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Discussion Starter #1 (Edited)
Hi

What takes responsibility to absorb vibrations caused by pot holes? Even the smallest holes cause all car shaking. The dampers are good, there were checked on a platform, front wishbones (upper) are new, the back ones are good. Any hint?
Also question about chamber, I have noticed that back wheels have small positive camber, is that normal in 147? Or some suspension problem?

Greetings
 

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Weak dampers are known to cause the tremors through the car which is front the front suspension with its high unsprung weight oscillating. The springs are fairly firm so the bounce test does not really show it up.

AFAIK, the rear suspension should have around 1 degree of negative camber (out at the bottom and closer to the centre of the car at the top). Ride height adjusts the camber but the rear camber is less affected by ride height than the front suspension. The only thing which is adjustable on the rear is the toe settings. The other stuff is set and this is a first I have heard of it being wrong. If you are still sure it is wrong, have it measured or post some pictures of the car showing how the rear wheels sit and of the rear lateral arms.
 

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Discussion Starter #3
Didn't know that, thanks! I will check it then.

Oh god, I made a mistake in first post, I meant negative camber. If it is normal that I do not have nothing to worry about then. Thank you for reply!
 

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My 147 had a vibration / oscillation / judder in the front suspension, which was obviously a damper issue. New front dampers were fitted (Bilstein B6), and most of the 'judder' disappeared, but not completely, inexplcably some vestigial still remained. 'Inexplicable' because no other part of the suspension seemed to have a problem, at least I could not find one using the usual methods of testing ball joints and bushes for wear and tear.

Both upper control arms ('wishbones') were renewed when an upper ball joint failed, 'judder' was unaffected. The right side lower control arm was replaced when its' ball joint failed, judder unaffected. The left side LCA was left alone because there was nothing obvious wrong with it, i.e. the ball joint was tight and the bushes did not move excessively when pried heavily with a lever, seeming as stiff as the bushes in the near new LCA on the other side.

So with the judder was starting to get worse, the steering starting to feel vaguer, and the handling getting a bit weird (the car starting to 'self steer' in corners and under brakes), in the end I decided to replace the left side LCA depite there being no obvious issues with it, and as it was pretty much the only consumable front suspension part which had not been replaced since I bought the car. To my pleasant surprise, the judder disappeared, and the steering / handling sharpened up...

It turned out that the rear bush was on poor condition, which only became obvious when the LCA was off the car. With the rear bush housing held tightly in a vise, the arm could be substantially and easily wiggled excessively in all directions, far more than with a new LCA. But strangely this bush seemed OK while the arm was still fitted to the car, i.e. prising the arm with a big lever didn't cause a suspicious degree of bush deflection, seeming more or less similar to the bush on the much newer LCA as fitted on the other side of the car. Yet it wasn't OK...

I inspected this LCA bush on a number of occassions (pried with a long lever), and never found an obvious problem with it. This is despite being highly suspicious and really wanting / trying to find an issue with it (i.e. to find some explanation for a mysterious problem).

Regards,
John.
 

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Thinking out loud about LCA rear bush wear:

My cars' LCA bush judder / vibration / oscillation felt not disimilar to a dodgy damper. A bad damper obviously allows substantial vertical oscillation that is easily felt. A worn LCA rear bush would allow at least some relatively limited degree of horizontal oscillation. The loose rear LCA bush would oscillate laterally (in and out relative to car centreline), but because the bush is located well behind the axleline the wheel (etc) would not move laterally, but instead would move longitudinally (backward and forward).

Everything attached to the LCA would also move longitudinally, i.e. the hub, the axle, the brake, the suspension upright, the wheel, the tyre etc, all adding up to quite a lot of mass. As the rear bush dynamically flexes and oscillates, all that mass would tend to be in oscillatory longitudinal motion, so despite the degree of actual movement probably not being all that great, quite a bit of energy would be involved because there is a fair bit of mass in oscillation. This would explain why (with a worn rear LCA bush) significant judder / vibration can be felt through the steering and chassis, despite there being relatively little movement of the masses involved.

Of course a worn / loose rear LCA bush will affect geometry. As the wheel (etc etc) moves backward and forward the steered angle of the affected wheel will change to some degree, affecting directional stability because the one affected wheel is 'steering' in a slightly uncontrolled manner. Caster angle will also change with any longitudinal movement of the lower ball joint, probably affecting steering feel more than the actual handling (?).

The steering would be vaguer because some of the steering input (tie rod motion, and load) is not directly translated into the change in steered angle of the road wheel (or in consistency of steering force / resistance / feedback as felt by the driver). Instead, some proportion of the steering input that is moving the wheel etc longitudinally must be deducted from the change in steered angle of the road wheel, i.e. if a LCA rear bush is flexing excessively then for a given steered input the road wheel will steer less (it will also 'unsteer' less when the lateral input is reversed...). So, steering input is no longer only changing the angle of the road wheel, but is also moving it back and forth to a somewhat erratic degree, so the steering becomes vague(r) in both feel and effect. The steeing of the affected wheel has become erratically less linear...

As a consequence, (with a worn rear LCA bush) the steering may well behave and feel somewhat different in left vs right hand corners. Imagine looking at the car from above in plan view, and for purposes of this example lets imagine a car with zero *Ackermann effect and the worn rear bush being in the left side LCA. When we steer to the right the right hand wheel steers to X°, but since the left side wheel is attached to a LCA with a dodgy rear bush it doesn 't steer quite as much (i.e. X°-). The right side wheel steers a bit more than the left side wheel, so the car gains some steered toe-out.

Now if we steer the other way, to the left, the left side wheel still doesn't steer quite as much as the right side wheel, so if the right wheel steers to X° the left wheel still only steers to X°-. So when steering to the left, the left side wheel steers less than the right hand wheel does. So in this e.g. where there is a worn / loose rear bush on the left side LCA; the car gains some steered toe-in when steering to the left, but gains some steered toe-out when steered to the right. This is very likely to cause some degree of unequal steering feel and effect in left vs right hand corners...

Steering and handling stability is also affected because 'reverse forces' generated at the contact patch cause the worn bush to unpredictably flex, so causing uncontrolled changes in steered angle of the affected wheel.

* Of course 'Ackermann geometry' changes the 'steered toe' angle, adding toe-out with increasing steering input in either direction. So, if we add Ackeramann back into the above e.g. we find that when steered to the right our car (with the dodgy left side LCA rear bush) gains X° of steered toe-out, but when steered to the left it only gains X°- steered toe-out, so there would be less steered toe-out in left vs right hand corners.

This is 'in theory', but with loose compliances in bushes all sorts of unaccounted for changes in angles may occur. However, IMO it's quite predictable that whatever exact steering affects result from a worn LCA bush it is extremely likely to be unequal side to side, so the steering is still likely to be affected differently in left vs right hand corners, and so the car will most probably in some degree steer and handle differently in left vs right hand corners.

Regards,
John.
 
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