Hey guys. The car is a 2006 Ford Fiesta (Mk6.5). It's making a single knock or "clonk" sound whenever a sharp turn is made while in motion. This does not happen when I turn the steering wheel while the car is stationary. Both ball joints have been replaced and both strut mounts checked with no issues according to my mechanic. Shock absorbers were recently replaced as well. I've been to 2 mechanics so far and they could not 100% identify the cause. My mechanic also test drove the car with the stabilizer links disconnected but the problem was still there.

Here is a video that I found of exactly what I'm experiencing, uploaded by someone else: 

https://youtu.be/5-4bvTYOMAU

I'm struggling to identify the cause of the knock. Could it be the steering rack? I'm a bit puzzled because if it was the steering rack then why is it not making the noise when I turn the wheel when the car is stationary? 

The fact that it only occurs in motion leads me to think that it must be caused by a suspension component that is put under stress during turning while in motion.

Any ideas would be appreciated.

Thanks

The ball joints are not the only swivels. The rubber bushes at the inside of the wishbone could be the problem. A loose wheel bearing can cause pad knock off and the disk can contact the pad and move the caliper, causing a clonk. Engine mounts ok? Have you checked?

16 minutes ago, tomshepp said:

The ball joints are not the only swivels. The rubber bushes at the inside of the wishbone could be the problem. A loose wheel bearing can cause pad knock off and the disk can contact the pad and move the caliper, causing a clonk. Engine mounts ok? Have you checked?

Thanks for the reponse…Visually the bushings seem fine, is there a way that you recommend I could check physically? It's difficult pin point the noise origin as it only happens when the car is in motion and turning, and I can't replicate the sound when it is parked or jacked up. There's no noise at all if I'm driving straight or even hit bumps or brake.

I doubt that it's the brakes as the sound seems to be coming 'within' the car and not from the wheels if that makes sense.

One of the front wheel bearings was replaced recently also. One of the lower mounts was also replaced, not sure if it was the engine or gearbox mount but I'll check.

Would faulty engine mounts cause a noise while turning in motion only? I would imagine that faulty engine mounts will make a noise when driving straight or just revving in neutral also?

Within. Inner driveshaft joint, maybe. Engine mounts broken cause the engine to move. If it hits something, there is your noise. you need to think of the "weight " of the clonk. If it is something heavy you feel it more than hear it through pedals or the wheel. It could be a loose exhaust, for existence  but if it is in the suspension or steering, you should feel it  in the wheel or detect the change in direction  that something loose would cause.

24 minutes ago, tomshepp said:

Within. Inner driveshaft joint, maybe. Engine mounts broken cause the engine to move. If it hits something, there is your noise. you need to think of the "weight " of the clonk. If it is something heavy you feel it more than hear it through pedals or the wheel. It could be a loose exhaust, for existence  but if it is in the suspension or steering, you should feel it  in the wheel or detect the change in direction  that something loose would cause.

When I rev the engine hard in neutral, parked there doesn't seem to be much movement in the engine. I'll try to see if it's any different when I drive.

My mechanic advised that it may be the steering rack, which I'm hoping it's not because it would be an expensive repair lol. I don't actually feel the clonk through the steering wheel when it happens, which is the main reason that I think it must be suspension related. But the 'only occurs while turning' also makes the steering rack seem possible at fault lol so I'm completely confused. 

My plan is to give the tie rods a quick check although I imagine the mechanic would have done so already. 

Do you think it's possible for the steering rack to only clonk when turning the wheel in motion and not when stationary? Sounds a bit unlikely for me since surely the steering rack is doing the same work regardless of whether the car is in motion or not? So if it was the rack then it should make the noise when I turn the wheel while parked as well? Perhaps the load on the steering is even smaller when the wheels are moving so that makes no sense.

The load on the steering is actually greater on the outer wheel. Could be a rack balljoint  or any one of a dozen other things so if you don't possess the diagnostic skills to find it yourself, pay somebody else to do so. It is cheaper and quicker than guessing.