rear end like a bossy wife

[krisby]

My W203 C320 has been a bit "odd" since I got it, the handling has always felt wayward, lacking in confidence from the rear, especially as it was jumping and skipping over bumps when turning.
I took it in to my mechanic suspecting a broken spring or blown shock, and asked him to check all bushes and arms whilst under there (though there is absolutely no knocking so didn't expect any worn components). The rear suspension felt soft, but not bouncy, so I was not sure what to expect.

He said everything was fine, but the tires, especially the rear drivers side, needed replacing, and did agree the suspension was soft, but no weepage and no pogoing.

So, I fitted 2 new tyres, which made it feel a whole bunch better, but it still felt odd, like the back end was leading the front sometimes. This became quite apparent last weekend when I drove to Devon via the M3 and A303, but was especially apparent on the way back via the M5/M4, it was quite windy and at speeds a little shy of 3 digits the back felt again like it was pushing the front, like it was leaning over on one wheel and pushing it round, and it was particularly susceptible to cross winds.

I've done some googling and found another chap that described the same issue, but he'd just had his shocks and springs done a year previous, someone suggested the rear subframes but someone reckoned it wouldn't affect the handling that way, but tired suspension would, also said you would hear the knocking (which I never do, even at high speed).

In the end the chap had suspensions arms and bushes done, but as my guy has checked all these and nothing is awry, I am not sure where to go next. I am contemplating just trying the shocks seeing as we can get them at a reasonable price from ECP.

Anyone with experience of this willing to impart some brilliant advice?

 

[whitenemesis]

My S203 had similar handling characteristics at the rear until I swapped to coil-overs and dropped the ride height 20mm. Basically the MB suspension was far too strong on the rebound and would float the rear end on recovery from a mind turn bump. The Bilstein set-up I had fitted really absorbed the bump and released the energy in a much more controlled way

 

[markjay]

If you are near Chesham, go and see Tony Bones at Wheels in Motion. In fact, even if you are not near him, it is well worth the trip.

My W203 is Classic trim which means the car is high, softly-sprung, and has bulky 55 tyres. Which is how I want it, but some prefer the sure--footed handling of the lower Sport or Avangarde on low-profile tyres and stiffer suspension. Which one is yours?

In addition, my 1.8L M271 engine will be far lighter than yours, which may also explain in part why your rear seems a bit nervous.

Hope this helps.

 

[krisby]

My S203 had similar handling characteristics at the rear until I swapped to coil-overs and dropped the ride height 20mm. Basically the MB suspension was far too strong on the rebound and would float the rear end on recovery from a mind turn bump. The Bilstein set-up I had fitted really absorbed the bump and released the energy in a much more controlled way

Thats interesting to note, I had been thinking of Bilsteins or KYB for mine, thanks.

 

[krisby]

If you are near Chesham, go and see Tony Bones at Wheels in Motion. In fact, even if you are not near him, it is well worth the trip.

My W203 is Classic trim which means the car is high, softly-sprung, and has bulky 55 tyres. Which is how I want it, but some prefer the sure--footed handling of the lower Sport or Avangarde on low-profile tyres and stiffer suspension. Which one is yours?

In addition, my 1.8L M271 engine will be far lighter than yours, which may also explain in part why your rear seems a bit nervous.

Hope this helps.

Thanks, I might check them out, Chesham ain't too far away.
Mine is the Avantgarde on 17" AMG alloys, it already sits quite low at the back, certainly lower than the front, which is why perhaps it is just a case of it being soft and too fast a rebound.

 

[M271]

Sorted

 

[coolhand]

Sorted

What was it?

 

[DSM10000]

My C320 has just started feeling wayward as well, tyres are all OK (Michelin Primacy all around, 5mm rear,6mm front) new lower torque struts and alignment but still feels front heavy. I need to check the tyre pressures tomorrow as I have noticed that it is very sensitive to pressure.

After the front suspension work recently and tracking it felt much better, the only thing I know needs attention are the in-board rear anti-roll bar bushes, not sure how much these play in rear waywardness? The were only an advisory at the recent MOT but are being replaced next week anyway..

 

[krisby]

I had KYB Gas A Just rear shocks fitted yesterday, not sure if that is has cured the high speed shenanigans yet though, wasn't even sure it was the fix, but my guy said the old shock was compressible by hand, so even if not completely resolved the issue, I'm sure it will have contributed, afterall, it was still on the original 13 year old shock.

 

[Sp!ke]

Your shocks would have been compressible by hand when new from the factory.....

Should you not perhaps be getting a second opinion on cause of the problem?

 

[krisby]

not sure where to go though. It had the MOT in February, my mechanic has looked over the car twice, there is no rattling, nothing loose, and really the problems I had with handling are in extreme circumstances, i.e. when giving it some, but his point of view is there is nothing wrong with it, but if I wasn't happy to try new rear shocks seeing as that is where I can feel it leaning in, maybe I just need stiffer RARB.

I have no frame of reference though, so it might just be that is how C class drive.

 

[DSM10000]

not sure where to go though. It had the MOT in February, my mechanic has looked over the car twice, there is no rattling, nothing loose, and really the problems I had with handling are in extreme circumstances, i.e. when giving it some, but his point of view is there is nothing wrong with it, but if I wasn't happy to try new rear shocks seeing as that is where I can feel it leaning in, maybe I just need stiffer RARB.

I have no frame of reference though, so it might just be that is how C class drive.

Perhaps stop "giving it some" in "extreme circumstances"?

The C class is no sports car, it is set up to be softer and less sporting than the 3 series for example. It just is not the sort of car that responds well to being thrown about.

I find mine is fine if you plan ahead, set it up for corners and bends and it will make good progress but ultimately the rather slow steering response and comfort orientated suspension limits the handling.

