Vehicle & Technical > Series Land Rovers

high angle prop

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karloss:
Catted ? What's that then?

muddyweb:

--- Quote from: "karloss" ---Catted ? What's that then?
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Fitted with Catalytic converters.

The V8 Auto Disco has a very strange solid bar front propshaft due to the fact that the cats are in the way of a normal type.

karloss:
Ah.
Any pic's Neil?

Range Rover Blues:

--- Quote from: "muddyweb" ---
--- Quote from: "Range Rover Blues" ---usefull for coil-sprung vehicles as a suspension lift causes the front axle to roll forewards (also changing the castor) so that the UJ angles do not match.  Castor correcting arms then make matters worse.
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um... you sure about that ?


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Very sure, yes.


--- Quote from: "muddyweb" ---
The castor correction brings the diff nose back down and increases the drive angle of the bottom UJ.   In order for the prop to work properly, the drive flanges should be parallel, and the castor correction gets the diff flange closer to this state.   When you lift a vehicle, as you mention, the diff nose turns upwards making the flange move further away from parallel.

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Yes, as you lift the car the diff nose turns upwards but the bottom uj angle remains almost unchanged because the prop and radius arms swing down together, the radius arms mount almost in line with the top UJ so that has to do all the work so to speak and it's angle is increased.  This gives the imbalance that leads to the pulsing we are all familiar with.


--- Quote from: "muddyweb" ---
What castor correction arms will do is effectively extend the distance between the flanges, which can cause issues with additional strain on the UJs if the slip joint is near its limit.

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Agreed, in fact the QT arms are slightly longer to re-establish the wheelbase after lifting the car, which has the effect of shortening it.



--- Quote from: "muddyweb" ---
For a double-cardon prop to work well, the lower UJ needs to be within a couple of degrees of 'straight'.. and in this case, the castor correction arms can be a disadvantage.


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If you mean the TD5 style prop with the Cardan(double UJ) prop then yes, the single UJ needs to be as near to straight as possible to let the top UJ do all the work.  Fortunatley a Cardan has a higher angle anyway but not twice that of a UJ.

You've already said the drive flanges should be parallel for a normal prop to work correctly.  This isn't strictly true, both UJ angle need to be identical and this is I think where people get confused.

In a traditional car the engine/gearbox slope downwards to keep the sump above the front axle and the gearbox under the floor.  This has the advantage of making the ooutput shaft of the gearbox point directly at the rear diff pinion shaft, so making the rear propshaft almost straight.  this is also true of most LR products, the rear prop UJs are almost straight and as you say the flanges are parallel.

Imagine now the front end of a Range Rover (the original coiler after all) and you have a shorter propshaft with the added disadvantage that the front output flange is pointing at the sky, not the road.  To keep the flanges parallel would mean the nose of the diff pointing at the floor (parallel to the rear axle flange) and the UJ angles would be horrendous.

To cure this LR engineers did a clever thing, they rolled the diff within the axle to point the nose well upwards, having 2 benifits.  Firstly the upper UJ angle was reduced, secondly they were able to match the UJ angles in magnitude but not direction.  So if the top UJ turns downwards 10 degrees (I havn't measured it) the bottom UJ also turns DOWN 10 degrees (prop to axle) so effectively the front prop is one huge Cardan joint which works by sharing the drive anfle between two UJs.

So when you come to add castor correction arms you roll the front axle backwards, REDUCING the bottom UJ angle to almost zero and increasing the top UJ angle ever so slightly because the flange sits lower to the floor.  this causes the pulsing much more, because the higher angle at the top UJ (gearbox) creates more pulsing plus the bottom UJ no longer 'undoes' the effect because it is now straight.

Everybody clear on that? :?

muddyweb:

--- Quote from: "Range Rover Blues" ---You've already said the drive flanges should be parallel for a normal prop to work correctly.  This isn't strictly true, both UJ angle need to be identical and this is I think where people get confused.
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Yeah... don't know why I said that... it is, as you correctly point out, utter nonsense !   I think it came from a diagram I was drawing for someone the other day where I drew the flanges parallel to make showing the angles easier  :roll:

Brain getting carried away with itself again.

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