What could cause bodyroll in live axle setup?

[Tom86]

Hi everyone,

I got a question for those that know suspensions. I recently installed a new rear suspension setup in my Sprinter. Rather than just a normal spring and shock setup. This new one come with a adjustable spring perch like
THIS
The spring rate is 6kg/mm and I have a whiteline swaybar.

My problem is when corner at high speed, I get significant body roll and floating/unstable feeling in the rear. What could be the cause of this? The car is not super low it still have about 15mm gap between wheel arch and tires.

Thanks

[oldcorollas]

i guess the body is rolling?

but seriously... is it feeling floaty in the rear because the front corner is tucking under and unloading inside rear tyre?
or is the front being well behaved and the back just feels light?

if front is ok, then rear swaybar is too heavy and you are unloading inside tyre..
if front is crap, then the rear bar is too big compared to front bar and unloading the inside wheel ;9

this is just my vague guess tho

[Hack]

Have a read of this, very good info

http://www.toymods.net/forums/showthread.php?t=376

Hack

[Tom86]

The front is good. I can feel that there are heaps of grips (doesn't want to slide or anything) and all tires are on the ground. It is good at lower speed, but as soon as you try corner faster it just goes to shit with the body roll

[MWP]

There is nothing wrong with body roll if the car grips ok...

What happens if you corner too fast with neutral accel?
Understeer or oversteer?

[edit]
Oh, and where did you buy the adj perch?

[ill-minded]

also, on top of where you got the perch from, is the whole thing made of aluminium or just the collars?

[Tom86]

What happens if you corner too fast with neutral accel?
Understeer or oversteer?

It actually pretty neutral. You can actually get on the power pretty early and not have the rear end losing traction.

Oh, and where did you buy the adj perch?

I bought it while I was in Japan. It the rear setup for a Greddy Type S Coilover kit.
Yes all aluminum very light.

[Joshstix]

Is it just unloading the side enough from roll that the spring is no longer captive and the axle is just hanging?

[The Real Roadrunner]

what dampers are in there?

are they soft/hard? adjustable? does the valving feel good at all other times?


cheers
linden

[Tom86]

Is it just unloading the side enough from roll that the spring is no longer captive and the axle is just hanging?

No too sure exactly what you mean, but you just gave me an idea. I think maybe I haven't adjust my shock absorber length to match the length of the spring. That is shock is too long so when I corner one side of the spring is no longer captive?? I'll try adjust the shock length on the weekend .

[oldcorollas]

if the shock is not keeping the spring captive.. then when it does keep the spring captive, you will lift the wheel off the ground...or will come much closer to it... if the shock is toppign out, then you have a sudden change in spring rate from 6kg/mm to infinitekg/mm = funny handling..

[RobertoX]

Do you still have the standard bump stops? They may be too long. (to see if it is touching have a look on the spring perch on the diff housing and see if there is a fresh bit of paint where the bump stop has rubbed off the dirt and crud)

What size is the front bar and what are the rate of the springs (front)? 6kg springs on the rear is fairly stiff for a street car.

[Stefan]

I wonder if the roll centres have been upset by this, or other mods.

These symptoms sound similar to what happens at the front of a car with struts when the roll centre has been lowered by lowering suspension without using RCAs - but i'm unfamiliar with how the roll centre is affected by lowering a live axle.

[ra23celica]

I think oldcorolla's has hit it on the head. Have you wound the spring platform/ring down to its lowest setting, ie. lowered the rear end as much as possible? If so, then without shortened shocks to match, your springs will not be captive when your shocks are occillating at the upper limits of their travel.
Easy way to test this theory, wind the platform ring thingy upwards, that is, raise the rear ride height and go through the same set of corners that gave you the weird handling at the back. If the problem has disappeared, you now know what it is...

[Tom86]

Last night I've try driving around the same corner again. Mid corner I can hear noise that sounded like the spring has separated from the perch as the weight move from one side to the other. So I think it is quite possible that when the shock is fully extended the spring is no longer captive?

What you guy reckon is the easiest way to adjust the spring/shock height so that they match perfectly?