If you stiffen up the rear anti roll bar without other changes that will have consequences for the handling as well., probably not good ones?

 

[krisby]

are you mental? no point having a 3.2V6 if I can't give it some.
Extreme circumstances wasn't necessarily meant at the same time, I mean odd road surfaces, eg near work, in fact outside QPR, there is a curve and part way round there is a crack in the road perpendicular to the direction of travel, even at 30mph this unsettles the car sideways, though I did notice tonight it was much better. There is also a big rut when I turn onto a main road and the car again used to shuffle sideways over this, but the new shocks have largely cured this now.
I know the merc isn't renowned for its handling prowess, that was never my point, but circumstances like above are abnormal even for a car built for comfort, in fact, with soft suspension I would have expected it to soak it up better than something more sporty like my previous BMW or ST220.
But I think it is better, it could possibly do with a stiffer ARB, but I'll leave it for now, I'm heading to cornwall first week of August, so will be a good test. That was largely the reason I had it done, factoring in the fact the family and luggage will be in the car, I wanted to know the shocks were up to it and the rear end would be more predictable.

 

[DSM10000]

are you mental? no point having a 3.2V6 if I can't give it some.
Extreme circumstances wasn't necessarily meant at the same time, I mean odd road surfaces, eg near work, in fact outside QPR, there is a curve and part way round there is a crack in the road perpendicular to the direction of travel, even at 30mph this unsettles the car sideways, though I did notice tonight it was much better. There is also a big rut when I turn onto a main road and the car again used to shuffle sideways over this, but the new shocks have largely cured this now.
I know the merc isn't renowned for its handling prowess, that was never my point, but circumstances like above are abnormal even for a car built for comfort, in fact, with soft suspension I would have expected it to soak it up better than something more sporty like my previous BMW or ST220.
But I think it is better, it could possibly do with a stiffer ARB, but I'll leave it for now, I'm heading to cornwall first week of August, so will be a good test. That was largely the reason I had it done, factoring in the fact the family and luggage will be in the car, I wanted to know the shocks were up to it and the rear end would be more predictable.

No I am not "mental" and frankly find your use of the word rather childish and offensive. You are the one using phrase like "give it some" and "extreme circumstances" without qualifying them so it was somewhat difficult to understand the road conditions you only now describe that unsettle the car .

As said, if you just stiffen up the rear ARB then you risk unbalancing the car

 

[krisby]

Oh come on, a bit of harmless jibing offends you? I appreciate your comments regarding suspension, but if that comment is offensive, I wish I had as little to worry about in my life as that.

 

[V12]

From your description, it sounds like you want to soften up the rear if anything.
Stiffer ARB on rear is asking for trouble IMO.

A C320 should be very comfortable at triple digit speeds in my experience.

Best thing to do is to take it to someone who really knows these cars otherwise you could end up throwing £££s at a problem that may not even exist. As you say, it may well be a character of the W203 that you are not familiar with.
Last time I had some dodgy handling characteristics on a W203 C220cdi, it was due to the rears having 5 psi too much in them. I couldn't believe how sensitive the setup was to the tyre pressures.

When diagnosing I would always go through the following in this order :
-Tyres
-Check Bushes / Joints for play
-Alignment (always by a reputable place, preferably a specialist that JUST does alignment)
-Shocks

 

[krisby]

Thanks for the reply, tyres checked and ok, bushes etc checked, twice. Admittedly alignment not done, but then it tracks straight and true, so I haven't gone there yet.
Shocks done as springs appeared fine and shocks were OEM and old enough to justify replacement
ARB is last resort though.

I'm not sure about softening it, the rear already feels soft, it is hard to describe, but it does feel like the old 70s Touring cars, Zakspeed Capri, when they would be leaning over on the back right wheel and the front left would be lifting. I'm not saying the Benz is doing that, its just the sensation that all the load is on that back wheel.
But anyway, it does feel better but I haven't had the opportunity to properly test yet, only boring old M4 commute this week.
The test will be Cornwall next weekend, if still showing signs of unexpected handling characteristics, then I might go for the full alignment on my return.

 

[DSM10000]

Thanks for the reply, tyres checked and ok, bushes etc checked, twice. Admittedly alignment not done, but then it tracks straight and true, so I haven't gone there yet.
Shocks done as springs appeared fine and shocks were OEM and old enough to justify replacement
ARB is last resort though.

I'm not sure about softening it, the rear already feels soft, it is hard to describe, but it does feel like the old 70s Touring cars, Zakspeed Capri, when they would be leaning over on the back right wheel and the front left would be lifting. I'm not saying the Benz is doing that, its just the sensation that all the load is on that back wheel.
But anyway, it does feel better but I haven't had the opportunity to properly test yet, only boring old M4 commute this week.
The test will be Cornwall next weekend, if still showing signs of unexpected handling characteristics, then I might go for the full alignment on my return.

I think stiffening the rear will just exacerbate this symptoms, look at an F1 car with a flat tyre, the chassis is so stiff it causes the car to lift a corner.

Pretty sure that having mismatched rear and front roll stiffness can cause lift off over-steer?

I do know what you mean about the car and the handling characteristics though, there are a number of roads around here where the car will feel slightly unsettled at fairly modest speeds when encountering a bump or poorly surfaced piece of road, it never slides or does anything dramatic but just has a momentary feeling of rear end lightness. I find that this behaviour is certainly lessened with passengers in the rear or when I have picked up 50Kg of coal in the winter.

Have you tried different tyre pressures front to rear? Mine (on Michelin Primacy all around) does respond better and shows less of this characteristic with the rears at 32 and the fronts at 34psi