Thread: Castor Correction - swivels or radius arms

Originally Posted by JEEPEYTR

So are all of our lifted 90’s now shorter wheelbased than a Series? I probably just got banned for this long winded reply too, didn’t I?

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~Scott T.
'95 NAS D-90 ST (JEEPETR)
"If you're not living on the edge, you're taking up too much space!"
http://www.putfile.com/lrnad90

Maybe....but 88" is a good thing in my book.

Originally Posted by Defender200Tdi

As I understand it, there are two bends usually made in the radius arm, making it into a kind of stretched Z shape. One bend to correct the bush alignment at the chassis end, and the other to correct the castor. The second bend is the one that tips the diff nose back down correcting castor, but putting the strain on the uni joints.

I wonder of doing the first bend to get the bush alignment back, but not doing the second bend to correct castor, thus leaving the diff nose pointed up at the transfer box, would alleviate some of the chances of the uni joints complaining? Rotating the swivels could then fix the castor.

Getting the length back in the radius arms seems to be the tricky bit. Adding washers on the front bush can only go so far before the bushes are over compressed, and you'll only evr get half of the thickness of the washers you add after both bushes compress and equalise. I suppose if the arm comes out only 1mm shorter, then a 2mm washer should do it.

Paul

Paul thats the best idea ive herd so far ant some time tomorw il mark it out on a flat plate and play with sum numbers as like jeepeytr said wilt the geometry of it it dont sound rite with the lengths so the only way to do it and to get the answers is to lay it out and see what i come up with il have a go and il take sum pics and get back to you guys over the weekend some time

Cheers

Chris

Originally Posted by JEEPEYTR

Okay, I hate to sound like the idiot from the States here, but.. We lift a truck, lets say 3”. This forces the axle down away from the frame. Since the radius arms that are locating the axle haven’t changed, pushing the axle down rotates it forward as well (Rear pinion rotated upward). I’m sure we all agree on this, correct? At the same time, we have pulled the axle’s position rearward slightly, just as a matter of geometry, since the axle articulates downward in an arc (think Isosceles triangle here).

I hated algebra, but A squared plus B squared equals C squared, where ”A” is the distance from the radius arm mount on the frame to the point on along the frame where the center point of the lower spring seat is directly below it, “B” is the distance from this imaginary line directly down to the spring seat, and “C” is the distance from the radius arm mount on the frame to the axle along the radius arm’s path. Still making sense?

If we use the number 48” (rough guess of the actual distance) for “A” and 14” for “B” to represent stock (approximately the distance between the spring seats with a stock spring), this calculation gives us 50” for leg “C”, or the distance from radius arm mount to axle center, along the line created by the radius arm itself.

If we kick the numbers around a little, continuing to use 50” for “C” and using 17” for “B” (representing 3” lift), we can solve for the distance “A” which comes out to 47.02”. This suggests simply lifting 3” without changing anything else moves the axle back almost a full inch (not to mention that lifting the rear has drawn the rear axle forward in a similar matter, since it also articulates in an arc). Looks like we are now all series coiler drivers with 88” wheelbases, LOL!

But back to the radius arms. If we bend a standard length of metal that is relatively straight and 50” in length, its overall length is going to become less, which would suggest pulling the axle even further rearward. I guess after all this my question to HSV is, 2 mm seems hard to believe to me, given the considerable nature of the bends. I would think more like 2-3 cm or about an inch would be more likely, was this measurement actually taken “on the bench” before and after the arms where bent? Cause if this is the case, than the proof is in the numbers, and my head hurts for nothing.. Sorry about all the non metric measurements, by the way.

So are all of our lifted 90’s now shorter wheelbased than a Series? I probably just got banned for this long winded reply too, didn’t I?

--------------------------
~Scott T.
'95 NAS D-90 ST (JEEPETR)
'96 Disco SD 5-speed (sold)
"If you're not living on the edge, you're taking up too much space!"
http://www.putfile.com/lrnad90

I thought similar prior to doing this.

But when I lay the modded arm next to Std arm they are no different in lth 1-2 mm only.

this is caused by the arm stretching at the bend more so than shrinking. It works when done hot.

Michael.

Originally Posted by lokka

Paul thats the best idea ive herd so far ant some time tomorw il mark it out on a flat plate and play with sum numbers as like jeepeytr said wilt the geometry of it it dont sound rite with the lengths so the only way to do it and to get the answers is to lay it out and see what i come up with il have a go and il take sum pics and get back to you guys over the weekend some time

Cheers

Chris

This is a good option but you will need a double cardan joint.




Regards
Michael.

The best option is to crank arm at chassy end to realign the arm to bush.

Crank arm if required at diff end to align pinion correctly to out put on T/case.

Then fit double cardan shaft

Then rotate swivels to correct castor.

Michael.

I believe it is this plane that the included angle is critical.
StdDriveshaftjpeg.jpg

A double cardan joint is basically 2 universal joints coupled in close proximity.
A constant velocity joint is different again.

Originally Posted by oldzook

To avoid vibration the diff pinion & the Xfer case output shaft need to be as close as possible to parallel, within a tolerance of 3deg comes to mind.

Yes, I agree. But I suspect on the standard setup for a Landrover, they aren't even parallel to start with. Wasn't this the reason Landrover came up with the out of phase bodge for the uni joints at the front? In any case, lifting the suspension probably just makes a dodgey arrangement even worse.

Paul

Yep your spot on. That's all I was pointing out, is that by not putting in the second bend it would be encouraging the vibration issue. They are on their limit from bog standard and any further modifications will only exacerbate that.
Of course there are trade offs to any design.
Whenever I stop throwing coin at my house [insert exasperated sigh] I plan to get serious with the LR. However the Disco being such a "nice car" to drive I want to make sure I don't accidently go overkill and make it a pig to drive to and from interesting places. Have made some poor engineering descisions in the past with cars/bikes and learnt my lesson.
Of course a dedicated weekend warrior is going to have different priorities too, so what's acceptable nuances to one person will drive another bat crazy.