Bad repeated lurching motion when accelerating

[steamship]

Originally Posted by Horrgakx

Although the ARB drop links might be a good shout, I'm not 100% on board with that. Although the noise could be as a result of ARB drop links as the noise happens with sudden vertical movement (I recorded the sound and will post later), but would they be the cause of the bad jerking / lurching?

I somehow missed the lurching part. With that said, I just came across a thread using the same term, but unfortunately no resolution in it. Link as follows:

https://www.audiworld.com/forums/a8-...issue-2876581/

I also forgot to include the link to the other thread regarding the grating noise:

https://www.audiworld.com/forums/a8-...links-2881584/

Originally Posted by Horrgakx

Ps - the diagram you posted is one of a possible two sets. The only difference I can see between the two is the inclusion of a vibration damper. But i cant see what links the appropriate drawing to the vehicle...?

The second set that you're referring to is for the armoured version of the car. The first set is for every other variation, regardless of engine. Stupidly, I provided the image of the armoured set, which I've now changed, but the part numbers are correct for yours.

[Horrgakx]

I had a reply from the garage, the parts they fitted first are 4H0407151C & 4H0407152C (#1 in the diagram above).
Then yesterday they changed 4H0407693G & 4H0407694G (#10.& #11 in the diagram above).

#7 could be a culprit because that looks like it transfers longitudinal load into the car AND it could be making the noise too....
What do you think?

[ainarssems]

I would be more inclined to think lurching is more related to transmission or engine. Engine mounts, gearbox mounts, rear diff mounts, propshaft middle bearing mount. Or gearbox/ torque converter itself. Curved bottom suspension arms can also affect if the bush is worn but then you also likely to get vibration when braking.

[steamship]

Originally Posted by Horrgakx

I had a reply from the garage, the parts they fitted first are 4H0407151C & 4H0407152C (#1 in the diagram above).
Then yesterday they changed 4H0407693G & 4H0407694G (#10.& #11 in the diagram above).

At least that explains the cost, with around £1,200 in parts, so far.

Originally Posted by ainarssems

I would be more inclined to think lurching is more related to transmission or engine.

I think this is one where you really need 'bum on seat' to feel it for yourself, as 'repeating lurching motion' is open to interpretation, and leads to more questions - how long does it last, is there a frequency to it, is it speed related i.e. move off slowly/quickly, is it weather related i.e. cold/warm, is it engine/transmission related i.e. cold/warm, how long does it last and is that speed related, how severe is the lurch i.e. you can 'feel' it as a driver or you can notice it as a passenger.

[Horrgakx]

The garage have given me the following part numbers which have been changed;


And here's a video - with audio - showing;
1) The noise over speed bumps
2) The jerking / lurching motion
https://youtu.be/-ySEm_HFHRs

[steamship]

That is a lot worse than I was thinking, as I was thinking it might only have been a slight noise and lurch.

With that video, maybe ainarssems can narrow down the likely culprit(s).

[ainarssems]

Video does not help much, it's not the same as real life, especially on a crappy small cheap phone speaker. Maybe would be better on proper speakers. The only thing it does, is that timing kind of shows that at least one of issues is at the front of car.

I have come up with another possibility however, which could tie both issues together, but it's just a speculation.

I am thinking of front driveshaft inner joint by the gearbox. Not sure what D4 is using, CV joint or tripod, I guess tripod, but in either case it could be dry or worn/damaged and make noise when going over bumps as driveshaft angle and length changes and it needs to slide in and out. And also under acceleration if it has play and shifts off centre or if it's binding due to dried out grease/lack of lubrication, it could be the cause of lurching. Does the lurching effect change depending on ride height?

[Horrgakx]

Thanks for your reply. Definitely need to start looking at other components, especially the drive as you mention. It's back into the garage in a couple of weeks and I'll ask them to look at exactly that side of it.
I've not tested it with the suspension raised, I will do though.