[W126 Coupe] Do I have suspension problems? (shuddering/instability over rougher roads)

[Dawid Loubser]

Hello,

I recently took the 560SEC on a 3500km round trip (Johannesburg to  
the Cape, and back) and I
experienced some weird behaviour. Over smooth, high-quality highway  
the riding quality and
stability is fantastic as ever, but over non-ideal sections (worn  
road, and little bumps
e.g. when going over a bridge at 120km/h) the car felt incredibly  
"loose" and uncontrolled.

Furthermore, if I hit a small bump, I feel shuddering through the  
steering wheel that goes on
for quite some time after the bump is over... The bump doesn't feel  
damped at all. The
one time there were several small indentations on the road, and the  
steering wheel shuddered
so violently I stopped to check if my wheel was falling off.

Yet, now that I'm back in Johannesburg, over smooth roads the car  
drives fantastically.
I'm only back now, and intend to start the investigative process -  
but any guidelines
would be fantastic.

My car (1990 model) is just about to go for its 120,000km (major)  
service, so anything I can
point out to my mechanic would be great.

My wheels, tyres and shock absorbers are fine, so it's highly  
unlikely that they're the
problem. Tyre wear on the front also seems normal. I've had my car  
for 30,000km now, and
I think this problem slowly got progressively worsen (from my memory  
of driving the
car on different roads) - I've never done a long trip like that  
before though.

thanks ever so much,
Dawid