Outer Limits 4x4 Board

I have searched but I am after a bit better clue on a shimmy in my patrol. 99 GU, 2inch lift, caster bushes etc. (its a wear issue, not a lift issue)

It has developed a bad shimmy when hitting a bump while cornering at speed. Its started only a couple of months ago and got worse over time to the point of being scary.

I have just replaced the panhard bushes, new shocks, steering dampner good, caster bushes seem good when levered with a tyre lever. Wheel bearings are okay, Tyres are a bit scrubbed on the outsides.

When the big washers are levered on the back of the arms, the bushes seem to have a little bit of movement, Do they wear? and what influence do they have on the above issue.

Is there a way to test kingpin bearings and would they influence this?

The shimmy feels like something loose in the front end (nothing I can find is) which is causing the front end to shake which then transfers up the tie rod to the chassis of the car, and is most violent throught the steering wheel.
Any other suggestions?

I had the same problem and did all the same checks. Found it was a tyre issue, replaced the suspect tyre now shimmy at 70-90km/hr is gone.

Another reason can be from your suspension sagging this will cause a headshake to start as the caster alters with changes in lift.
Headshake and shimmy are two different things as well, shimmy is usually their all the time and headshake happen usually after hitting a pothole or similar.
If all bushes are fine look at your caster , if you have no luck email or pm me an image of your pinion side on and i will tell you if it is caster issues.

Headshake sounds like what it is. I know the standard 85km wobble and have learnt to live with that.

When you have it set up correctly their is no reason it should ever have headshake or shimmy.
Do you have a bump stop measurement from the underside of your front bumpstop to the diff and what caster Correction did you have fitted.

The gap between the top of the spring hat and the bottom of the bump stop is 85mm. The Pinion angle is almost flat but it is hard to get a photo of it.

I am not sure what caster angle the kit it is.

Hope that helps.

SuperiorEngineering wrote:Another reason can be from your suspension sagging this will cause a headshake to start as the caster alters with changes in lift.
Headshake and shimmy are two different things as well, shimmy is usually their all the time and headshake happen usually after hitting a pothole or similar.
If all bushes are fine look at your caster , if you have no luck email or pm me an image of your pinion side on and i will tell you if it is caster issues.

But as your suspension sags won't you gain more positive caster? Also while you're here, what sort of caster readings should I have with a 4" lift and your drop boxes? When I first fitted the suspension and wheel aligned it I had about 1/2 a degree positive caster but I reckon I should have a bit more once the springs settle and it drops a bit?

Andrew_C wrote:The gap between the top of the spring hat and the bottom of the bump stop is 85mm. The Pinion angle is almost flat but it is hard to get a photo of it.

I am not sure what caster angle the kit it is.

Hope that helps.

Standard GU is approx 50mm Gap so if you have only 85mm it means you are approx 35mm above standard , if you have caster bushes fitted with 35mm lift it will almost certainly cause a headshake .
It is a common problem we see when suspension sags.

Tire size also has a relation to the caster , if we sell a 5 inch kit with 35 or bigger tires we rarely supply a 5 inch drop radius arm but more towards a 4 inch arm.

The answer to yours is to replace your coils or fit coil spacers .
If you want to stay the height you are put standard radius arm bushes in.
The pinion should be slightly pointing up towards the back.

Generally we dont look at caster readings as all vehicles drive different, from a manual i think it was approx 2 positive.

We have seen some trucks with perfect caster readings almost undrivable and others nowhere near factory readings and they drive sweet.
Makes little sence but its fact.

Thanks for your help, If you were a little closer, I certainly would come and see you.

SuperiorEngineering wrote: We have seen some trucks with perfect caster readings almost undrivable and others nowhere near factory readings and they drive sweet.
Makes little sence but its fact.

Yeh mine drives pretty sweet with the drop boxes. Thanks for the info.

I have just pulled a set of factory radius arms with 3 degree castor bushes out of my 3" inch lifted gq LWB it shook between 70 and 80 i replaced the arms with superflex arms and the wobble is gone !! I read somewhere a while ago that as a general rule 1 degree of castor correction should be implemented for every 1 .75 inches of lift !??! I'm no expert but if you have 35mm of lift go back to factory castor bushes ........just my 2 cents

Yes, simple things like wheel balance or a bent rim can give you the shakes. All of my shakes didn't go away until I put in new shocks when I did the lift. LF one was complete gone and I figure it was what was causing the shakes.

I always thought it was 1 degree of castor correction after the 1st inch of lift.

eg.
5" lift = 4 degree of castor
3" lift = 2 degree of castor
and so on,

But i'm a lux driver so I could be wrong.

I didn't do the castor correction after doing the OME 2" lift. I did take it in to be checked out and was told my Safari didn't need castor correction. She handles as well at 100 k as at 130 k or 50 k.

you sound like you have the same problem as what i get from time time, death wobbles that feels like their something majorly loose in the front end.