C5 X7 HDi240 (AM6) – Speed-dependent scraping & heavy vibration during right turns under load

[marsalek]

Hi everyone,

I’m looking for some technical advice regarding my C5 HDi240 (Aisin AM6 automatic transmission). I’m dealing with two symptoms that might be related:

1. The Noise:
Between 45 and 55 km/h, there is a grinding, speed-dependent noise when driving straight. It gets quieter at higher speeds. It occurs regardless of whether I’m accelerating or coasting (on/off throttle) and persists in both "D" and "N". It seems to originate from the front-left, though acoustics can be deceptive. Crucially: it gets louder in right-hand turns and almost disappears in left-hand turns.

2. The Vibration:
When turning right under load/acceleration, the front end vibrates violently (seemingly near the front-left wheel). I have to lift off the throttle immediately; the vibration stops as soon as I straighten the wheels. This does not happen during left turns.

What I’ve done so far:
The car has 260k km on the clock, so I recently replaced the front wheel bearings (FL and FR) as well as the upper and lower "ball" joints on both sides. Unfortunately, the noise and vibration remain completely unchanged.

My Questions:

Could this be the inner CV joint on the left driveshaft?

Could it be the output shaft bearing of the transmission? (But would that be so heavily dependent on steering direction and load?)

How can I definitively test/diagnose this?

What is the procedure for removing the driveshaft from the Aisin AM6 gearbox? Does the transmission fluid need to be drained first?

Any tips or insights would be greatly appreciated!

Best regards,
Karel

[mickthemaverick]

In addition to the potential causes you have mentioned, all of which are possible, have a look at the brake back plates and make sure you are not getting fouling when the steering is turned to the right!

[PaulC5]

The brake pads might be a bit seized, does the noise alter if you lightly touch the brakes ?

[marsalek]

Thanks for the hints! The brake pads are OK, I had removed the brakes when doing the wheel bearing and they were OK. The brake back plates are fine too. I removed and reinstalled them for the wheel bearing repair and they were untouched, so not scratching anywhere.

I initially used wrong word "scratching" for the description of the noise, but this is more like grinding. What usually a worn out wheel bearing is responsible for.

[PaulC5]

You need to test the outer cv joints, when worn they can give a grinding/knocking noise, worse when turning in one direction than the other. Also make sure the hub nuts are fully tightened to the correct torque but I think you will have done this when replacing the wheel bearings.

[marsalek]

PaulC5, thanks for the ideas! Hub nuts are OK, but I am suspecting the CV joints I do not have the feeling how much play and in which direction the whole shafts and joints may have Will have a look at it.