I am taking the opposite approach  I am going to make my trailing arms solidly mounted to my wish bones (will probably make a tubular one piece unit later)  and then mount my single shock, roughly in the middle of the front trailing arm pivot and the rear LAC pivot this will center the shock  and help eliminate twisting.

The image of the cobra rear set up has to be the best looking solution to the LCA  problem with out redesigning the whole damn concept . The integrated "x" bracing and widened coil over mounts should provide some needed improvement .  The further apart the coil overs are mounted on the LCA, The greater their ability to act as a torque couple and resist rotation while supporting the weight .   Who ever did this had a good idea what forces were involved and came up with a clean design with few compromises.

I think it would help.  are you planning to just run one coilover per side??? I am approaching the same problem by putting the coil over in the front and then solidly mounting the trailing arm to the LCA and using it to effectively make the LCA a three pivot unit.  Some day I may make a tubular unit and then it would look something like the arm on the left in this pic

so tyrellracing is your IRS in the car???? I know when you were posting before it was still in the works.  Also how did your custom vented rotor project come out??

Sorry guys, I should have been more clear in my post. " This tubing would be added on both sides." meant on both sides of the one control arm, four times in total. And yes, I'll be using 2 shocks per side, four in total. (The internet is like that. You always have to be aware of how your statement might not be taken in the intended way).

I liked the theory of the widening of the two shocks on one LCA,  increasing the "torque couple" effect. That's a good thing.

Also, on the later Jag IRS installations,  I noticed the factory supplied a small bracket to link the outer fulcum point to the lower shock mount. This was a bolt on afair, although it seemed to me, a bracket from the inner fulcrum to the lower shock mount would have been more benificial.

This modification I've layed out here is of course entirely contained to the LCA. If I could explain the plan of my IRS installation in a bit more detail, I said I was going to use a "  pair of differential support rods at the front and the back of the differential ". This would be a pair of 1" rods with a clevis at one end a nylotron bushing at the other end going,  from the front  inner pivot point of the LCA, angling forward and outward by 60 degrees. Theoretically, just those the two rods would be sufficient to resist the forward and aft, side to side forces of the differential. However if a little bit is good, alot must be better. Therefore, I want to add two more similar rods  from the rear inner pivot point of the LCA, angling only outward by 60 degrees. All these rods would be attached to the "tie brackets" that tie the two differential side brackets or trunion mounts together, one front, one back and of course the car chassis.  That's alot of hardware but I think you want to make sure the differential is in there securly. You need to put something in there to take the place of the original Jag cage.

And again, the Watts Linkage will be on top of the hub.

Getting back to "weakest part of the control arm" that inner bend, I don't see any other way to improving it other than replacing the entire LCA which is not in my cards at this point.

Ken

Ralphy,
You got it! And then I'll add something similiar at the front.

Looking at that photo, it makes me think about a conversation I had with Ron White from Snow White Ltd., Street Rod Parts and Mfg. He suggests the axle should be angled down at 2 degrees towards the hub on a Jag IRS installation. I asked him why and his answer was that it just works best, gives the best ride. He's been doing these installs for 35 years and this is what he's found. This 2 degrees amounts to a 1/2" difference between the differential and the axle cenre lines. Have a look at their products:
http://www.snowwhiteltd.com/products.htm

He states the 2 degree fact in the instuctions of his kits. Here's the 40 Ford instructions as an example, (you'll find the sentence towards the end in the notes):
http://www.snowwhiteltd.com/instructions/40fordcross.pdf

However, in this article, you'll see they illustrated theJag  IRS with the axles level:
http://www.jagweb.com/aj6eng/suspension.php

Ken

Ralphy wrote:

Factory I believe they want the half-shafts straight. Never below center!

