Slight shuddering from steering at low speed

[mgarvey]

Last week I was test driving the 1997 SGL5 diesel Bongo I'm about to buy and I noticed something that worried me and I've asked the dealer to look at. The dealer is a very reputable and well known one on here, I've told them in writing and I'm sure they'll sort it, but I wondered if the symptoms are recognisable to others.

I was driving the Bongo on a very slow and bumpy gravel drive and felt a kind of shudder and clonk through the steering when going over bumps, as if the wheels were moving from side to side but the steering wheel wasn't. My first thought was a steering rack problem, but in the remainder of the drive I tried to replicate the fault on the road and couldn't; there was no apparent play or looseness in the steering.

The current tyres are a winter tread/compound and 195 section all round, which will be replaced by the proper sizes before we take delivery, but I'm not sure this alone would cause the symptom unless they've been like that for ages and caused a diff problem.

This leads me to wonder whether there is a problem with the suspension or bushes or something? The van has apparently just passed it's MOT test so presumably there isn't sufficient wheel or steering movement for it to fail.

Any ideas? I've done a quick search on here and couldn't find something obviously similar.