Castor correction

[dollythelw]

so is it a Burgess double UJ prop then?

[white90]

it is a L/R D2 prop but will be modified by Burgess

[dollythelw]

thought so they do all mine, good lads and seriously quick

[Steve Hiatt]

Last one I had done the UJ was fitted the wrong way round making it impossible to grease. When I removed it to change it round one and a half needles were missing. I did this before fitting it to the vehicle and on a clean bench. Didn't get any joy on the phone and ended up buying another joint at £20 plus for two needles.

Everything else has been OK.

[Bush65]

Jez, if what John (Bush65) says is true, they are already 45 degrees out of phase - which I can just about resolve in my head - to compensate for the angles on the two UJ's not being the same.

By increasing or decreasing this phase difference, it might compensate for a bigger difference? Seem reasonable?

Si

I have mentioned this several times on this forum and there have always been doubters, which makes me wonder how many of the doubters have there eyes open when they are under rovers, or if they ever get under them at all. Of course the other more obvious alternative is that my explanations are unclear - it is a great pity that posting pics is such a pain on this forum.

Have a look at the 1st pic that Tony posted above. Blind Freddy can see how the yokes at both ends of the driveshaft are out of phase. This is standard on coil sprung rovers (except those with double cardan joints).

The problem with double cardan joints is that they can't operate at angles as large as a good wide yoke u-joint.

I have a disco II driveshaft in the front of my rangie and it limits the articulation. After the tray back mods it will get a driveshaft with a clearanced toyota hi-lux double cardan joint.

[MudAllOverIt]

Have a look at the 1st pic that Tony posted above. Blind Freddy can see how the yokes at both ends of the driveshaft are out of phase. This is standard on coil sprung rovers (except those with double cardan joints).

I've been reading this thread and wondering just what the hell all this talk of out of phase yolks was all about but, er, now that it's been pointed out I'm starting to wonder how the hell I never noticed before

[Turbocharger]

Mr Bush is right. The last time we discussed this (sigh) I played with some maths to work out if he spake the truth, and he does.

The reason for it is (image stolen from the old thread, wherever it is):

When the UJ angles are the same (flanges parallel), the prop accelerates and decelerates as it rotates but the speed of the driven diff is (nearly) constant because one UJ cancels the other, just as we were taught in school. Here, the output shows a slight vibration because I only calculated every 5 degrees or similar. If I calculated every 0.000001 degree the line would be flat.

When the angles are not the same, (ie 20degrees at the gearbox and 0degrees at the axle, a la standard Ninety) you get a nasty first-order speed change at the diff end as the diff accelerates and decelerates twice every revolution, just as the prop does normally - there's effectively no second UJ to cancel this speed change.

You can change the prop phase to superimpose a second-order effect onto the (first order) prop rotation speed change (so your average speed stays the same, but the purple wiggles on the graph above get bigger). This is exactly what LR did at the factory, you get less amplitude at twice the frequency, which are small enough to become unnoticeable on factory models. However, if you lift the vehicle the peaks of these vibrations are now big enough to be felt, and you splash out on a funky double-UJ prop before it shakes your teeth out.

For bonus points (I'm not giving this one away because it gave me brainache to figure it out and I deserve to feel smug for a bit) why is the average of the purple line visually greater than the average of the blue line? ie the diff pinion is apparently rotating faster than the prop?!?!? I will buy a beer at Billing for the chap (or lady) who can figure it out first.

[white90]

I have mentioned this several times on this forum and there have always been doubters, which makes me wonder how many of the doubters have there eyes open when they are under rovers, or if they ever get under them at all. Of course the other more obvious alternative is that my explanations are unclear - it is a great pity that posting pics is such a pain on this forum.

Have a look at the 1st pic that Tony posted above. Blind Freddy can see how the yokes at both ends of the driveshaft are out of phase. This is standard on coil sprung rovers (except those with double cardan joints).

The problem with double cardan joints is that they can't operate at angles as large as a good wide yoke u-joint.

I have a disco II driveshaft in the front of my rangie and it limits the articulation. After the tray back mods it will get a driveshaft with a clearanced toyota hi-lux double cardan joint.

yes I can see they are out of phase and no altering of that made any difference.

the prop was brand new and was supplied like that.

all TD5 defenders have the same set up.

[MarkieB]

For bonus points (I'm not giving this one away because it gave me brainache to figure it out and I deserve to feel smug for a bit) why is the average of the purple line visually greater than the average of the blue line? ie the diff pinion is apparently rotating faster than the prop?!?!? I will buy a beer at Billing for the chap (or lady) who can figure it out first.

My 'starter for 10' guess is that it's to do with the 'time' axis being in angle of rotation rather than time; so giving a misleading impression of the amount of time that the components are moving more slowly

I'll save the price of the Beer for a future occasion

[Turbocharger]

My 'starter for 10' guess is that it's to do with the 'time' axis being in angle of rotation rather than time

Err... yes, that's it. First answer too... Beer debt duly noted down. There are more techy people on here than I thought