NO NO NO 

On a factory jag setup they want the LCA parallel with the ground and in line with each other.  that is where you put it when aligning the car AND is how every Jag I have ever stuck my head under looks... unless the springs are sagging 

Last edited by Daze (1/13/2012 10:15 am)

" Half shaft angle should be 2-3* down from center at ride height, at full curb weight.""
Russ T Nut
"I don't know where you came up with the 2-3 degree angle :confused:. The top dogbone should be level at ride height."
Chevynut
the 2-3* came from a pickup installation on a Fo*d, and I assumed it was to allow for needle bearing rotation.
Russ T Nut
http://www.trifive.com/forums/archive/index.php/t-11064.html
**********************************************************************************************************************************

IRS Thunderbird half shaft geometry?

"There are two schools of thought about the correct setup. One being that the halfshaft should be level at max acceleration or Two that they need some angle to keeping from brinelling the race due to the high loads under max acceleration. I feel that it best to just split the max angularity that the unit will see in service. I try to put in about 1>2 degrees at steady state to allow the unit to have some plunge which increases the area that the bearings see on the race."
__________________
Best regards,

Richard Hudgins

JBL MOTORSPORTS
http://www.clubcobra.com/forums/shop-talk/70549-irs-thunderbird-half-shaft-geometry.html
************************************************************************************************************************
pringles

"I was at Home Depot today and when I came out a C4 was parked behind me. I had a look under the car but it was difficult because it's so low and I didn't want to get to close to it and touch it. I am pretty sure I noticed that the half shafts are angled slightly down and the trailing links slightly up at rest. "
http://www.pro-touring.com/archive/index.php/t-74310.html

http://www.lvvta.org.nz/documents/infosheets/LVVTA_Info_08-2011_Jaguar_IRS.pdf

Last edited by Ralphy (1/13/2012 1:39 pm)

Dog bone, wish bone....everybody's got a bone to pick!

Daze wrote:

I am not talking about the half shafts.  I am talking about the LCA or wish bone.  On a Jag the wish bone NOT THE HALF SHAFT needs to be parallel with road at normal ride height Just the way it is set in the picture posted.  On the shop manual they want camber at 0º at normal ride height and they want the LCAs parallel with the road and in line with each other at normal ride height.

Just currious - I suppose that is because at ride height - the shocks are at "mid-point""- between full bounce/jounce?  Thereby giving max travel up/down on the suspension.

Cheers - Jim

here is proof that the pic is both accurate and the LCAs still need to be parallel with the road.  if you look at the tires they are leaning in at the top and so the camber is negative.  If in the pic the camber were at 0º the LCAs would probably be parallel with the road.  I am sure that pic was a snapshot from an animation and it was stopped some where in its range of motion but not at 0º camber

My last comment was in reply to this.

"yes it is and I have been trying to tell you that for months    more than once you have made a comment to the effect of ' the hot rod guys make the LCA parallel to the road for looks but that not how it should be' "

I did some further looking and I am a dork it was JEM not you.  It was probably someone else before him and some one else befor that as I know I have said it many times.  seams to be a common misconception when installing a Jag unit that the LCAs are not to be parallel with the ground.  I new I had preached this sermon before, and I thought it was to you, but I was wrong.  Sorry my bad 

Last edited by Daze (1/13/2012 4:59 pm)

Ralphy wrote:

I'm no doubting you, conversation is more visual than we think.

Did you see the post above the one you just made, it was all me I am a dork   Also did you see I responded to your caster question??

Ralphy wrote:

Then the other point I was making about narrowing I think is true. When you narrow an IRS you speed the camber curve. Imagine a half shaft 2" long and move it up or down 2". Then imagine a half shaft 10 feet long and move it up or down. The 2" length would camber all over, the 10 foot would camber very little. So if you were to narrow an IRS the first 1/2" has the least movement. By making  it move through both sides of the least motion, you will slow the curve. Also lowering the inner pivot of the dogbone and or moving it out will also slow the curve. So if you narrowed even a Jag this would slow the camber.

You are correct, it does reduce the curve by narrowing the parts.  here are some numbers Joe ran for me comparing my  narrowed IRS to a stock XJ6 unit.  this is the difference 2" makes