Broken Jag rear - WARNING!

[Tom Wells]

Hi All,

I've posted these pics in my gallery and will try to make them appear here:

[Tom Wells]

Here's the second image:

[Tom Wells]

Here's the closeup:

[mrmustang]

Tom,

Have we figured out hoiw this occured yet??? Looks like metal fatigue........Also, from the rippled edges, it looks like it has been going on for a long time, and was never noticed...................


Bill S.

[Tom Wells]

Now for the warning and some questions:

WARNING: This break cost me a pulverized wrist on turn 3 at Summit Point. The best we can figure, when the wishbone broke, the driver's side rear tire got jammed forward into the wheel well and froze. The car slid off the track, into a berm and flipped over. My instructor was miraculously unhurt - except for a sore knee for a couple of days - and I received no other injuries. Alas, my second surgery is scheduled for tomorrow

Questions:

1) Why did this break? Is 412 RWHP too much for this wishbone? It was a stock, unmodified 3.8S unit.

2) How can I prevent this when the car is repaired? Is there a better/stronger wishbone available?

Oh, and do yourself a favor - get some arm restraints for your track time!

Tom

[Woodz428]

From the pics it looks as if it may have had corrosion working on the inside to create the failure. Isn't that a flake of rust on the inner surface of the last pic?

[mrmustang]

Tom,

These are what you need:

http://www.cobraracing.com/ProductsP...tml#XK2001anch


Bill S.

[Double Venom]

Tom,
My,my. Good luck today with the "modifications" and customizing!

I sure hope some professional Jag rear end type guys jump in here. I have seen three failures like this on the Jag rear ends;
Run N Gun-weld let go
Dhris Knueven - Blue and White Unique broke a lower arm at last years Fling.
And now yours.

I, in a very non-professional Jag expert, have to agree with Bill. Looks like fatigue to me?

Can they be built with stronger tubes? Maybe a "double-wall" prior to welding the caps on?

I think Bob (Putman) makes his own tubes?

DV II's use a single wishbone setup, totally custom made for our horse power and torque, but I'd still sleep better with a "Double Wishbone" set up.

DV..Here's to a very quick recovery fella!

EDIT..PS, just went back and read all of the original thread. Some good stuff there From David!

[Tom Wells]

Hi DV,

Interesting...

Is there someplace I can find out more detail about the other two failures at the Run 'n Gun & Knueven? Photos etc?

I'd also like to see what corrective measures thoes two guys took!

Thanks!

Tom

[rdorman]

The jag rear is strong but when it fails, it usually is not pretty.

You might also try Concours West Industries. They have a tubular lower a-arm as well as the billet one. I would think the tubular one would be considerably less expensive than the billet. They also have a BUNCH of other cool stuff for Jag suspension.

Jag rear ends suffer from torque steer (toe control), camber control (spider gear slop). The toe issue is usually a result of the bushing complience and any slop in the side spider gears in the diff. will result in loss of camber control.

I have seen where virtually every part in the rear has been created with an uprated, newly designed peice. If I had my way, it would get a new tubular lower arm, a carrier that would accept and upper arm, a tubular upper arm and an outer CV half shaft arrangement that will accept the plunge. But them it wouldn't be a Jag rear now would it!

Minimum would be the lower arm (with trailing arm) that would be fully adjustable and a modified hub for watts linkage. Seems to me some one could do that for a reasonable amount. Being a little creative you could even make one that will adjust camber. Plus the roll center needs lowered (easy to do), seems to me it is over four inches above the ground.

So who wants to be my test bed? How about a reasonable line of cobra related performance suspension pieces? If I only had more time!

DV, seems to me that Chris broke and upright (hub carrier) where the pin runs through the upright from the a-arm. But, I could be wrong!

Rick

[rdorman]

Chris is on here as excessive1.
Rick

[Eljaro]

When Contemporary was still in bussines they replaced free of charge the two control arms for the Jag rear end. I still have them, completely new in a box. They were reinforced and it seem that Burtis was aware of these problems many years ago, thus the free replacement.
I never got to put those control arms into my Cobra, but prefered to get a complete rear suspension from AMP , which works very well, with a bulletproof billet aluminum control arm. Check out http://www.cobraracing.com/index.html

[ToyCollector]

Originally posted by Double Venom

EDIT..PS, just went back and read all of the original thread. Some good stuff there From David! [/b]

DV, where is this original thread you mention?

Tom, glad you and instructor are OK. Surprised they let you run without the straps. Hope car gets fixed to your satisfaction.

[Back in Black]

Even in perfect shape.. it looks to me like simple metal fatigue at the weakest point.. the shape change from straight tube to the hub area....

For those who may have not seen it, this is the only IRS I would consider for these high-powered cars we love:
http://www.geocities.com/~concourswest/

9 inch Ford drop out center IRS unit is the one I would use....

[Steve R]

Tom,
I'm glad to see you are OK. The Jag setup has always given me the creeps. I keep thinking about what would happen if a half shaft broke under load, at speed. I guess I kind got my answer.
Now for the related question: would you please give us details on how you set up your seat belts? There has been a lot of controversy about this subject. Here we all have some real world results to ponder. Please be specific as possible.
Thanks!
Steven

[Steve R]

Guys,
Take a look at a Shamrock Cobra's rear. As I remember it, they weld a tubing sleeve over that area. I wondered why When I saw It. I guess I now have the answer.
Steven

[K.Wilson]

Tom,
It is difficult to tell what the exact failure mode is by looking at your photographs. To be sure you would have to do a micro-section of the the weld (a small piece of the weld filler metal, the weld effected zone of the tube, and the tube would have to be encapsulated in epoxy then polished and viewed under a 20x microscope).
However, from your photos it really looks like there was very little weld penetration into the tube material (the filler metal did not melt and mix with the tube material as a result of a low temperature weld,or the duration "dwell time" of the weld was to short to get proper penetration).
Usually when metals work harden you see a lot of exposed grain structure that has been smeared but in this case it is not obvious by the photos.
Hope you feel better soon.
Keith

[coyled]

That is pretty scary. The only thing I can add other than stronger parts (pretty obvious) is that we all need to check and recheck all nuts, bolts, welds, and for any cracks. The break does not look completely clean to me, maybe there was a sign of it before hand or maybe not with all of the paint on the tube. I am glad to here that everyone is relatively ok. scott

[Tom T.]

Steve,

It doesn't appear that the halfshaft failed in addition to the lower control arm failure, based on what I see in the pictures. A properly built Jag diff can take a whole lot of h.p.--it's essentially the same Salisbury unit that was used on the original Cobras, I think. But you have to use upgraded halfshafts and control arms. Watts improves things further by providing some protection from wheel flop over in the event a halfshaft fails, I believe. As previously noted, Mike at CWI makes reinforced/gusseted lower control arms, and is extremely knowledgeable. AMP is also great.

TT

[KobraKarl]

Tom,

I'm going to step out on a limb here and say I dont think that is an original e-type arm. I just rebuilt the rear suspension in my car (bearing/seals) and had the oppourtunity to examine mine very closely. Three thing look different,

The original weld procces seemed to employ a sort of massive electro /fusion joining of the forging to the tube, this leaves about a 5/16 welded metal flange inside the tube, I could not see any sign of that in your photo.

The original also has a very regular 1/4 "wide by 1/8" high bead around the outside perimeter of the joint ,very smooth ,no bumpy bead. I could not see any sign of that either.

The break looks jagged and the bits of broken weld bead dont look like what I have.

Tom, I certainly am no expert, but they do look different.

Kk