Lotus Elan

S4 Front Springs - Part 2

PostPost by: AHM » Thu Aug 08, 2013 12:35 am

Ok. With New springs I set to fix this problem lotus-suspension-f42/front-springs-t23547.html, only to discover that the new standard springs were exactly the same as the old ones.

Lots of further reading dug up this thread lotus-suspension-f42/front-suspension-woes-t21434.html

I got the tape measure out and measured 2" from the centre of the bottom mounting to the spring seat. I'm guessing that the standard Armstrong seat was about an inch for the same measurement.

I've also read that the ratio of spring/damper travel to wheel travel is about 1.8 times so that extra inch is what is giving me (and I suspect a lot of other people) too much height at the front.

Are standard Dampers available ? I don't want adjustable anything, and from the pictures I have seen new dampers all seem to have a damping adjustment screw where the spring seat needs to be.
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PostPost by: UAB807F » Thu Aug 08, 2013 5:38 am

I've also been through a similar process regarding what I've always thought were OEM front springs/dampers. My S3 seemed a touch higher at the front, but as everything was supposedly standard I'd always assumed it was right, my perception was wrong and it all settled down when being driven.

Since changing the suspension I was forced to think about what I was doing rather than my usual trait of just bolting new bits on and driving the car, got confused and started this thread which had some helpful comments along the way;

http://www.lotuselan.net/forums/lotus-suspension-f42/suspension-ride-height-t28968.html

There's a reference halfway down to a workshop manual page which gives dimensions for the dampers unladen/laden and shows horizontal wishbones (Section C, page 5). I think this is better than measuring the spring platform height as it fixes the static dimension of the complete unit and this is what's going to affect the radius of movement at the wheel.

I was fitting Kelvedon suspension front & rear so I rang Pat Thomas one Saturday morning and he was very helpful. His comment was that the wishbones should be very, very slightly downwards from horizontal but he would do this only by setting corner weights. As I haven't the kit to do that, I ended up setting the arms horizontal using the inner & outer bolt centers as a second best option.

The car now rides amazingly and I could kick myself for missing out all these years. Also for the first time ever I didn't have to struggle to refit the a/roll bar, another clue that something wasn't right before.

My conclusion was that when I bought OEM parts in good faith years ago, what I got wasn't what Lotus originally specified. Based on my findings I think I'd start off by looking at wishbone and wheel camber angles with your new springs. (there's a cheap Gunson wheel camber angle device or you can get a good idea from a basic spirit level)

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PostPost by: AHM » Thu Aug 08, 2013 9:04 am

Brian,

Thank you for your comments

I'm coming at this, having recently fitted (thanks to the generosity of a forum member) a second hand pair of OE dampers and springs to the S3. An epiphany! ..... So that is what the ride is supposed to be like!

15 years ago, when I first had the S4 I was a graduate trainee at a large automotive component manufacturer. Working in their UK R&D centre I used to take it into the workshop after work - The Director of vehicle testing was an ex-S2 owner. One lunch time he spared me 5 minutes and drove the elan - his conclusion was that the springs and dampers were not right. I adjusted the dampers but could do nothing with the springs which gave the nose-up attitude - hence my conclusion that the spring rate was too high - even though the receipt from a well known supplier showed that they were standard.

Having compared the OE part with what well respected 'Specialist' Suppliers are selling, and having endured so many years of sub-standard handling I believe the answer is to get the OE set-up.


UAB807F wrote:I think this is better than measuring the spring platform height as it fixes the static dimension of the complete unit and this is what's going to affect the radius of movement at the wheel.


I disagree - The spring platform sets the 'height' of the suspension - Those measurements rely on the position of the spring platform being in the correct position - if you change its position you have to change the length of the spring or its rate. Which will mean that you do not get the characteristics that the designer intended.
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PostPost by: MyLotus » Sun Aug 11, 2013 12:18 pm

I am new to the Elan and I find the ride quite stiff. I am having a hard time finding out how to identify the type of suspension springs ans shocks installed on the car by the previous owner when he restored the car. Is there a way to identify the type of spring by measuring coil diameter for exemple?
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PostPost by: oldelanman » Sun Aug 11, 2013 12:42 pm

Don't know if this helps or not but the workshop manual has data for the standard springs......

FRONT
No of coils 19.6
Wire dia 0.324"
Rate 75 lb/in
Free length 16.08"
Fitted length 9.22"

Longer springs were also available to increase front ride height:-
Free length 16.75"
Fitted length 9.86"
(Pt No 26C 010A)

REAR
No of coils 8.7
Wire dia 0.4"
Rate 67.5 lb/in
Free length 14.71"
Fitted length 8.0"
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PostPost by: MyLotus » Mon Aug 12, 2013 11:29 pm

Thanks Roger. I have measured the front springs and mine are 9.86 in length (fitted), 22 coils. Wire diameter is .324 in which is (according to the manual) the same spring fitted to the Sprint. Now, why is it that the front end of the car is so stiff? When I raise the front, there is practically no droop on either side and when I lower it the suspension does not move... Does longer spring mean higher spring rate? I don't think so. Also checked the shocks to see if they are seized: placed one front tire on a block; the spring and shock do compress. So, the suspension is free to move. So, why is it that the suspension does not compress when the car is lowered on the floor? Help!
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PostPost by: UAB807F » Tue Aug 13, 2013 5:55 am

Hi,

I wouldn't have expected a longer spring to have a different rating in terms of lbs/inch, the extra length will just give it a bit extra height when installed on the same damper as a shorter spring of the same rating.

