Jaguar IRS Trailing Arms
 

I am in the final stage of a Jaguar IRS conversion and have been doing some reading about trailing arms. I have read many articles that say they are not needed when the diff is solid mounted.

If they are used, the triangulation needs to be spot, so I am wondering if I really need them. When I shortened the LCR, I welded gussets to strengthen them.

How are your Cobras setup with Jaguar IRS?

When our local Cobra group went on a high speed driving course at Killarney race track in Cape Town in the mid 90's the instructor (A national champion racer) commented that the only car that was really planted on the track and gave him confidence to push the limits was the one with proper trailing arms. All the cars he drove were Jag based at the time. Some had the jag trailing arms some not but the one he liked had properly aligned trailing arms.

All the cars had solid mount diffs.

ERAs have trailing arms but they are dual purpose. The differential is mounted in a cage that is secured at the top by bolts to the frame that act as pivot points. The trailing arms are adjustable and allow tuning of the placement of the wheels fore and aft in the wheel wells and some slight adjustment in differential pinion angle (although I've not read of the adjustment being used for this). Even through the cage pivots the trailing arms still act as locating arms to the frame to positively locate the hubs fore and aft due to road stresses and impacts. Very slick arrangement and I hope I'm not mis-describing Bob's (ERA) engineering intentions.

The lower Jag control arms are pretty rigidly mounted to the differential but I would think there would be some deflection from wheel impacts and loads. If you fabricate and install trailing arms for a fixed differential situation, IMO they should be adjustable in length so you can fine tune them to the differential/control arms position.

Unless the front end pivot of the trailing arm is in-line with the lower control arm pivot axis, you need some compliance somewhere. ERA accomplishes that by rubber mounts at the top of the subframe (that contains the rear suspension main assembly).

So the body mounted side of the trailing arm has to be in line with where the LCRs mount to the Axle?

I actually have trailing arms installed, one end has polyurethane bushes and the other has a hiem joint.

[IMG]http://i612.photobucket.com/albums/t...b/IMG_2369.jpg[/IMG]

It may be worth looking at Snow White Hot Rod Shop - they have developed and sold Jag IRS mounting kits for uncaged kittys for decades. That having been said, keeping the original Jaguar cage and factory setup will give you the ride and handlng that Bob Knight originally designed in 1957. This used stamped steel trailing arms/radius rods with large diameter rubber bushings and bolts into the unibody. These had safety straps fitted - an item often left off on transplanted installation - but they were there for a reason and should be used if an OEM setup is desired.

ERA offers an outboard brake rear end option but as an fyi, the mid 1993 to end of production in mid 1996 XJS models had outboard brakes. This makes servicing a breeze. The diff ratio was 3.54 on all of these, with a low bias posi. The differential housing was modified to allow the park brake cables to be mounted on special brackets attached to the housing. A very few of thes outboard braked IRS had ventilated rotors. The IRS was 61-3/4" hub to hub so you would have to narrow the lower control arms and half shafts. You can also convert an inboard IRS by using the hub assemblies and halfshafts (narrowed of course) from a Jag XK 8 up to 2003 vintage, but you have to make your own parking brake mounting solution as the inboard diff housing does not have any bosses for this. I got some XK8 hubs, brakes and halfshafts from a Jag only wrecking yard.

LCR?? The inner axis of the lower control arm should ideally project forward to the front mount of the trailing arm.

LCR (Lower Control ARM)

"The inner axis of the lower control arm should ideally project forward to the front mount of the trailing arm"

Thanks for this, that how I understood previous comments.

I am actually only a few inches out, I can build some brackets that lower the trailing arms so the body pivot side is at the same level as the LCR inner pivot.

[ame="https://www.youtube.com/watch?v=asGKiXUz_zo&feature=youtu.be"]https://www.youtube.com/watch?v=asGKiXUz_zo&feature=youtu.be[/ame]

http://www.clubcobra.com/photopost/d...us_arm_004.jpg

These work great

Yea, thought about a watts linkage, that's allot of work. Here is another Watts option, this would be easier to fabricate.

http://i612.photobucket.com/albums/t...b/101_0137.jpg

Made adjustment to the trailing arm mounts, I welded on two tabs that allowed me to lower the fulcrum point to be at the same height as the LCR inner fulcrum point.

http://i612.photobucket.com/albums/t...b/IMG_2385.jpg

The "watts "system made by Mickmate is the way to go, plus add a "trailing radius rod system like the one that came from Unique Motor cars and you will have the best the Jaguar rear suspension you can get.