Upset tracking - front wheel alignment 'knocked out of true

[Guy Croft]

I've often heard it said that bumps and kerbs can 'knock the tracking out' on a car, ie: upset the front wheel alignment.

Given that the all steering joints are threaded - how does this happen? Anyone know from first-hand experience of examining tracking that was 'OK' and then 'knocked out' of alignment?

Thanks,

GC

[Evodelta]

Guy,

It really depends on how hard you whacked it in the first place as to if it will be out of aligmnemt and how far. The tolerances from one manufacturer to another vary a bit, but it doesn't take much to move it 2 - 4mm out, remember, we are talking about 1 - 2 tons bearing down on a few nuts and bolts.

What can happen is that the steering arms can bend slightly as can the suspension arms, bolts and even parts of the chassis, but more often where the rack or the suspension arms are bolted to the car will move too as they have no mm perfect location. It is more favourable to have something move or give under these situations rather than bend the chassis or break a component. My experience in this field comes from bending a few cars over the years, replacing the components myself and setting the 4 wheel tracking up too.

If you had a car that was set up perfect, stripped it's suspension and re-built it it would need setting up again as many of the components will not go back in the same place.

Have you been rallying in the Range Rover? ;-)

If you need some pointers as to what and where to go then post up.....

Martin.

[Walezy]

It happens often when the suspension is based on McPerson design and the struts are bolted with 2 screws to the hubs. If you have a free movement in the hole in strut(often this is made to make the adjusting of camber possible) then after hitting something real hard the hub may move a little bit and totally destroy all the toe in/out settings with camber(mostly going to negative setting).

[Guy Croft]

Thank you very much indeed both members for your helpful advice and clarification!

Not rallying, no, sorry! Just bumped a kerb hard and it has been reset - no doubt out-of true for exactly the reasons Evodelta described and although the garage didn't measure a before-after it drives straight now and doesn't scrub the tyres.

GC

[SteveNZ]

I have investigated many accident damaged vehicles for repair and many "repaired" vehicles still presenting wheel alignment issues.

The most common cause, by a huge majority, are bent cast iron hub carriers. Its very difficult to spot a bent carrier with the naked eye, even one that is out 10mm, let alone 1 or 2mm. Its also very easy to bend one. I would find it very easy to believe a decent "knock" could bend a hub; enough to put the alignment out but not enough to notice any damage by visual inspection.

[tmvolumex]

As far as alignment and tracking getting knocked out, the other thing that can happen is the steering rack gets shifted in the rubber mounts. IE the steering rack is mounted to the chassis using steel brackets surrounding rubber mounts. Hitting something can cause the steering rack to shift in the rubber mounts causing the entire rack to be off center. Only the centering of the steering wheel may be affected or the wheel alignment as well can be affected. Other suspension components mounted in rubber can be shifted with a good jolt also.
One thing to check prior to getting a wheel alignment is the condition of all the ball joints and tie rod ends. Recently, I noticed some uneven tire wear on my Fiat 131 and checked the tie rod ends. At first glance the tie rod ends looked OK and even after giving them a good American I could not detect any play. But by applying pressure to the joint with a large, 2 foot long pair of Channel Lock pliers, I was able to push the ball up into the socket portion of the joint. Because the joint is spring loaded it returned to its initial position after unloading. Because the ball could be forced up into the socket, this indicated that the tie rod ends were shot. I replaced them, had the car aligned and wow, what a difference. Steering is now very precise, even when cornering hard and straight line braking is drastically improved, with to wander during braking. Apparently the balls were moving in the tie rod ends during braking and cornering affecting alignment, specifically the amount of toe. Alignment must have been going toe out during braking resulting in a darting effect. Changing the tie rod ends (85,000 miles on them) made a huge improvement.