AK rear suspension

[kev]

THere is a tie bar goes from the outer end of the bottom "wishbone" by the forward bottom damper mounting, to a track rod end which fixes onto the chassis forward of the diff. Does anyone know what this does? AS far as I can tell it has no obvious function, the rear track is set by the shims on the inner lower mounting to the diff, the torque from the wheels is taken by the bottom suspension arm or does anyone know different?

Still grinning Kev

[interestedparty]

Is the diff rubber mounted on the AK? if it is the bar might be there to keep the whole suspension unit in position under heavy loading.

John

[kev]

THe diff is monted up solid onto the chassis, no rubber bushings.

Kev

[interestedparty]

>THe diff is monted up solid onto the chassis, no rubber bushings.

Well that is strange, is there quite a bit of compliance on the radius arm bushes? There would need to be or the suspension movement would be restricted due to it being pivoted in two different places, ie at the inner wishbone pivot and the radius arm pivot, so as the wheel moved up or down it would be pulled forward by the radial action of the radius arm. Curious, I expect there is a good reason for the arm to be there, but can't guess what it is.

John

[wilf]

Well, it is a radius arm, many kits don't bother with them but Jaguar must have had a reason for fitting them originally. Also not many kits properly support the inner wishbone mounting bracket, but I won't go there.
It is very difficult to get the proper geometry for them on a cobra, which is why they tend to be fitted with big compliant bushes.
I can only suppose, not being a suspension guru, that they are there to reduce the bending moment in the wishbone under heavy loads in the fore and aft plane such as full bore acceleration or braking.

Wilf

[russell_ram]

Kev,

As the diff is solid mounted to the chassis this forward tie bar is totally redundant.

In the jaguar installation, the tie bar restrains the fore/aft motion of the diff cage, which is rubber mounted to the body. As tie lower arm and drive shaft, which forms the upper suspension arm, are both fully mounted on roller bearings with no compliance and your diff is mounted solidly into the chassis, there is no fore/aft motion of the hub possible (unless the bearings are worn). The tie rod therefore does nothing.

Furthermore, if you have one fitted and it's inner/forward mount point is not on the same pivot axis as the lower wishbone pivot, it will prevent the suspension moving up and down to some degree. This is controlled by the compliance in the tie rod rubber bushes. In the worst case, if the tie rod isalong way off the wishbone axis and it is rose jointed, the suspension will not move up/down at all. Imagine the three pivot positions (two needle rollers on the lower wishbone inner and the third the forward end of the tie rod) as three hinges on a door frame. The further out of line they are, the less chance there is of the door opening without something bending. This could either be the rubber bush or the chassis mounting points in your case.

If you're going to fit them, make them as long as posible, get the forward/inner mouning point as near to in-line with the lower wishbone inner pivot as you can and make at least one end compliant (ie rubber bush). However, as I said at the start, making them compliant means they take no load. There's plenty of Ford Pop hot rods etc (and Cobs) running around without these rods fitted, although they do provide some security should all your diff bolts fall out (which they cant because you've lock wired them in like they're supposed to be - right?).

Russ

[russell_ram]

'that they are there to reduce the bending moment in the wishbone under heavy loads in the fore and aft plane such as full bore acceleration or braking'

Wilf

Not with big rubber bushes in them, chap

Russ

[interestedparty]

"Well, it is a radius arm, many kits don't bother with them but Jaguar must have had a reason for fitting them originally"

In a Jaguar the whole rear suspension is mounted in a subframe that is rubber mounted to the bodyframe. Because of this the radius arms are fitted and help to keep the subframe in position under heavy loading. As soon as the suspension is solidly bolted to the chassis the radius arms would seem to me to be superfluous, even an actual nuisance in as much as they can interfere with the suspension geometry.

John

[wilf]

Told you I was no suspension expert.


Wilf

[graham]

I think it was Dave that gave a reply about all this in a previous thread a few months ago. I have got these radius rods they are fiited from the lower wishbone outer to the chassis but at an angle towards the middle of the car. They're quite long rubber bush at axle end and rose joint at chassis end. I guess the chassis manufacturers must have but them there for a good reason???

Graham