I finally saw a Jag IRS setup
 

Well I went to the Carlisle show this week end. Glad I went, wish I had had even more time there.

I got to see several Jag IRS setups. I have got to tell you I was shocked. The inboard brakes look near impossible to service, although it can be done, and I was expecting that. But what blew me away is the lack of any upper arms to hold things together.

If a U-joint were to break not only do you loose the ability to connect the brake to that wheel, but the wheel is going to tilt in. What a death trap waiting to happen. No way you are going to survive if this happens at full power and moderate speed -- IMHO.

Is this a common known no $hit or am I totally wrong.

Olddog - I would have to agree with you on a couple of observations if you use an IRS setup that is not set up for massive torque (especially from a big block).

I have a Jag XKE Series 2 IRS on my Contemporary and it has been modified to eliminate some of the problems (i.e., full power hit to the rear).

I agree that the inboard brakes are tough to service, but not impossible...does take a lot of patience to work on, though. I changed over to larger calipers during my rebuild. I did not want to spend more $$ to go with outboard calipers...

Stub axles are chrome moly to handle the torque over the standard setup, and the original half shafts, U-joints and hub assembly have been replaced with AMP hardware (courtesy of Accurate Machine Products - George Petrus in Torrance, CA). I also replaced the original A-Arms with a setup from AMP which also is set up to include a Watts linkage setup (hooked up to the frame).

This setup seems to hold up to FE power!

George

Olddog, never heard of a jag rear end axel failing, of course it's possible but with an annual inspection and preventable maintenance, you should never have a problem. I installed the 'rear mount' caliper brackets and they work great, you just pull the carter key, slide out the pads and install new ones...simple. Check my pics.....

Olddog,
You may want to take a look at this Jag-based system on ERA cars http://www.erareplicas.com/427/frsusp.htm. Outboard brakes and a very sophisticated adjustable suspension. Look at how they eliminate your concerns.

Olddog,

Jag rears have been used with good results on thousands of replicas (Cobras and hot rods) and tens of thousands of Jags. The stock axles are very reliable and ERA has made them fail safe. Failure rates from torque application is probably less than the failure rate of CV-type axles, and they never fail from axial loads, which are relatively small.

More information on the ERA rear is here.

We've found the rear brakes very reliable and the pads will last 40K-miles-plus and the rotors much more.

There's a fellow on this forum with an Arntz. Can't remember his username, but his real name is Paul. He posted about a rear u-joint failing and it sent him off roading. Sounded like he was lucky.

rallysnake is his username....

A failure of any major suspension component is not going to be good! But like folks have said, they are tough rear ends. Properly assembled and maybe a few easy mods or two they are very durable. And don't skimp on the u-joints (and please install them correctly!).

I have seen a couple of jag axles beak, but these were shortened and welded pieces and also it was some years ago.I don't recall seeing a factory shaft break. As long as the universals are kept in as new condition the jag setup imo is very reliable and strong to boot!

I've known it since the early 70s. I used to own and work on many Jags.

Did you fabricate those brackets yourself or did you purchase them? What do you do for an emergency brake? What calipers are you using. I'm interested in anything you can tell me about your rear brake setup, as I'm about to completely disassemble mine, and it looks like a bit of a nightmare.

My emergency brake setup is COMPLETELY backward - the handle is on the drivers side of the tunnel. The E-Brake caliper that the outer sheath of the cable is mounted to is on the driver side, and the E-Brake caliper with the inner core of the cable attached is on the Passenger side. I want to put the handle in it's correct position on the passenger side, which means I have to disassemble the entire brake setup and swap the E brake calipers, no? Can the E brake calipers be swapped without removing the brake calipers? This whole rear setup is like nothing else I've ever seen. Anyone got any ideas?

Many say it is a strong system that rarely brakes, but that is not the point, in my mind. The point is that U-joints on driveshafts do break and an axel is going to take 2 to 4 times the torque. They can break!

This design takes the weakest link and ties the entire assembly to it. One simple failure, that assures catastrophic results.

Having worked in the chemical industry most of my life, where safety is taken to extremes, I have learned to recognize a bad design when I see one. I got to tell you this is about as stupid as it gets, as it is so un-necessary.

Are there any modern cars being produced today with this type of design?

Don’t get me wrong here, as I’m not trying to cast stones at anyone’s car here. I am genuinely concerned that this is not safe to be putting big hp through.

olddog,

Interesting speculation.

Consider the following anecdotal evidence: tens of thousands of Jags with that rear suspension have been driven millions of miles since 1962, including the new post-2000, higher powered V8s and many heavy British saloons, some of which were hopped up considerably and raced, and yet if you search, there aren't any reports of the type of failure you predict....

Just a thought.

Do you know of any documentation of the failures you describe?

Just curious,

Tom

I'm sorry, but I think you are getting overly concerned about parts that in real world use virtually never fail. Even if it were to fail, my experience in breaking axles and CV's (high hp formula cars with slicks) is that it happens in first or second gear while accelerating hard in a straight line over bumps where the drivetrain gets unloaded and then loaded very quickly and something will snap. The normal result was that I coast to a stop and get out.

I think a bigger problem is trying to figure out how to get big power to the ground efficiently and safely. When this doesn't happen, THATS when problems occur.

just my $.02

Bob

XRACERBOB
But this design uses the axel as the upper arm. When it breaks the wheel is as loose as if you took the upper A-arm off of your front end.

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.

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. :eek:

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

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

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.

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.