Not sure what this problem is!

[The_Laird]

I’m not even sure this is the right section to post this problem. My S8 has started to feel ‘odd’ very occasionally, when accelerating in lower gears. It feels like the rear wheels are briefly going over rumble strips (is this ‘tramping’?) for a second or two, then everything goes back to normal. But the next time I accelerate in lower gears, all is well.

Anyone got any ideas? Perhaps a rear diff or drive shaft issue? But I’m at a loss.

[B@fink]

Bit more info might help with diagnosing (and give the post a bump!). Is it at a specific speed or over a range of speed? Hard acceleration or just gentle? Straight line or turning corners? Just 1 gear or several? Might help track down if it’s a wear, balance or mechanical issue.

[The_Laird]

It seems to happen at lower speeds, and I’m usually accelerating in a straight line without putting my foot to the floor. At a guess it happens in 2nd or 3rd gear.

[Dezzy]

I don't think it'll be tramping Jim, for this to happen it would ned to be gripping hard and slipping slightly that then causes the suspension to bounce slightly, grip, slip, bounce, grip, slip, bounce. So unless you're hard on it and or your shocks are like jelly it's something else.

[moltuae]

I had a similar issue some years ago. IIRC, in my case it started just after I'd had a set of new tyres fitted (on newly refurbished wheels). There was an intermittent vibration, which seemed to come from the rear. It would usually happen after hard acceleration, typically just after joining a motorway. The vibration was severe enough that I pulled over onto the hard shoulder the first couple of times it happened, expecting to see a wheel falling off or a bulge in one of the tyres, but I could see nothing wrong. I gingerly proceeded and the vibration was gone, until the next time I stomped on the accelerator.

I wondered if one of the rear wheels might be slightly bent so I spoke to the wheel refurbishers about it. They told me that they check all the wheels 'run true' before refurbishing so this was unlikely and suggested that I have the alignment checked. So I had my usual garage check the car over and perform a 4-wheel laser alignment, which seemed to make a big difference. They also noted though that some of the rear subframe bushes were pretty knackered. Several months later I had the rear subframe replaced and all the bushes renewed. I'm not sure if the cause was worn bushes, alignment or a combination of both, but the problem has never returned and, following the subframe replacement, the car now feels much more 'planted' when corning.

[The_Laird]

Hmm, just had new tyres fitted! But the ‘vibration’ isn’t anything like as bad as you described, Mark, although Michaela did suggest that my rear end needed sorting out (the car, the car!) so I can imagine that it might be worn bushes. TBH, I doubt anyone else would even notice, but we all get ‘tuned in’ to our cars and anything untoward rings alarm bells.