Rear-end Problems on Contemporary, Jag Rear-end

[Davidm]

Hi,

Thanks for reading this tread.

I have a Jaguar rear end. The Axel has a large metal housing where it meets the tire, two small metel rods attach at the top and bottom of this housing by a small bolt. The top bolt has fractured off. I am able to remove the bolt and reattach the rod but it seems to break off about every two months or so. Usually when I am accelerating. I have a 427 SO.

Does anyone have a good fix? Should I just keep replacing the bolt? Does anyone know what the real name for what I am describing? Any help is appreciated.

Thanks,
Davidm

[Dominik]

David,

you may check the ERA Cobra web-site to better identify the parts you are talking about.
I am using the same axle as you, though do not know what you mean.
Maybe it's the Watts linkage used on later CC Cobras.

start here:

http://www.erareplicas.com/427/rsusp.htm

Bob from ERA is not at the PC yet, so I (the servant) jump in.

No bolt is supposed to rip off and beeing replaced from time to time!

Good luck,

Dominik

[tonyvda]

It doesn't sound as if the suspension is standard Jaguar XJ6 series 1, 2 or 3 . The diff and driveshafts may be standard but the suspension arrangement sounds very much different. Are the brake discs inboard or out board ?

Cheers,

Tony.

[Bob Putnam]

David,

Take a look at the picture at the top of this page:
http://www.cobracountry.com/amp/home.html

Which type of hub carrier does yours look like - the left or right side?

Here's another picture of the right side - which I think you've got.

[rdorman]

I want to be clear about this before I begin. Jag makes a nice independent rear suspension. Is it perfect, no. But then what is.

In looking at the pictures of the suspension with the watts linkage I have nothiced that all of the attachement points are in single and not double shear. This is BAD. bolts are tension fastners and not sheer pastners. If a bolt is to be used, it should be in double shear. Use a good washer of sufficient hardness between bolt head and all moving, bearing surfaces.

Since you may be stuck with single shear bolts, this is about all I can think of to do. Use aircraft bolts of say 380,000 tensile strength or better. Not aircraft type, the real NAS etc type bolts. Use the appropriate ( size and strength ) washers and lock nuts ( if needed. Use anti-seeze and torque to the correct foot pounds for the bolt in use ( ask the dealer where you get them, locktight will also be OK, no need for the high temp stuff for these bolts ). The bolt holes must fit very closely. This include the one in the heim joints. Slop here will cause problems. There must be NO threads in the bearing area. Plus the unthreaded area should protrude at least half the diameter of the bolt into the hub carrier ( from the picture it appeared that this was where the threads where housed ).

Also, check you suspendion for bind in full bumb or droop. You dont want the watts linkage in this car to be the limiting factor. Unless the suspension has some sort of strap or something I am not seeing the bumb and droop travel is probably limited first by the shock.

In looking at the picture from the link above...I may be showing my ignorance here about jag rear end but it seems to me to a flawed design for high horsepower cars. The idea of uses the half shaft as effectivity an upper location support is ludicrous. Add compression and tension stresses to an allready highly stressed member in torsion. This must be one heavy half shaft!

I have seen some jag suspension correctly ( at least in my humble opinion ) modified with a new hub carrier ( FLOATING half shafts, At least out board ) that have four locating rods ( A arms, etc ) attached to the frame at four points. I seem to recall one that had five which may reduce the stress put on the connecting members but I can think of a few problems that might be run into with this.

Happy motoring.

[Bob Putnam]

Originally posted by rdorman
In looking at the picture from the link above...I may be showing my ignorance here about jag rear end but it seems to me to a flawed design for high horsepower cars. The idea of uses the half shaft as effectivity an upper location support is ludicrous. Add compression and tension stresses to an allready highly stressed member in torsion. This must be one heavy half shaft!

While the half-shafts are fairly highly stressed, they are quite up to the job. Failures of properly shortened shafts are extremely rare, and if the shafts are designed correctly, they don't fail catastrophically. The u-joints that Jag uses are heavier-duty than any that Corvette ever used, even in their old 427 cars, and Chevy felt they were reliable enough to use all the way up to the C5s. Weight-wise, I doubt whether our shafts and joints are significantly heavier than a CV system.

Chassis weight loads are only about 10% of drive loads and actually decrease on the outside wheel during cornering to near zero.

[rdorman]

I Love it when I am right! I am showing my ignorance! I meant to qualify my comment about the Jag design by saying the 'original' Jag design . Don't be defensinve Bob, I was not talking about ERA. I have no preference yet, but I am forming one for my next purchase. So play nice! And ERA is in the running for my next car. ERA makes a nice car, I would use you standard Jag suspension but if cost was no object, it would have a different carrier and upper suspension pieces with good CVs. My preference. I am sure the Jag guys get paid a lot more to design then I do. Make that a huge amount more since I don't do professional design work!

