Low speed wobble, high speed vibration

[jazzdude]

I am experiencing a shake / wobble over smooth surfaces as if a wheel is bouncing over a rough surface at speeds up to about 35-40 mph, in my W124 cab. I can feel it both in the steering wheel and the rest of the car (eg, if I touch the door or a seat, you can feel the vibration).

On the motorway, there is a slight vibration but not as bad, again in both steering wheel and car.

I have had the wheels balanced, and the front and back wheels tracked recently. I went back to the place that carried it out and they implied that it could be my tyres. The front tyres are new 2012 continentals, the rear 25% worn continentals, although they have a 2005 date on them. The car has not been used very much this last year as it was in storage and then on a forecourt before I bought it.

Even though the wheels have just been balanced, using a Hunter 9000 (which I understand is a good machine) and they did not seem to be warped should I ask them to balance them again or could there be another reason?

 

[trapperjohn]

Totally wrong maybe but I wonder if you have "flat spots" on your tyres (perhaps the rears) if as you say the car has been stood.

Perhaps also have a look at the ARB's at the front.

 

[WDB124066]

Apart from wheels and tyres the other main contributing factor to this in my experience are the suspension bushes - all of them.
How many miles has the car done and what has been replaced rubber-wise up front...??

 

[MD5]

Along with the above, have a look at the steering damper, which is a shock absorber that links the left and right steering assembly. Simple diy job, with one bolt on either side, and approximately a £40 odd part.

 

[jazzdude]

The car has been inspected on a ramp and has passed both a UK MOT and one here in Cyprus when it got here. The bushes were also checked and I am told that they all seem to be fine.

We had the engine mounts replaced in the UK before it was shipped here.

The car has just turned 100k miles.

The steering damper has come up in a couple of threads I read, but would that have an effect on the whole car vibrating at low speed?

Just to clarify, the car isn't shaking violently, but at 15-40 mph it just feels like I am driving down a road with a rippled surface, even though the road is smooth. It's like the wheels are bouncing up and down on a broken surface, but it goes away as I speed up and is replaced by a small vibration at around 70mph.

 

[WDB124066]

I see. Suspension bushes can be hard to inspect properly. My top strut mount had a crack 2" long and it looked fine on the car!

ARB bushes also made a big difference. Problem is unless you replace all of the front rubber it's hard to get rid of the wobble, I know exactly what you mean, but with new suspension there is no wobble, they are smooth as silk.

Are you in North Cyprus by any chance...??

 

[MD5]

The damper is telescopic, so you can check to see if it is weeping, but I have replaced three over the years on different cars with similar symptoms, and it's common with the 129 SL also.

 

[jazzdude]

What would be the best way about going about this without replacing everything? Is there a way to do it in a logical way as replacing ALL the bushes, suspension etc could be a money pit.

I know bushes suffer when a car is not used, but where would be the best place to start?

We are in the south.

 

[WDB124066]

It may not be too bad, ARB bushes, top strut mounts, and LCA bushes are a good start, should make quite a bit of difference together with a steering damper.

But make sure the wheel balance is correct first...!

 

[jazzdude]

I took the car for a second opinion today and the tech said he felt the bushes were all fine, the steering had no evidence of needing a damper and felt it might be the tyres.

Funny thing was that at the time he drove it the vibration was less pronounced and it got me wondering whether the fact it was late afternoon that the tyres had warmed up hence the smoother ride.

The fronts are brand new but the rears are from 2005 and the car stood for a while.

Does that make sense?

 

[jazzdude]

I took the car for a second opinion today and the tech said he felt the bushes were all fine, the steering had no evidence of needing a damper and felt it might be the tyres.

Funny thing was that at the time he drove it the vibration was less pronounced and it got me wondering whether the fact it was late afternoon that the tyres had warmed up hence the smoother ride.

The fronts are brand new but the rears are from 2005 and the car stood for a while.

Does that make sense?

 

[trapperjohn]

Hmmm. Rear tyres coming up 8 years old and stood for a while.

Would it be worth putting your spare on one of the rears to see if the vibe is less. Or even swop the fronts to the back for a while to see if that makes any difference.

 

[Ian B Walker]

How about checking the gearbox mounting. This would cause vibration if it was worn.

 

[stwat]

I had this exact problem. It turned out to be an out of shape tyre on the front.

 

[jazzdude]

It seems the tyres are the main suspects, with a stronger bias towards the 8 year old rears.

My worry is that I go and get the rears changed only to find that the problem was with the front tyres, even though they are new.

The spare looks like it came with the car and is unused, although probably 20 years old, so needs to be changed anyway.

 

[kth286]

can you borrow a couple of wheels from a garage for half hour to see the effect ?

The steering damper is literally one bolt to undo, and then push it in and out
whilst the other end is still atttached.

If it is easy to push in/out, then it needs to be replaced.

 

[WDB124066]

You could try letting your tyre pressures down a bit. MB recommend 30 psi in the front for a Cabriolet. I think 34 is about right but you can drop them to 30 psi for a while to see if the wobble goes away or changes...

 

[jazzdude]

Letting the pressure down from 34 to 30 psi made a difference, it was the first thing I tried.

Apart from getting under the car and pulling the damper out, is there anything in the way the car steers that would point you to a failed damper?

 

[kth286]

Letting the pressure down from 34 to 30 psi made a difference, it was the first thing I tried.

Apart from getting under the car and pulling the damper out, is there anything in the way the car steers that would point you to a failed damper?

You would get a shake/wobble via your steering wheel as you describe.

It more important for the damper to be good on the cabs with no roof.

 

[WDB124066]

Is this the wobble that goes away at 60 mph...?