Help Please S4 B8.5 - Shaking under braking only in sport at high speed

[Andymanic]

Hi there. Got a real head scratcher, could do with some help/advice.

I have a 2013 S4 B8.5, and on certain occasions I have a shaking/shuddering when lightly braking at speed. It seems to only happen in sport mode, and only after driving fairly hard and normally over 100. It varies in strength too, sometimes it's a light shake, sometimes it feels like a wheel is loose and falling off. When it does happen, once it goes away it won't happen again on that drive. I feel it through the whole car, nothing through the brake pedal alone so doubt is brake disk related as I don't feel any vibration in normal mode, nor at any other speed.

I'm quite stuck on this one. The car has the sports active suspension so I'm guessing there is a bushing that's worn, and the active suspension in sport mode exaggerates the problem but I haven't had a chance to jack it up, take the wheels off (I believe its coming from the rear, possibly rear left) and check everything. I can feel a slight vibration while driving in the whole car especially on the motorway, so swinging to that. Maybe wheel bearings? It passed an MOT in late July so assume most is fine.

Anyone have any suggestions?

 

[V6_Man]

Hi there. Got a real head scratcher, could do with some help/advice.

I have a 2013 S4 B8.5, and on certain occasions I have a shaking/shuddering when lightly braking at speed. It seems to only happen in sport mode, and only after driving fairly hard and normally over 100. It varies in strength too, sometimes it's a light shake, sometimes it feels like a wheel is loose and falling off. When it does happen, once it goes away it won't happen again on that drive. I feel it through the whole car, nothing through the brake pedal alone so doubt is brake disk related as I don't feel any vibration in normal mode, nor at any other speed.

I'm quite stuck on this one. The car has the sports active suspension so I'm guessing there is a bushing that's worn, and the active suspension in sport mode exaggerates the problem but I haven't had a chance to jack it up, take the wheels off (I believe its coming from the rear, possibly rear left) and check everything. I can feel a slight vibration while driving in the whole car especially on the motorway, so swinging to that. Maybe wheel bearings? It passed an MOT in late July so assume most is fine.

Anyone have any suggestions?

Sounds more like warped rotors to me if it does it at speed.


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[Andymanic]

Sounds more like warped rotors to me if it does it at speed.

I would agree if it did it at speed in non-sport mode, but it doesn't. I don't feel any vibration, and I don't feel it through the brake pedel either.

 

[Dippy]

If it has ADS with adaptive suspension then you could try driving it in different modes to see what effect it has.

 

[Andymanic]

If it has ADS with adaptive suspension then you could try driving it in different modes to see what effect it has.

It doesn't, just the D/S/M gearbox modes which change throttle response, steering and I believe suspension dampening. But like I said it only happens in S mode.

 

[Dippy]

ADS is what changes throttle response, steering, suspension, sports diff and ACC settings. Dynamic switches the gearbox to S. My suggestion is to confirm that the gearbox has nothing to do with it. Temporarily reconfigure the individual mode to select D, but different suspension settings. If on the dynamic setting (or whatever its called - the firmest one) the vibration still occurs then it proves its the dampers?

 

[Andymanic]

ADS is what changes throttle response, steering, suspension, sports diff and ACC settings. Dynamic switches the gearbox to S. My suggestion is to confirm that the gearbox has nothing to do with it. Temporarily reconfigure the individual mode to select D, but different suspension settings. If on the dynamic setting (or whatever its called - the firmest one) the vibration still occurs then it proves its the dampers?

So I don't have MMI, and the "Car" menu doesn't have any options to configure any of that.

The good news is I finally had the chance to jack it up.

The lower control arm bushings are SHOT. Like, next to nothing left in them. This passed an MOT almost exactly a month ago...