How tired is my suspension?

[Uncle Fester]

C220 estate, 2001, 148k on the odo.

Driving on the north eastern clockwise section of the M25 last week at around 80mph with cruise on, and as I came round a long right hand bend there was a "step" in the carrageway, much like you get on bridges and overpasses.

The whole car "skipped" to the left by about a foot, which took me quite by surprise.
Now to me that says the shocks are tired, and at the mileage I wouldn't be surprised, but, they show no signs of leakage, and under most "normal" driving coditions appear to behave ok.

Is this normal behavior for a 1.5 ton estate? or am I expecting too much?

what is your advice?
are standard shocks an expensive job?
can a (reasonably competant) DIYer replace them easily?
Are there better after market shocks ?

 

[Sp!ke]

I would be looking closely at the tyres for uneven wear. Perhaps your tracking is out... hit any potholes recently?

 

[Uncle Fester]

only had the car a week and a half, the tyres look good, with no signs of uneven wear and the balance is ok.

The steering wheel is a little off centre (to the left) which make me suspect the tracking could be a little out.

The rear end feels worse than the front (slightly)

And.... who hasn't hit pot holes recently???

I have reciepts that say three lower suspension arms were replaced in 2009 (why not all four?) presumably as cheaper than doing the bushes?