When you say the suspension "doesn't move", is this when it's first lowered to the ground after being raised under the front chassis ?

My (supposedly) OEM suspension behaved as you describe but would settle down when you rolled the car backwards/forwards to allow the wheel camber to return to normal. It never managed to get the lower wishbones horizontal even with someone in the car, but I did notice approximately 1cm difference in ground clearance under the chassis when my wife sat in.

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PostPost by: MyLotus » Tue Aug 13, 2013 1:55 pm

Thanks Brian,

I tried your suggestion: moving the car after lowering the front end to allow for camber adjustment. No noticeable compression of the suspension. As if it was already under load... Made sure the shocks are not seized by placing one front wheel at a time on a block and lowering the car: the suspension does compress. As far as I can see, two possible reasons for the suspension not to compress as it should when the car is lowered. 1. The shocks are not compatible with the taller springs; ie. the shocks are at maximum opening with the car resting on its front suspension and the springs are therefore already too compressed. Therefore, the suspension will compress under extra heavy load but not in normal driving. 2. The shocks are gas filled which makes them extra hard to compress.
Your thoughts and suggestions will be most appreciated.
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PostPost by: oldelanman » Tue Aug 13, 2013 2:19 pm

Another possibility - if you have the standard bonded rubber wishbone bushes. The suspension hardware should be torqued up with the suspension at normal ride height, ie with the car on the ground. If the hardware has been torqued with the suspension hanging the car will not settle to the correct ride height and the suspension will be stiffer as you are trying to wind up the rubber bush more than it is designed for.

Try slackening all the hardware and retorqueing with the car on the ground.
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PostPost by: rgh0 » Tue Aug 13, 2013 2:24 pm

If the spring free length is to long you will have higher preload when the spring is fitted to the shock. The preload could be such that the weight of the car is insufficient to overcome it and further compress the spring. Have you taken a spring off the shocker and measured it free length compared to the manual specification. Is the installed length at full droop the same as shown in the manual also? If the shock has a smaller installed length at full droop this will also give a greater preload.

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PostPost by: billwill » Tue Aug 13, 2013 3:36 pm

oldelanman wrote:Another possibility - if you have the standard bonded rubber wishbone bushes. The suspension hardware should be torqued up with the suspension at normal ride height, ie with the car on the ground. If the hardware has been torqued with the suspension hanging the car will not settle to the correct ride height and the suspension will be stiffer as you are trying to wind up the rubber bush more than it is designed for.

Try slackening all the hardware and retorqueing with the car on the ground.


This is of course difficult to do as you cannot get under the car to tighten the nuts, when it is at normal ride height and the lower arms horizontal, so you either need it on a 4 post lift or drive it onto two wheel ramps then jack up the rear and shove two more wheel ramps under the back wheels.

It will be quite close to OK though if you just have the two front wheels on ramps and the rear wheels on the ground.
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PostPost by: oldelanman » Tue Aug 13, 2013 4:21 pm

billwill wrote:
oldelanman wrote:Another possibility - if you have the standard bonded rubber wishbone bushes. The suspension hardware should be torqued up with the suspension at normal ride height, ie with the car on the ground. If the hardware has been torqued with the suspension hanging the car will not settle to the correct ride height and the suspension will be stiffer as you are trying to wind up the rubber bush more than it is designed for.

Try slackening all the hardware and retorqueing with the car on the ground.


This is of course difficult to do as you cannot get under the car to tighten the nuts, when it is at normal ride height and the lower arms horizontal, so you either need it on a 4 post lift or drive it onto two wheel ramps then jack up the rear and shove two more wheel ramps under the back wheels.

It will be quite close to OK though if you just have the two front wheels on ramps and the rear wheels on the ground.
.


Here's how I did it....Chassis level on stands front and rear then jack up hub until the wishbones are horizontal.
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PostPost by: MyLotus » Tue Aug 13, 2013 5:42 pm

The latest...

I slacked and retorqued front suspension hardware, as suggested, with front wheels on ramps. No difference. THen I measured droop length: 13.5 in (as specified in manual). Then I measured same length with car on ground: only barely 1/8th lower...
Here's a pic of the car on the ground. As you can see, the lower arm is angled, suggesting a too tall spring. As Rohan suggests, the extended shock is not long enough therefore giving the spring a greater preload than normal. Another way of putting it: the shock is OK (as indicated by droop length) but the spring is too long. A shorter spring would also level out the lower wishbone. Right?

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PostPost by: UAB807F » Tue Aug 13, 2013 9:45 pm

That picture is remarkably like mine was with the OEM setup in unladen state, does yours get any better if you get someone to sit in the car ? If not, then there's clearly something amiss because the manual indicates there should be roughly 1.7" between droop & normal ride. Mine never made the correct laden dimensions but it did move more than 1/8".

Quite honestly I've no idea what's wrong, my first thoughts would be centered around the spring, either too long as you suggest or it's too high a rating but in the standard free length.

Or possibly a damper problem as referenced previously in the thread, the spring platform being welded too high up on the damper body. I suppose the latter could happen if someone decided to use a different spec damper which just happened to have the same overall dimensions and movement range ?
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PostPost by: MyLotus » Wed Aug 14, 2013 1:32 am

My wife (130 lb) sat in the car while I watched the front suspension. No movement at all! As for the spring perch, it is placed very low on the damper, not possible any lower. So we're back to the spring: most probably too long, producing excess proload. I guess the next step is to remove the front springs and measure free length. Appreciate all the advice. Will keep you posted.
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