I finally saw a Jag IRS setup

[olddog]

Tom

Good point.

I'm thinking about so many around here building over 600 hp. With street tires no problems, but what if they bolt on some sticky tires?

There was a story on here a while back about a fellow riding in a car he was looking at buying. My memory is that it was an 8.8" Ford IRS not a Jag. Pretty scary wreck. In this case I think power loss to one wheel was what caused the loss of control. Can you imagine having a wheel tilt in at the same time? Oh yea and you loose the brake on that wheel too.

[Tom Wells]

olddog,

I use a 521 delivering over 400hp to the rear tires. It has run at Sebring, Gainesville and lots of other tracks while accumulating over 19K miles. Oh, yes - the track time is spent using slicks on all four corners and running WFO wherever possible. More anecdotal evidence.

Also, if you really look closely at the Jag rear, you'd notice the lower arm/hub construction will restrain a couple of degrees of freedom if the axle does come adrift. The result is probably not as catastrophic as you anticipate.

I do examine all six of my u-joints once a year or so, grease them and tighten bolts where needed. Nothing that an average high-stress user wouldn't do in the way of maintenance.

No offense here - please don't interpret this the wrong way - but I think this worry is like the old bumblebee theory: from an aeronautical engineering perspective it is concluded that the bumblebee's design isn't correct to allow it to fly. The weight is too high, the wings too small, the aerodynamics all wrong. Fortunately the bumblebee is unaware of this, so it goes ahead and flies anyway...

My experience says there are far more injury and fatal wrecks in the Cobra world resulting from right-foot disease than any other cause due to the very high power to weight ratio, short wheelbase and overuse of the gas pedal. I have personally known several who were killed or injured this way, where no mechanical failure appeared to be involved. HeII, I flipped mine taking driver's ed (on street tires), but that's another story - one Jag rear wishbone was broken at that time from the impact, and was not a cause according to our failure analysis expert.

So unless you can point me to some hard evidence, I'll continue to use mine vigorously on the track and gently on the street!

Regards,

Tom

[cobred]

If you are that worried about it just dont get one with a jag rear, there are many other choices.

[olddog]

Originally Posted by cobred

If you are that worried about it just dont get one with a jag rear, there are many other choices.

I wanted to make sure I wasn't totally wrong about how I assume it works. That's why I put this thread out. If it works as I think, I wouldn't buy one, simply peace of mind for me.

Also if this thread causes someone to go check their car over and they find and fix something that was about to break that's a good thing too.

Sorry if I come across as tossing rocks for no reason. That wasn't my intention.

[G.R.]

There have to be hundreds, if not thousands, of street rods/hot rods and Cobra replicas running the Jag rearend.... let alone in original Jags since "62 or so.
Sure some have failed...due to maintence, negligence or fatigue .... or ignorance/stupidity on the owners part.

It must be he!! to be an engineer (no offense meant if you are one)
If I worried about every little niggly thing about any car I drive I would never drive it, be it the replica or the daily driver.

[double ugly]

I don't think I would have ever crawled into a fighter if breakage was on my mind. Paranoia sets in much later in life.
John

[Tom Wells]

Yetiman,

The car simply rolled to a stop and would not move on it's own power (which kind of surprised me with the limited slip).

Actually this wouldn't surprise me.

When the axle lets go, my bet would be that the top of the tire gets up against the body.

In my car if the tire leans in toward the center, the top of the tire would quickly come into contact with the seat bucket. This would most likely have two effects: The tire would act as though its brake was applied, and second, it would not lean any further. In my car the angle of lean would be very slight since the tire occasionally contacts the body at that point under full deflection... Other car bodies may be different.

That axle failure is not unusual on Jags - probably more common than the u-joint failure. Glad you only had a "Maalox moment" and did not accrue any personal damage CWI http://www.cwiinc.com/index.html sells HD parts for those axles that help a lot.

BTW, Mustang-type IRSs suffer from similar weaknesses, so drag racers tend to go for the live axles instead, and even those occasionally break. A stick shift with repetitive very hard launches at a drag strip using slicks is not a good application for an IRS.

Regards,

Tom

[olddog]

Originally Posted by Tom Wells

olddog,
Also, if you really look closely at the Jag rear, you'd notice the lower arm/hub construction will restrain a couple of degrees of freedom if the axle does come adrift. The result is probably not as catastrophic as you anticipate.

Since I only looked at the thing and did not have the ability to take it apart, I may well have missunderstood some things. I could tell that the hub would not turn left or right, but it looks to me like the top will tilt in with nothing to restrain it (no axel). Am I wrong?

It does look to me like ERA modified the design to minimize my issues.

I can say if it works like I assume, I wouldn't choose it, but if I already had it I would use it. I would be cautious with it, but that's me.

Buy the way I like the bumble bee analogy. You may have me pegged, but again I wouldn't design an air plane based on the bumble bee as a starting point with so many other better examples out there.