Lotus Elan

Oval rear control arms

PostPost by: Quart Meg Miles » Mon Dec 31, 2012 11:42 am

Does anyone know, or can they measure, the elasticity of fitted newish rubber bushes, old ones that Gary has soaked in oil for forty years and modern poly?uro versions? Answers in lb/inch or kg/mm please or whatever.

My interest is the distortion they suffer from the torque of the wheel under hard acceleration and even harder braking, both of which will affect the toe-in/out. I once detected a failed rear wheel bearing, and knew which side, by the car's directional change under and off power.
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PostPost by: garyeanderson » Mon Dec 31, 2012 12:29 pm

Quart Meg Miles wrote:Does anyone know, or can they measure, the elasticity of fitted newish rubber bushes, old ones that Gary has soaked in oil for forty years and modern poly?uro versions? Answers in lb/inch or kg/mm please or whatever.

My interest is the distortion they suffer from the torque of the wheel under hard acceleration and even harder braking, both of which will affect the toe-in/out. I once detected a failed rear wheel bearing, and knew which side, by the car's directional change under and off power.



http://www.google.com/search?q=rubber+d ... ydDIV0Y2VI

There are durometers for testing the hardness of rubber, urethane and the like. I don't think that they will measure "creep" or the permanent movement (deformation?) of the rubber. My guess it it's likely better (cheaper?) to just replace the bushes (about 4 hours and you should be cleaning up). Lee's Spyder arms are likely to be older than he thinks, The nickel plated Spyder arms with the oval section tubing are likely to be mid to late 80's. The set I got was NOS from Marc Evans in 1993 (memory again) and he had them for a while, the next set I ordered from Spyder in 93 or 94 and was manufactured from "flattened" round stock. I guess if you can detect the problem by the seat of your pants on the street you need to watch the license in your wallet more than the money that it contains. As Bill mentioned the rod ends only allow for .025 of distance change for either the 7/16 or 1/2 x 20 tpi. and not likely to get exactly the spec that you would like. The "turnbuckle" will give you what you want but it's not anything I would want to do with a rear arm. I just don't like the idea of cutting an arm, I guess they call that a personal preference.

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PostPost by: rgh0 » Mon Dec 31, 2012 3:13 pm

Quart Meg Miles wrote:Does anyone know, or can they measure, the elasticity of fitted newish rubber bushes, old ones that Gary has soaked in oil for forty years and modern poly?uro versions? Answers in lb/inch or kg/mm please or whatever.

My interest is the distortion they suffer from the torque of the wheel under hard acceleration and even harder braking, both of which will affect the toe-in/out. I once detected a failed rear wheel bearing, and knew which side, by the car's directional change under and off power.



I dont know the numbers but the poly bushes I have used would be more than 10 times stiffer than the inner A frame bushes which have a substantial rubber thickness. You can feel the toe change in a plus 2 due to movement in the rubber bushes from power on to power of.

Not as easy to feel in an Elan with its shorter A frames but the poly bushes does make braking more stable on the track as they limit toe change better under braking loads.

cheers
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PostPost by: worzel » Mon Dec 31, 2012 8:35 pm

Hi

Pictures of the TTR frames adjustable and retaining the rubber bushes.

Hope they explain what I was getting at.

Regards

John
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IMG_0374.JPG and
IMG_0373.JPG and
IMG_0372.JPG and
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PostPost by: Elanman99 » Mon Dec 31, 2012 9:06 pm

Are the TTR adjustable wishbones designed specifically for use with Polyurethane bushes?

I ask because my understanding of the Elan suspension is that the standard rubber bushes are fully bonded and suspension movement relies on the rubber 'stretching' as the inner and outer parts rotate relative to each other. After all that is the reason the suspension bolts are finally tightened with the car at loaded ride height.

It appears to me that the threaded portion of the wishbone will be continuously subject to bending forces and looks a candidate for early failure. I suppose for racing purposes the parts might be crack tested frequently but it seems a poor design, unless it was actually intended to Poly bushes. It not visible in the picture but the threaded part shown looks more like a bit of 'Allthread' rather than a purpose made high tensile fitting.


