Intermittent steering wobble?

[benczuk]

Hi all, I am after any ideas you may have as to the cause of the following.

I was towing my caravan back along the A30 at the weekend, flat-ish straight section, doing about 55, when all of a sudden the steering wheel started to wobble slightly.

I pulled over and checked the wheels, all appeared ok. So continued off again.

The wobble got more violent to the point where it didn't feel safe, experimentation showed that the wobble was only evident under load (accelerator depressed) and then only when in gear.

I pulled over again and this time turned the wheel from lock to lock to examine behind them. Again I couldn't see anything and as we were only 20 miles or so from home decided to continue gingerly on.

On setting off again the wobble had entirely vanished! For the remainder of the journey it behaved perfectly, as it had done for the prior 60 or so miles.

On arriving home I had both front wheels off (bolts were tight) and checked the wishbone mounts (new one recently fitted), drop links, track rod ends etc and could find no evidence of play anywhere...

Took it for a run out at speed again no evidence of a wobble... I'm due a 200 mile run to Southampton on Friday so any ideas of things to check welcome (no access to pp at the minute)

My thoughts extend to

* Air in power steering? (the pump has been making a slight noise for a while now)
* DMF stuck? (it again was only recently replaced, and vibration woudl have been throughout the car, not just the steering?)
* blocked injector??

[Welly]

The Caravan would have made the front end go light and exaggerate any wobbles but it sounds like the engine mount as this would be under extra strain when towing it could set up a wobble which is then felt through the steering.

[PeterN]

A steering wobble that comes and goes is usually due to both front wheels being slightly out of balance but going in and out of phase according to their relative positions, i.e. they will either add to the movement or cancel it out. When cornering the wheels rotate at different speeds so change their relative positions.

Peter

[benczuk]

Interesting idea Peter, when combined with the load on the rear...

Engine doesn't have any visable movement welly, haven't been under to check the bottom mounts though... may do that later today, but I would expect a failed mount to be a persistent wobble, not just appear for a mile or so then go away.

[Welly]

I thought you were saying it wobbles under load (acceleration)? with the Caravan on the engine mount will be under greater compression as the engine loads up the rubber mount it can transfer a vibration.

Peter's theory is good too.

So your steering wheel wobbles mainly? I wonder if you have a worn shocker up front, again the Caravan will exaser....eggsaser....excasser......Make it worse

[benczuk]

No, It only wobbled for that mile or so. Then stopped as soon as I had checked both sides for a second time, this time adding in a lock to lock on the steering to check behind the wheels.

Shocks are fine. When I dropped it back off the jack, no jelly wobbles, one bounce and stopped.

One of the front tyres is due a replacement. May go and get it swapped and check the balancing, if only it wasn't such a ball ache with these lovely center less rims.

[Doggy]

.... if only it wasn't such a ball ache with these lovely center less rims.

Amen to that. I think Peter's probably hit the nail on the head.

[benczuk]

Well, a new front tyre, 4 wheels balanced and 450 miles later, no return of the wobble. Bizarrely my fuel economy on the run home today was the best I have ever seen it get, 47.9mpg on the computer, It was at 50.5 for a section of the A303 The computer on a brim to brim test proved pretty accurate a while back, but I usually struggle to get above 43 so not sure what is going on there.

Now just have to fix the rear track arm which has developed a creek in the last week.. sigh.

Thanks all for the advice received.

[binnzy]

this may sound a bit stupid on a car but it happens a lot on wagon tyres with big deep treads, if you get a stone or something else stuck in the tread the steering wobbles and vibrates until the tyre sheds the offending item