I am not sure about the reference to vettes means. While they where great cars, they where not exactly a banner of reliabilty. Since I can not picture the Vet suspension of the top of my head I can not comment on how the suspension attaches. If they attach top and bottom as I described then I would expect the u-joints for a Jag rear end would have to be stronger given what they are asked to do. Plus the lower arm/s would have to be a lot stronger and relatively compliance free ( Ahhh, all is relative! ).

There are some nice mods to the stock rear end around including the ones done by ERA. I suscribe to the Carroll Smith camp I think that in a 'perfect' world, he would agree. But that 'perfection' comes with a very, very heavy price and in the end, almost all of us must comprise between what our version of perfect is and what will work effectivity but at a reduced price. Jag, like everyone else, has its problems.

Cut and paste from ERA sight:


"The original Jaguar XKE suspension also used a subframe and trailing arms - which worked quite well in the lower powered car. We found it necessary to stiffen up the mounting system to make more precise handling.

Some other kits also use the Jag suspension, but because of space and design restrictions, don't use a trailing arm. This puts the lower control arm into stress modes for which it was never intended. With power on and power off, the arm will flex forward and back, changing the toe-in simultaneously. Not great for predictable handling! "

Please note that the optional carrier hub and watts linkage as drawn on the ERA sight from Contemporary Classics/Burtis Motorcars does appear to have the top connection made in double shear as it should.

Back to Dave. Check out the things that I suggested in so far as bolts, suspension travel, worn parts or damaged parts ( assumed that this was looked at first ) and fit. If all else fails try the bolts and installation I recommended. Or don't power shift any more!

[Dominik]

rdorman,

I appreciate your input. I would love to build a "budget" version of the Jag rear end featuring an upper a-arm.

If you have a proposal how to build it let me know.

I am thinking about a mounting point for an upper a-arm at the existing alunimum housing to create a similar version of a Group-C axle as seen in the pic (a little out of focus, sorry).

Bob,
does ERA have plans for that?

Dominik

[Bob Putnam]

Dom,

I actually designed our outboard-braked rear with an upper link at first, but also made it so it the plunge distance of the half-shaft would be at a minimum. I did it so well that the upper arm is essentially redundant if the length of the half-shaft is constant. In the end, I chose to keep everything simpler (and cheaper) by not using an upper radius arm. Because I bolt on the upper link attachment, my hub carrier is still amenable to a radius arm, but our subframe doesn't have provisions, and would require a curved arm to fit. More weight...

RDorman,

The Corvettes used the same system as the Jag - the half-shaft doubled as the upper link - from '63 to the C5.

We make our half-shafts by taking the original pieces and turning down the ends to fit inside a heavy piece of tube. They are a press fit for about 3", then they are welded. If the weld breaks, the axle may spin, but it tends to stay together. The suspension won't "fall over" - you just lose the ability to transmit torque. All of that is quite academic though. Since we went to a heavier tube (quite a long time ago), we've never had a problem - even with guys using slicks for dragging.

[Dominik]

Bob,
very nice, very nice!

Which half shaft do you use for that axle? Or are these the ones described later in your reply?
You need to allow for some movement at bumps somewhere, don't you?

I used the same method of shortening the shafts. Torque is transmitted via the circumfence of a pipe. Double the diameter "D" and the pipe will stand D**4 (!) more torque.
(D**3 for solid materials)

Just look at those tiny half shafts from the Group-C. That car was raced before with an all aluminum Chevy with 500 cui and fuel injection.

Those in the pic are more prone to go apart than the thicker original units, but do not destroy as much if they fail.

Are we still with the topic?

Dominik

[Bob Putnam]

Dom,

Yes, we use the same half-shaft design on that rear. Actually, exactly the same pieces with a spacer in place the inboard rotors.

I am alway amazed at how small the shafts are too. Besides the ease of mating to the CV joint splines, I suspect that they are small to allow a little twist, decreasing the peak and cyclic loads on the transmission pieces, etc. I can't imagine that the rotational inertia difference would be worthwhile, especially if the solid pieces were replaced by a carbon-composite tube.

[Dominik]

My mistake:

it is D**3 for solid forms as well as for pipes.

Bob,
I should check your site more often.
I like the chassis strenght article!

Dominik

[CorvetteMan]

DavidM,

Wondering where your other Contemp buddies are when you need help? They always seem to be boisterously noisy with other topics...

[zimmy]

We're here. I just don't have anything to add that will help the situation. Sorry.

Zimmy