Steering wobble?

[Adrian Southgate]

I have had the wheels balanced on the Sierra but I am still getting quite a wobble between 35 an 40 mph.

TCA ball joints seem fine, TRE's seem fine, bushes seem ok. Its not affected by braking as I have tried applying the brakes while holding the speed constant with the throttle so I'm ruling out disc balance and run out issues.

The only other thing I can think of is the play in the actual steering rack internals which I was advised about at the MOT.

Can I have your thoughts please gents?

[Big Vern]

Pressure is unlikely to cause steering wheel wobble and neither is geometry. Wobble is most likely attributed to wear or imbalance on something that rotates. If the wheel offset is much different to the original Ford then even a small out of balance on the wheel could affect this. (Aston V8 Vantage wheels are terrible for this, you wouldn't believe what 5grams felt like at 100mph.)

Thinking on what you have done, how good is the fit of your homemade triangular bit on the steering column? If there's any slack at all in the fit it could be allowing the wheels to shimmy. That would feel like wheel wobble.

[Adrian Southgate]

Wheels are huge but 0 offset.

I'll check the triangle joint as well while i'm playing with the rack.

I suspect it is a little toe in with play in the rack, I'll have to wait until its aligned properly to check that out.

[1xf87h8w80hlh]

i only ask about press as uneven press will cause probs. you allways start with the small things i have had all kind of probs discribed as wheel wobble from shit tyres,prop bearings,cab mounts to craine mountings anything that moves. when dealing with drivers you have to asume they know nothing.

[Pete Clayton]

I would expect if it was a geometry issue it would be pulling to one side rather than shaking the steering. Like BV says gotta be something that rotates, try swapping front and rear wheels over and see if it goes away

[Adrian Southgate]

I might try smaller escort sized wheels first, the backs on mine are 225/50/15 and are going to be a squeeze on the front :-)

[Dave Taylor]

Ade I have a brand new Mk3 Fiesta rack here, yours if you want it may need abit of a mod.

[Big Vern]

That'll be fun on the Sierra but remembering to turn the steering wheel right when you want to turn left could get tiresome :-)

[Adrian Southgate]

Thanks Dave but I have a spare rack in the boot of the black legerra, I've just got to get into the boot past that slimy 'orrible tarp :-(

[Adrian Southgate]

Well it got me home without overheating, possibly down to binning the thermostat as its doing just the opposite now :-( fine tuning is what it needs *he says grinning*

A more detailed description of the problem follows.

Potholes, manholes and other sharp deviations in the road surface cause the 'wobble'. You can drive through it now the wheels are balanced which I couldn't do before. It starts from 30 MPH upwards and is most pronounced at 38-40. It can be cured by turning the wheel slightly so the weight is transferred from one wheel to the other. It never happens going round roundabouts when all the weight is on one wheel. Changing direction coming off a roundabout is also wobble free. All this leads me to agree with Vern about the shimmy effect as it is as if the car can't make its mind up which way it wants to pull. There appears to be a 'dead zone' of about 5-10 degrees, something I should not have as I don't have any rubber joints in the steering system at all. I dont have any of these problems on the legerra and it has pretty much the same setup apart from the tops of the struts.

It is accompanied by a slight rattle from down the front somewhere so tonight's plan is to check the bearings again now its done a few miles, then change the wheels for 13" alloys that have been balanced to see if that cures it.

If this doesnt work then i'll put it back to the big wheels and change the rack.

[Big Vern]

Hmm,

If a deviation promotes wobble then either a front damper or since weighting the steering seems to deaden the wobble then I would say something is loose. Steering wheel, the triangulr joint, or rack pinion. If the rack itself was that bad then you must have Stevie wonder as your mot tester :-) The dead zone would suggest steering column and its associated would be a good place to start.

[Adrian Southgate]

Thing is with MOT's, they only test one item at a time and thats with a stationary vehicle.

Heres how I see it happening. If there is a slight amount of play in the rack (which there is) coupled with toe in and a small amount of play in the UJ. (also on the advisory list). The wheel hits the deviation in the road surface, deflecting it back into a 'straight ahead' position the other wheel will be pulling it back, when this wheel grips then it goes into the straight ahead position and the opposite reaction occurs. This then sets in motion a chain of events which gets worse until remedial action is taken (braking, turning or even hitting another deviation) I don't see this happening if the wheels are toe out as they will both pull outward in opposite directions. When you apply the brakes the front of the car will dip which will increase the toe out slightly allowing the car to regain its balance as the steering rack will increase in length in relation to the decreased angle thereby reducing the toe in.

I hope that theory makes sense to you guys as it seems possible in my head...

[Pete Clayton]

Sounds like tramlining to me