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PostPost by: worzel » Tue Jan 01, 2013 3:25 pm

Hi Ian

Fair point- originally both the TTR adjustables were only alterable off the car which although it would have worked was inconvenient. I had two new ones made from suitably graded steel by a local machinist I know and have used for years. TT assured me that the steel on his original threaded bits was of a suitable grade although the length of the thread exposed would seem to suggest that bending would not be a problem anyway as it's only about half inch or so.

Regards

John
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PostPost by: worzel » Tue Jan 01, 2013 3:27 pm

Hi- again.

One other point- the housings for the rubber bushes and the threaded section are made from one piece high tensile steel- not welded as per the originals- I thought this an extra safety measure.

Regards

John
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PostPost by: Elanman99 » Tue Jan 01, 2013 3:40 pm

John

Ah, so I understand that they are not as originally manufactured by TTR, but have been modified?

I agree the length of the thread is quite short, but the effective strength is limited by the root diameter of the thread. Also the details of how the threaded portion terminates to the end fitting needs to be considered to avoid stress concentration points.

If it were on my car I would hope that a thread used in that position was something heftier than 7/16" or 1/2".

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PostPost by: alexblack13 » Tue Jan 01, 2013 8:37 pm

Hi Guys,
When I stripped down my Sprint for its much required restoration. I removed the A frames and was able to bend them over my Knee!!!!! They were almost rusted through. :shock: Wahhwooow..... 10 months MOT too..... There were no stresses due to braking though. The discs and Calipers were U/S too.. :lol: :lol: :lol:

My pennies worth.. Don't try making your own adjustable A frames even if copying the Spyder or whoever items without the right skills and equipment...

Also. A good idea for a road car (I would not mod the A frames on a racer. Better to be 'store bought'). Might be to get the adjustable A frames set up as required and then take the measurements from them. Then 'correct' a new set from whoever or indeed have a set made to the dimensions you now know to give the correct toe.

I copied the professionally produced items with a bit of belt and braces. The adjustment required to give the right toe in was minute. Very happy with the set up so far but I don't thrash the car .... Eerr, eemm,,,, mutch! :roll:

I have Poly Bushes at the strut ends and inboard ends. Never noticed any difference in smoothness / harshness etc & the car runs like it's on rails.

Careful Guys... And a good healthy and happy new year. Lets hope it's a bit drier (in the UK) eh!!

Alex B..... 8)
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PostPost by: stevebroad » Tue Jan 01, 2013 9:51 pm

alexblack13 wrote:My pennies worth.. Don't try making your own adjustable A frames even if copying the Spyder or whoever items without the right skills and equipment...


Bugger! Now you tell me! :-)
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PostPost by: alexblack13 » Tue Jan 01, 2013 10:31 pm

Hardly aimed at you Steve. I suspect you will manage nicely. :wink:

ab
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PostPost by: ceejay » Tue Jan 01, 2013 11:55 pm

I agree, if you don't understand what you are doing, don't attempt
any kind of suspension fabricating, but if you do have the skills,
and or, you are willing to learn, then DIY fabrication is not beyond
the reach of the really serious elan owner.

Many of us are lucky to have had some kind of engineering
background, coupled with a lifetime of hard won experience,
projects such as this are not that difficult to complete.

Think about what you are doing, be dead accurate with all
measurements, use the right machines & tools for the job
so that everything fits together correctly in the jig, and
then carefully weld the parts together.

Photo below:
Rear shot of the chassis work in progress documented
on the 28-12-2011. And to think the elan is now nearly
ready for a test drive on the road after fours years of
hard yakka.
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rear-susp-06 .jpg and
self fabricated rear adjustable lower A arms - Adjustable spring platforms - Gusseted rear tray supports. Documented 28-12-2011.
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PostPost by: stevebroad » Wed Jan 02, 2013 12:31 am

That's an interesting mod to the tray supports. Why did you decide to do that? Are the original tubes a weak point?
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PostPost by: stevebroad » Wed Jan 02, 2013 12:31 am

alexblack13 wrote:Hardly aimed at you Steve. I suspect you will manage nicely. :wink:

ab


Thanks, I hope so :-)
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PostPost by: ceejay » Wed Jan 02, 2013 12:48 am

I saw the mod on a race elan chassis somewhere back in the 80s,
and decided to do same on the S2.... the rear tray support
tubes are known to flex... they don't after this mod.
Again a lot of work to do, but I enjoy fabricating.
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