Arntz IRS - radius arms required?

[750hp]

I need to replace a radius arm on the Jag IRS on my Arntz, but I recently bought a Contemporary Cobra with the same rear and it doesn't have radius arms fitted. It doesn't even have the provision for them on the chassis.

So my question; if the Contemporary has been fine for 30 years without needing them, why shouldn't I just remove them from the Arntz altogether?

Thanks.

[mickmate]

You see the break on the arm.

I have another CCX here right now that has had the same thing with a patch welded over it. Poke around on here for other examples and I think you'll find why I offer both the gussets for the arms and a Watts link for them.

[razerwire]

Went to Watts link and it shows for solid axle mustang not jag, did I do something wrong. Watts link I have seen for contempory cars was out at hub carrier and went from frame with watts link on stub on hub carrier. Dan Fodge had a fix that came from the back of car and went forward, was featured in magazine years ago. Stopped top of stock jag hub carrier from twisting and breaking parts. Also stopped drama burning out.

[mickmate]

Contemporary Cobra Watts Linkage
You can also add a radius rod going forward or back. It either has to have deflection for the radius it swings using bushings or it needs to be a triangle that gets back the the line of the pivot point like Unique uses.

[joyridin']

Here is what my car looks like. I believe there were installed by Ron Butler along with the lower differential support and the rear coilovers.

[CHANMADD]

Made these years ago.........in my gallery........the rods stop the axle tramp....back and forward movement...the watts would hold the hub from collapse if and when something beaks......
The pic above looks great although it seems a little close to the fibreglass......might hit if a real world pothole or something gets in the way......

[joyridin']

It sits pretty far away. If those rods hit the fiberglass, you have a lot bigger problems to worry about...like why your wheel just fell off!

[Tom Wells]

joyridin',

The V-shaped ones look similar to the ones Unique has been using for a long time - they seem to work fine.

Yours have Heim joints where the Unique ones (at least at the rear end) have stout rubber bushings.

Would you post a photo showing how the rods attach to the hub carriers?

Tom

[joyridin']

Relatively easy. The bracket is pretty thick...around .875". They threaded it to take the place of the rear nut, then put set screws on both sides to hold it in place.

[Tom Wells]

Thanks! Very clever!

After looking at the two methods for aligning the hub carriers it struck me that the ideal setup might be a combination of the two.

The radius rods stabilize the lower part of the hub and restrain it from moving fore and aft by more or less restricting it to up/down movement; the Watts linkage does the same for the top of the carrier.

Combining the two linkages would take twisting loads off the lower wishbone with the Watts linkage, and reduce the fore and aft movement of the lower wishbone with the radius rods.

Interesting. Wonder why Jag didn't do this? Not enough HP or torque possibly. Certainly more of a problem with Cobras, especially with slicks.

Something else for my spare time...

[mickmate]

Jag used a radius rod with a hollowed out mush mush rubber in it. You're spot on they had no where near the torque, power or traction of the hot rods and Cobras they finished up in.

[750hp]

Very interesting - thanks for the discussion. Nick, I bought Jeff Nelson's CCX so I'm lucky to already have one of your fuel tanks. The Watts Link looks great for the CCX.

To get the Arntz back together quickly I'm thinking about duplicating the current radius rod placement, but with some Grade 5 high tensile rod - 3/4" UNF.

Not sure which to use for the hub end out of
Nolathane bushed rod ends 3/4" UNF



Or Teflon lined rod ends

I can reuse the existing front bracket with some new chrome moly rod ends.

Is that on the right track?

[bill37341]

750 hp-You might try the solution I used. Simply reverse the lower wishbones left to right. This puts the original bracket for the Jag radius rod facing to the rear. (See my post to Tramsey on 6-11-12). A 3/4 inch heim joint with a 5/8 high-misalignment spacer will let you use the original 5/8 inch bolt to attach to the original location of the Jag radius rod. The spacer is necessary to let the rear-facing radius rod to swing far enough to the center of the car to line up with the center pivot point of the wishbone. Wish I knew how to post pix. Bill.

[Thor maine]

The Radius rods and the Watts link together would be the best setup for the Jag rearend.

[mickmate]

There are several good ways already shown. The lower arms need bracing forward and back and a bonus is if the hub carriers are too. The lower arms can be braced and also bridge the weld with something like this. Jaguar Rear Lower Arm Gussets Jaguar Rear Lower Arm Gussets [Jaguar Contemporary CCX] - $80.00 : Acton Custom Enterprises, Custom Metal for Cobras
I have also seen tubular braces added to these arms instead.
I have also seen urethane bushed radius rods in the fore aft position. Yet another option is to add radius rods to the front/rear or both of the lower arms so they theoretically don't change length. It's a bolt on attempt to make a tubular boxed lower arm.

I like the function of the Unique/Arntz brace but not the look of the size and the mounting hanging below the car.
I would do something to beef up the arm if I wasn't going to do anything else. Anything in addition or instead is a bonus.

[Tom Wells]

To get some ancient history here, take a look at the first photo in this thread: Broken Jag rear - WARNING!

It broke near the outer end. Still not completely sure how; it could have been the impact with the berm at Summit Point's turn 3, or...

Just an historic FYI!

BTW, the car has been rebuilt, has 30K+ miles (20K since the crash) and has been tracked at many places such as Roebling, Daytona and Sebring without incident. I do check for cracks before each session, and, yes, I never go on track without wrist restraints!

Tom

[joyridin']

I like those billet lower control arms shown on CobraRacing web site. They do not seem to be available anymore. Wonder how much they will set you back?

[Thor maine]

Originally Posted by mickmate

Jag used a radius rod with a hollowed out mush mush rubber in it. You're spot on they had no where near the torque, power or traction of the hot rods and Cobras they finished up in.

Hi Mickmate, just for giggles could you do a package deal your lower control arm gusset braces, your Watts link, and a trailing radius rod set up like the one in the photo's? And just ballpark the cost?

[mickmate]

I made the Watts as a retrofit for all stock Jag hubs. I have made a few custom top brackets for other applications. The gusset plates are also made for all stock style Jag arms. They will and have been fitted to several different applications. The radius rod I could quote a bracket for a CCX but that would really have to be made for the car it is going on. Radius rods are cheap from Day. Day Motor Sports - 3/4" STEEL RADIUS RODS - RRS-3/4
I like the idea of the reversed arms with a good premade mount point at the arm end.
I always do package discounts and try and include all hardware. I hate being all set up to get the job done and have to go to the hardware store 6 times for fasteners.