Car unstable at speed

Issues

Owner of car described that the car was unstable at speed, with some degree of wobble and darting around on the road, and it felt frightening and unsafe to drive above about 70-80 km/h.

Diagnostics

Many people trying to help went down the path of either wheel wobble from tyre wear/incorrectly balanced tyres/non-centred wheels when they were installed on the car, or, just to make sure the car was 100% stock (which it wasn’t).

Description of the issue sounded a lot like issues with insufficient negative caster, however, rather than steering wheel shake.

Further inquiries indicated that the car had a suspension lift installed a couple of weeks prior. That suspension lift did include caster correction and a wheel alignment. No wheel alignment data had been provided to the customer, so the first step was to examine if the caster correction had been applied correctly.

Photographing the front radius arms where they met the front differential/axle housing showed the following when compared to the SuperPro caster bushing installation instructions/drawing of offset radius arm bushes used for caster correction.

Note: without the photo being exactly straight onto the radius arm, it is hard to align it perfectly, however, this shows the offset of the caster bush being incorrect on this arm (the passengers side arm).

As the caster bushes were not correctly aligned with the radius arms on their installation, making the caster of the car worse than leaving it alone after the lift kit was installed. While rare, this can happen and is often a cause of people thinking that a car is inherently unstable after putting in a suspension lift kit.

Resolution

Car was taken back and caster correction was refitted. Car was described as being much better to drive.