w108 Ackermann steering geometry

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L_O_O_M
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w108 Ackermann steering geometry

Post by L_O_O_M » Mon 24 Dec, 2012 2:21 am

Hi all

I was wondering if the w108 employs Ackermann steering geometry on the steering? :think:
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John Green
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Re: w108 Ackermann steering geometry

Post by John Green » Mon 24 Dec, 2012 7:42 am

Now there is a good question! Nearly all cars use aspects of the Ackermann principle to some extent, but very few (especially modern cars) use it as it was originally patented.

For those of you who have no idea what we are talking about:

http://en.wikipedia.org/wiki/Ackermann_ ... g_geometry
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Mercmad
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Re: w108 Ackermann steering geometry

Post by Mercmad » Mon 24 Dec, 2012 9:28 am

On the W108 ,yes it is. a line is drawn from the king pin center line,through the tie rod end center line to the center point of the diff. Both sides of the car ,if can imagine,have this line drawn so it forms a triangle . If a car is built without this simple geometry or modified so the centerlines intersect at a point other than the diff center,strange tire wear results.
"For road cars, zero toe or a small amount of toe in is preferred. Toe in enhances stability and self correcting tendency. Zero dynamic toe will also minimise tyre wear in a straight line. Most road cars will run a smaller percentage of Ackerman steering geometry to help slow speed steering maneuvers, but not allow dynamic toe out on higher speed corners on the highway."
For racing tech answers on this question read this...it gets really complex when you are considering speeds above 160kph.
http://www.smithees-racetech.com.au/ackerman.html

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Re: w108 Ackermann steering geometry

Post by L_O_O_M » Tue 25 Dec, 2012 2:57 am

How much different do you think the w108 will feel with a rack and pinion?Because on one of the other forums I am at one of the guy's said he has a 1st gen camaro and he will never go back to a steering box and linkage.I know a camaro is no MB.
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John Green
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Re: w108 Ackermann steering geometry

Post by John Green » Tue 25 Dec, 2012 10:06 pm

Now there is a discussion we have had before... There is nothing wrong with rack and pinion, infact MB changed over to it in the mid 90's. But how it is fitted is the trick. I would be more concerned with aspects of "bump steer" rather than adhearing to the Ackerman theory. I can't remember exactly what the issue is, but from memory the length of the control arm and the length of the tie rod have a relationship that needs to be correct to avoid bump steer and this is reportably difficult to achieve with a W108.

All that said if the car is being built for show or even GO, and not a a "drivers car" there are plenty of them out there that have had racks put in them. Like this one:

http://www.southsideengines.com/wild/in ... &Itemid=72
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Mercmad
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Re: w108 Ackermann steering geometry

Post by Mercmad » Wed 26 Dec, 2012 8:22 am

i have only seen ONE successful conversion to R&P steering on the W108 (etc ) chassic and this involved taking the front axle and turning back to front and then mounting a Mercedes power rack to the new front position . this was to enable the ackermann to be retained and allow the stub axle steeting arms to be connected plus get room to fit the rack under the car.
A lot of this nonsense about fitting R&P styeering to mercedes comes from those who are trying to use ideas gleaned from American websites where the GM and Ford cars are often converted to get rid of the crappy original steering.

To compare the pretty awful GM asteering box (in Australia see HQ holden) to mercedes power steering box is plain wrong... ha ha ha. There is nothing wrong with the mercedes steering box and as i mentioned before,if you can find a 6.3 box and idler arm you will be ahead of R&P because of the faster ratio.

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Re: w108 Ackermann steering geometry

Post by merc-304 » Thu 30 Aug, 2018 9:24 am

Came across this cool vid on rack conversion and bump steer

You Tube - Trevs Bedford CA van blog part 8 steering rack conversion / rack fitment and how he sorted his bump steer
Change the vid speed settings up a notch he does take his time explaining things....his other vids on panel work restorations are great also.
380 SEC

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John Green
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Re: w108 Ackermann steering geometry

Post by John Green » Fri 31 Aug, 2018 7:26 am

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