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blackwolf

Member Since: 03 Nov 2009
Location: South West England
Posts: 17527

2007 Defender 110 Puma 2.4 DCPU Stornoway Grey

agentmulder wrote:
UJs are more complex than I claim to understand but I do know that they do not transmit torque/rotational motion equally around a full rotation. ...

Strictly speaking they do if there is no deflection angle. If your propshaft was in a dead stright line there'd be no problem at all.

The issue is that as soon as a Hooke joint is driving at an angle, for a constant input speed on the flange, the shaft is driven at an irregular speed, i.e., it is accelerating and decelerating cyclicly twice per revolution. As the angle increases, the irregularity increases. This inevitably causes vibration.

If the two ends of the propshaft are coplanar, i.e., the two flanges are parallel but not aligned on the same axis, the joints on the propshaft can be aligned to cancel out the irregularity in angular velocity and drive will be smooth. If the joints are not coplanar, the joints need to be intentionally misaligned by a certain angular amount in order to minimise the vibration (the math is quite complex to determin the optimum amount of misalignment). This is achieved by careful design of the splined section of the shaft.

On the TDCi Defender the engine is nose-up in the chassis, and so the propshaft flanges cannot possibly ever be coplanar, the TDCi propshaft therefore has UJs which do not "line up".

Balvaig wrote:
Prop shafts are balanced from new and when you remove them you should mark the mating faces and refit to these marks. If they have been removed in the past and not marked , or are worn, then you can get vibration. If I remember correctly, you can refit with the mating faces rotated by 90 degrees. This can sometimes bring them back into balance and solve the vibration.

Another widespread and popular misconception, I am afraid. Propshafts are made in a propshaft factory, and balanced after assembly. They are then sent to a vehicle factory where they are randomly selected and fitted to a vehicle. They are not balanced on the vehicle. It therefore doesn't make the slightest difference how you fit the propshaft to the vehicle, and marking the flanges before removing the propshaft is utterly pointless (although it might make you feel good). The holes in the propshaft flanges on Landrovers are not equally spaced around the PCD, so that each end the propshaft can only be fitted in one of two positions, not four, and it really doesn't matter at how they are bolted up.

The propshaft assembly however was balanced at the factory, and so the alignment becomes important in the event that the propshaft itself is dismantled, for example to replace a universal joint.

The two opportunites for error are firstly not fitting the flange back in the same orientation (fitting it 180 degrees out) if replacing a UJ, which can cause balance issues and hence vibration, and secondly if dismantling the splined section of the shaft, reassembling the two parts on an incorrect alignment. This can cause balance issues and will inevitably cause a vibration due to the nature of a Hooke joint.

15th May 2017 11:12am

Defender marto

Member Since: 14 Mar 2016
Location: Wirral
Posts: 128

This is turning out to be quite an informative thread. Thanks guys.

16th May 2017 6:43am

agentmulder

Member Since: 16 Apr 2016
Location: Outer Space
Posts: 1324

Quote:
The two opportunites for error are firstly not fitting the flange back in the same orientation (fitting it 180 degrees out)

I recently took off my front and in the process marked the flanges to assist later, but when reinstalling I questioned what exactly I had achieved...

If I installed one end 180deg out (rotating TF box) what actually happens to decrease stability?

If I recall, the guiding boss/spigot (whatchamacallit) wasn't tapered either so the eventual axial alignment will be determined by the (non-zero) bolt tolerances...

Keen to learn! 👍 Solved the bowel problem, working on the consonants...

16th May 2017 6:54am

blackwolf

Member Since: 03 Nov 2009
Location: South West England
Posts: 17527

You missed out an inmportant part of my statement in your quote:

I wrote:
The two opportunites for error are firstly not fitting the flange back in the same orientation (fitting it 180 degrees out) if replacing a UJ

If you take the flange off the propshaft you could have balance issues.

If you take the propshaft off the vehicle but don't dismantle the propshaft itself, it doesn't matter how you refit it (provided you don't swap it over end-to-end, I suppose) since it was randomly fitted on initial assembly.

In your scenario it won't make the slightest difference.

16th May 2017 7:47am

agentmulder

Member Since: 16 Apr 2016
Location: Outer Space
Posts: 1324

Ahhhh, yes, my bad, I see what you're saying

Solved the bowel problem, working on the consonants...

16th May 2017 10:55pm

jst

Member Since: 14 Jan 2008
Location: Taunton
Posts: 8145

2011 Defender 110 Puma 2.4 USW Stornoway Grey

try fitting it with one UJ leading the other by one notch on the slider. Cheers

James
110 2012 XS Utility
130 2011 M57 bespoke Camper
90 2010 Hardtop
90 M57 1988 Hardtop

17th May 2017 8:09pm

Defender marto

Member Since: 14 Mar 2016
Location: Wirral
Posts: 128

I have brought a new prop shaft now and the slider part slides so much more easy than the old one which is still very still to move. The new one unlike the old one is out of phase which if I have read right mean it balanced better that way. I'll fit it this weekend and let you all know how it went.

18th May 2017 7:12am

blackwolf

Member Since: 03 Nov 2009
Location: South West England
Posts: 17527

IT won't affect the balance as such but should improve the cyclic acceleration/deceleration which you'd otherwise get and therefore reduce vibration.

18th May 2017 8:26am

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