c350 cdi steering pulling left - problem solved

billbill

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:D

Have lived with my c350 cdi for a few months now and am really loving the car. The engine is great and the added pleasure it brings both aurally and in terms of power soon makes me forget about any loss in mpg over a 2l.

The ride ( adjustable dampers and 18's) is the perfect combination of body control and comfort and far superior to my b7 a4. I very rarely use the sport button, only to get the gearbox into first at a junction or traffic lights;)

But despite all of this and enjoying the Harman kardon stereo (logic 7 processing really helps the sound), the panoramic roof and other extras, I found the whole experience tainted by the steering pulling left. Having been told by my very well thought of MB independent that there was no problem, I took the car to Wheels in motion in Chesham. An hour and a half later and the car is transformed. So much nicer to drive especially on longer journeys. I would recommend to anyone.

Thanks, Bill

Ab
 
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billbill

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Hi, yes was given a printout with lots of numbers on it. I'm not very technical myself, so don't understand it but can obviously see there has been some change. Are you interested in it? Will attempt to upload later if so. Really has made the car so much nicer to drive.
 

Dieselman

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I'm interested to see whether the car was out of spec to start with and whether adjustments have kept it within spec.
 
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billbill

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Hi, will try and attach a photo of printout. Recall the chap saying the car was within spec to start with, as expected. Not sure what it is now.

DSC06209.jpg
 

Meldrew2

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Manufacturer's spec can be a bit over tolerant sometimes - otherwise a lot of stuff straight out of the factory would be out of tolerances.

There's a pretty big band of "acceptable" but a much narrower band of "ideal". Glad you got it sorted.
 

Dieselman

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Manufacturer's spec can be a bit over tolerant sometimes - otherwise a lot of stuff straight out of the factory would be out of tolerances.

There's a pretty big band of "acceptable" but a much narrower band of "ideal". Glad you got it sorted.
Looking at the sheet some adjustments are out of tolerance and some right on the edge. The rear axle has a bias to send the car left, so the front castor has been set out of tolerance to send the car right.
I wouldn't accept that.


The factory get it right because they do it like this.

http://youtu.be/CLXZX15JOmM?t=4m
 
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billbill

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Car is a Sport.

Agreed, out of tolerance slightly.

Are my wheels going to fall off?
 

Dieselman

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I wondered because the camber is right on the edge of tolerance, but the car selection isn't Sport suspension, which will make the negative camber greater.

Agreed, out of tolerance slightly.

Are my wheels going to fall off?
No, but it's not ideal. The front setup is compensating for the rear not being true.
 

wheels-inmotion

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The end castor positions are deliberate.... Castor has many duties the main one is directional stability. If the castor positions are staggered toward the right then the inert energy can belay the effect of the road crowns bias to the left.

The MB tolerances are very small so in order to belay the historic drift left we have to violate the "suggested" MB datum and it's for this reason MB cannot stop the pull left because they cannot move outside of the datum.

The "cross castor" which is now in red is a warning the car will/ could pull right. Again the tolerance disparity between the front castors is very small so again we need to violate the tolerance.

If we used the powerful energy generated by the camber then it would be easier but open to the fact tyre wear could become an issue. You will not get tyre wear from a castor stagger unless it was a few degrees outside of the suggested datum.

It could be argued the car will pull right on a flat road or in the EU, well i don't deny that but it's hobsons choice. The customers complaint is pulling left, telling me what type of environment the car is mostly driven.

I keep saying "suggested datum". Reason for this is the datum offered is simply that "suggested", it is not the law and cannot cover everyone's driving enviroment, style and so on. So within reason if the problem is geometric ( not mechanical ) then using the angles different forces outside of MB's suggestion is wise.

A few points i would like to add...
: The reason MB's tolerances are so small is the build quality is so superb. They don't allow large tolerances because in their opinion it will not be needed.

: Other manufactures do get it wrong? Over years i've had to write new solutions for the likes of BMW, Mazda, Lexus, Honda and so on.

: The MB's near perfect symmetrical build is it's nemesis not because it's bad but it's perfection cannot cope with the UK's road crown, so what to do? Flatten all the roads or inertly dial in a geometric compensation for the road crown.
 
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billbill

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Morning, thanks for the reply.

Agreed, the cross caster is 8 minutes/less than a seventh of a degree over what is already a tight tolerance.

The car is now pulling pretty much dead straight and is perfect for the UK roads on which I do all of my driving.

Again, I am very happy with the work that has been done and if anyone with a sore wrist is considering it, I would recommend it unreservedly
 

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