn't much to do with handing.
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#7
That's good - so I don't have to buy another one (or two or more)? Heavy, aren't they?
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#8
For other makes which fail at splines it is considered very poor practice to reverse a half shaft. Often leads to early failure. Occassional early overstrains considerable increase resitance to fatigue in that direction. But when crack tested Seven axles often reveal a crack at the corner of the keyway on the drive side. Often seem to progress initially and very slowly around the semi circle cutout rather than across the axle. So probably better to fit reversed! (And as previous it is important that full or at least good contact is made inboard of the key so the key section of the axle transmits minimum torque and bending)
I would not worry about meshing of the gears. On other makes with mitre gears these get into a parlous state with no effct other than harmless increased backlash.
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