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 All about: 2CV suspension 
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Agony Aunt - You have a car problem? Speak to Ken

Joined: March 6th, 2009, 1:40 am
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Post Re: All about: 2CV suspension
Geoff,
you do realise that the stops on the front arms are supposed to make regular contact with the rubber buffers?
The specified clearance between those parts is "between 3 & 6mm", which means that any downward movement of the front of the vehicle, or upward movement of an arm, greater than 20mm should bring the parts into contact.
If the clearance is set incorrectly, the front suspension will be adversely affected; too large a clearance and the suspension will be softer, too tight a clearance and the suspension will be harder, maybe even harsh.

If you examine the geometry of an A series suspension, the locations of the brackets which carry the knife edges are such that the front suspension has a constant rate, whereas the rear suspension has a rising rate.
The addition of those 'bump' stops makes the front suspension act with a rising rate.
Note that considerable stress is carried by the brackets on the chassis in normal use, something which has been underestimated by at least one chassis manufacturer...

Also, what's up with your droop stoops? When the vehicle is jacked clear of the ground, the droop stops should contact the rubber buffers on top of the chassis, or the chassis itself on LHD 2CVs.

Ride height is specified as 195mm to the underside of the chassis, at a point midway between the axle bolts.
Unless the vehicle is regularly used on rough roads, or across fields, I prefer to use a setting about 20mm lower.

ImageSetting front arm stops by slcchassis, on Flickr

Image2cv front suspension bump stop bracket on another brand of chassis. by slcchassis, on Flickr

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February 23rd, 2015, 8:58 pm
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Firing on two.
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Joined: November 25th, 2010, 6:02 am
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Location: Adelaide, South Australia
Post Re: All about: 2CV suspension
Thanks for the info Ken .. I really appreciate the help coming from the other side of the globe.
My interest in the front end (in particular) is because the suspension is already harsh, showing regular contact between the bump stop and rubber buffer.
And re the droop stops - just to clarify, if the (front) wheel is off the ground, the droop stops should just make contact with the buffer? I copy what you say, though, with respect to the bump stops playing a part in the suspension geometry: I just don't understand it!
It looks straight forward, but b_y well isn't!
The droop buffers show no sign of ever having made contact.
And to further test your patience, if I were to lower the vehicle by the 20mm you indicate, should that be applied to both front and rear? Or could I lower the rear only?
The car is only driven on sealed roads, and almost always with no rear seat passenger(s) btw.

Cheers, and good luck in the one day cricket!


February 23rd, 2015, 11:50 pm
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Agony Aunt - You have a car problem? Speak to Ken

Joined: March 6th, 2009, 1:40 am
Posts: 3611
Post Re: All about: 2CV suspension
Geoff,
as mentioned earlier, if everything in the suspension is set up correctly, there will be regular contact between the bump stop and the buffer mounted on the side of the chassis, even if you've only been on a shopping trip.
On the other hand, the only time that the droop stops would come into play whilst you're driving would be if you've managed to get the rig airborne over a sleeping policeman or a hump-backed bridge. ;)
Re. the droop stops when the front wheel is clear of the ground; the full weight of the suspension arm & road wheel should be supported on the droop stop.

A 'quick set' I use after a chassis swap or other work which affects the suspension; with one side of the car jacked up so that both wheels are clear of the ground, wind the rear tie rod into the shackle/tie rod end just enough to take up all of the free play. It should still be possible to move the tie rod end across the knife edge by hand.
For the front tie rod(s), wind them in until the free play is taken up, but then back them off about 5 or 6 turns.
That usually gets things fairly close, with only some fine tuning needed by checking the corner weights.

One day cricket? The ball is the wrong shape, much too round... :roll:


petitepoupée wrote:
Cheers, and good luck in the one day cricket!

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February 25th, 2015, 2:11 am
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Post Re: All about: 2CV suspension
Thanks yet again Ken ... it's so difficult, coming from conventional vehicles, for me to understand that what in a "normal" suspension system constitutes a travel limiter (ie a stop in the truest sense of the word) is, in the 2CV's, something that plays an integral part in the suspension's characteristics. I'll just have to accept it, eh :shock:
Checked the droop stops and they are doing their job - all the unsprung stuff is hanging free as it should - and no sleeping bobby required.

Can the rear be lowered, say by 20mm, while leaving the front as per factory recommendation? I understand that would require another check of the front settings, of course...


Last edited by petitepoupée on February 27th, 2015, 1:27 am, edited 1 time in total.



February 25th, 2015, 3:26 am
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Agony Aunt - You have a car problem? Speak to Ken

Joined: March 6th, 2009, 1:40 am
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Post Re: All about: 2CV suspension
Geoff,
don't forget about those rubber 'limit stops' at each of the suspension canisters, which play their part in the suspension setup of (most) A series models.
When the vehicle is lightly laden and standing still, the front limit stops carry a compressive load; when fully laden, that switches to the rear stops.
Of course, when in motion, dynamic loading means that this will constantly change depending on how smooth or bumpy the road surface may be...

Going back to your original comment about the (front?) suspension being too high, have you checked whether or not the front tie rods are still under tension when the wheels on one side are clear of the ground? If so, that can contribute to a harsh ride.

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February 25th, 2015, 11:33 am
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Post Re: All about: 2CV suspension
Oh dear ... back under the Duck yet again!
Might be a bit warm in the shed 'though - mid to high 30's (that's not Fahrenheit!) the next few days.
Will update when done.


February 26th, 2015, 1:22 am
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Post Re: All about: 2CV suspension
G'day Viking ...I somehow missed seeing your post - sorry about that.
Yes, our car is ex Mark McKibbin from Victoria, and it has done two raids, but I have it now set to correct heights front and rear. Tyres are now 4 new Michelin 125's.
I think I am learning a LOT about 2CV suspension - and am grateful for the patience shown by les amis who know so much more than me!


February 26th, 2015, 1:36 am
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Post Re: All about: 2CV suspension
Hallo Ken,

Are these tie rod supposed to be tight or loose, when jack up?

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February 26th, 2015, 11:55 am
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Post Re: All about: 2CV suspension
They wiII move when not under load from the suspension :-)


February 26th, 2015, 2:04 pm
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Post Re: All about: 2CV suspension
(Thanks banjo- I didn't do my reading)

This may help:
Please note tyre and type diversification.

Ken,
After lowering by 20mm, do you adjust the bump stop shims or not?


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February 27th, 2015, 11:30 am
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