Extreme "bump steer"

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Discussion

EricE

Original Poster:

1,945 posts

128 months

Tuesday 30th June 2015
quotequote all
We have a '07 R56 Mini Cooper S with 40000 miles, mostly city and short range driving.
The car left the factory with the sports suspension and mechanic locking differential option.
It sits on OEM 17" wheels, fairly new non-RFT Pirelli Pzero neros with correct pressures. The last alignment was around 20000 miles because I hit a pothole at speed. It didn't "pull" to any side, that alignment was done just to be safe.

Lately the it has started to exhibit "bump steer" to the degree where it is outright dangerous because a pothole could launch you into oncoming traffic if you're not careful and only have one hand on the steering wheel. My family members refuse to drive it until the issue is fixed.
Torque steer is also worse than before but not a problem and likely due to the LSD wearing out.

I’m wondering if anybody has an idea what could cause the bump steering effect. Shocks shot? Alignment required? Maybe a broken steering rack?

I should also note that one of the front wheels, I believe the outer one, starts to "hop" (jump) when I take a corner with serious speed, rather than just going into controlled understeer as it used to.

Edited by EricE on Tuesday 30th June 21:30

texaxile

3,289 posts

149 months

Tuesday 30th June 2015
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From experience, I suffered horrific "bump steer" in my Ford Escort and it was due to the lower arms being shagged out. It got to a point where even going over a drain cover pulled the wheel out to the OSF. Upon inspection all the rubber bushes in the lower arms on both sides were effectively missing / perished. After replacement the car was absolutely fine.

I'd wager lower arms or perhaps a bush has popped out of its housing. the way to check if it is a shock is to check the "rebound" when you push down on the wings is noticeable, and for any oil leaking out of it.

I am not a professional mechanic however, and am merely recounting my experiences. This is a great section of PH with some expert knowledge, so I'm just speculating based on experience. Hopefully another BM will be able to point you in the right direction or substantiate what I've already said.

I think the bottom line is that it's not going to be horrifically expensive to fix and hopefully something relatively simple. If it was a busted rack you'd have power steering fluid everywhere and the steering would be noticeably "heavy". I also doubt the LSD is suspect because they are pretty hard wearing ,and if it is a problem with the lower arms or suspension, it would exacerbate any torque steer.



Edited by texaxile on Tuesday 30th June 22:41

andyiley

9,106 posts

151 months

Wednesday 1st July 2015
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EricE said:
due to the LSD wearing out.


Edited by EricE on Tuesday 30th June 21:30
After 40,000 miles!

Really?

EricE

Original Poster:

1,945 posts

128 months

Wednesday 1st July 2015
quotequote all
andyiley said:
After 40,000 miles!

Really?
Yes, it's a relatively weak clutch-type LSD in a sealed unit and I think it's quite common for them to wear out after that kind of distance. No comparison to an aftermarket Quaife, ATB, Wavetrac, etc.

some random internet forum poster found via google said:
Clutch-packs can be destroyed in minutes if they're ill-suited to the application...like the OEM clutch pack in the R56 MINI Cooper S in the example I gave above. They don't "blow", the discs simply slip and turn it into an open-diff.

ch427

8,864 posts

232 months

Wednesday 1st July 2015
quotequote all
Last time i experienced it was worn suspension components as suggested, the bottom arms seem to be the most likely culprit.