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Steering Wobble and "The Weekend Problem"


SPendrey
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My Disco has a worrying habit of wobbling like the wheels are terribly balanced, just after 45mph.  I searched online and came up with a lot of probable causes...

  • Wheel balancing
  • Steering damper
  • Bushes
  • Swivel preload

Along with these ideas, there were just as many people saying "it can't be the damper/bushes/swivels" and so on.  So I figured I'd get on with finding out for myself.

First was the swivels, mainly because I'd already replaced one about a year ago, so I check the preload and the new (ish) one is fine, the other has none at all.  Great, that'll be the culprit then?  No.

Next did all the bushes, which was a PITA but doable.  No difference.

The wheels didn't need balancing, and the wobble was there with two different sets anyway.  So what's left?  Well, the steering box itself has a leak and a little play in it.  Out comes the credit card and not long after arrives a refurb'd steering box.  I know, I searched, lots of "only buy new", "refurbs never work" etc.  Anyway, before I got to that, I figured I had nothing to lose by replacing the steering damper as I had a spare (new) unit sat in the garage.  Hey presto, wobble is almost gone.  My suspicion is that the steering box is toast, and the old damper had no resisting effect so the wobble was pronounced.  The new damper is, well, dampening the wobble to a huge extent, but the box still needs replacing.

So, started on Saturday afternoon, got the old box out fairly easily (and noted a front bearing needs doing to), only to find I can not shift the drop arm.  Ordered a replacement drop arm, but have to wait until Tuesday for it to arrive - that's "The Weekend Problem".  I now vow to start any jobs on Wednesdays.

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My experience with "death wobble" on a 110 is that it never just one thing! There are usually a number of culprits causing the problem and an equal number of mitigations that prevent/reduce it! 

Loose swivels are a favourite cause, panhard bushes and steering dampers (in my experience) are the prime mitigations. 

Once you lose the benefit of new bushes or the damper is less efficient, the death wobble will return! In the end I fitted a sprung damper and that solved it!

Good luck with the steering box! I used to remove a few bolts from the top (to give me access) and I had a Snap On track rod end bush splitter and a bl00dy great lump hammer.  It would come eventually!

Cheers

Peter

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Here's the latest, and I'd like opinions on weird symptoms please...

Fitted new (recon) box with new drop arm on it.  It was a Britpart drop arm so had to clean out the lumps of paint from the splines before fitting :-(  Replaced the lower steering UJ with a Bearmach one too.

From outside the car, the wheels are much harder to push left/right, but from inside the steering is REALLY light, and doesn't self centre.  Is this something that'll come back with a little use while the box 'loosens up' or something like that?

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Did you change the wheel alignment at all?

it's natural for a well aligned steering system to want to come back to straight (unless its lego) so there must be a physical problem stopping it doing so.

Are the drop links properly tight, there might be some play on the cones, they have to be just right or they will wobble all over the place and potentially lock too

 

(edit) could be the drive shaft bearings between teh most wobbles at specific speeds are bearing related. if its further in than the wheel bearings it will probably need the cv's doing as well

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There are different ratio steering boxes, so that may explain why there is a change in the external resistance to pushing the wheels, then again, that could be the steering damper.  The lighter feel on the steering wheel could just be that the old unit had internal leaks and the hydraulic assistance was reduced, or it could be that the valve porting in the new box is to the lighter feel specification (that is also another option).  It should, however, self centre normally when driving irrespective of the steering ratio or hyd pressure options.  It could also be a sign of an overly stiff damper or tight swivel preload, but that seems unlikely.  Do you have a suspension lift with standard radius arms, wheel spacers or non standard wheels?

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I do have a 40-50mm lift on the front... but then it's been there for 2 years without issue, and was the same springs etc. used on the previous car for 6 years without issue.  Seems odd to present itself as a problem now?!

There were no changes to alignment etc., except for undoing the drop arm/drag link ball joint, then doing it back up again.

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A lift without corrected radius arms or bushes removes the 3 degree castor angle from the swivel pin orientation and that is what gives the self centring, not the steering box or damper.  The stiffer external resistance on the steering mechanism, almost certainly from the new damper that replaced the failed one, is overcoming the weakened self-centre forces of your steering geometry.  Te fight between the weak self centring force and the increased damper force holding the steering in the last input position is the likely cause of the wobble.  It was the failed steering damper that previously hid your geometry problem.  Fit castor corrected radius arms or the correcting bushes at the axle ends of the standard arms and I'll bet your problems will go away.

 

However, you mentioned that the steering box was a refurbished one, not new, and you are aware of previous debates on that.  It could also be a factor.  If there is no discernible play in the box, which I assume you checked for, then my money is on the castor issue.

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