hillbillyracer
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| posted on 16/12/09 at 08:26 PM |
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De-dion width & trailing arm length.
Having given some thought & done a bit of research (some on here!) I've decided to convert the live axle in my project to a De-dion.
The car is the Autotune Gemini that Trev Borg had.
The reasons are I have all the doner bits from a Sierra & am leaning toward building the car with them to get an age related plate which I'd
prefer & with regard to the rear suspension I'm looking for better ride, handling, parts availability, strength & the availability of an
LSD.
I'll be building my own axle & have looked about for plans but I'm pondering what to do width the width, stay with the Escort width or
go to the Sierra to get more stability (as if it it's gonna have a high COG!) & run the stock shafts but run into possible bodywork mods to
deal with the width of modify the shafts to use the Escort track width?
Here a few pics to show how the wheel sits in the arch, it shows a fair bit of tyre tread as it is:
These tyres are 185/60/13 & I may well change to 195/50/15 as I need to clear the Sierra brakes & searching on here suggests they're
popular.
I plan to use the same size & wheel offset all round & that will be what works well with the front suspension.
I've had a quick search aboot the tinerweb & not found an real specs for track width or hub to hub measurements for the Sierra & Escort,
loads about total width, length etc but not what I'm looking for.
When i'm on sorting the rear suspension opinion has it longer links are better & that most sevens have them a bit short, as they are on this
car. What gains am I going to see by making them longer & by how much? The advantage I have is with the full bodywork I have room to do something
about it as these couple of pics show:
Extra axle width would help making more room for links between the wheel & chassis:
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hillbillyracer
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| posted on 16/12/09 at 10:29 PM |
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Well I thought I might get at least a reply telling me not to waste my time with a De-dion & I should be going to do double wishbone IRS &
another telling me the live axle was as good as anything else & not to bother!
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djtom
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| posted on 16/12/09 at 10:32 PM |
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I've spent the last couple of months doing the same to my Tiger - changed from a Cortina live axle to a de-dion setup. Not overly difficult, but
I have complicated things for myself by lengthening the trailing arms to reduce the roll steer and adding a rear anti-roll bar (still in the
construction phase at the moment!).
It's not back on the road yet so I can't give feedback on how well it works, but it should reduce unsprung weight, reduce roll steer and
most importantly for me, allow me to have an LSD, as there were none available for the Cortina axle.
Let us know how you get on.
Tom
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hillbillyracer
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| posted on 16/12/09 at 11:27 PM |
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Thanks for the reply, which plans are you using or have you just made a jig from the Cortina axle & make the De-dion the same width?
I'm still at the planning stage & the rest of the car is still to do too, this is one of those cars that's been through a few owners
but never been finished. I intend to finish it but it'll be doing well to be IVA'd before the end of next year.
This is the first bit I want to tackle, something I can get my teeth into & make real progress to help kick the build along I'm thinking.
The only thing stopping me going for the full width Sierra size is the bodywork, it's showing a fair bit of tread as it is without adding a
couple of inches to the axle width & going up a tyre size too. I suppose I'm looking for opinions on how the arch sits over the wheel, I
cant just buy wider arches for this! Adding some extra width to the arches is not out of the question though as I'm thinking this will be to
paint rather than use the gelcoat finish because the level between seams from the moulding is too far out, as much as 2mm in places so it will need
filling & painting anyway.
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HOL
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| posted on 17/12/09 at 10:54 AM |
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Tom thread is a good souirce of info.
http://www.locostbuilders.co.uk/viewthread.php?tid=101532
he is using a standard GTS de dion, which if you look at their (GTS' site, they can also be made for the standard book chassis.
Dependent on space for the new diff and the original tank, your problems could simply be restricted to the need for wider arches.
Andy
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Willie
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| posted on 17/12/09 at 10:51 PM |
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So your main reason for doing this is to get an age related plate? If that's the case, what all do you need to use from the Sierra to
qualify?
A decent live axle setup is hard to beat. On the road a good De Dion will be better, but if you get it wrong, it could be a complete dog.
Generally speaking, the longer any suspension link is, the better, as it draws a bigger arc when pivoting, therefore the fore/aft movement is less
over a given amount of vertical. If you're with me on that.
Caterhams have 2 trailing arms and a A-Frame locating the de dion, with shorter than standard Sierra driveshafts. Why not run shorter driveshafts to
suit your track?
My main worry would be the chassis pickup point for the diff. If it hasn't been designed for it, you're going to be in trouble. You need
really good bracing around the diff, so that when you drop the clutch it doesn't turn the bulkhead upside down. Early Caterham chassis'
had a habit of ripping diff mounts out, so this is something to consider.
If you do decide to go for it, I suggest you consider roll-centres. You want your rear roll centre to be slightly higher than the front, so
you'll need to work out where your front roll centre is. From this you can determine the rear and then design your near rear suspension to suit
it. You'll almost certainly still get it wrong, so build in plenty of adjustment. Any modifications I've done to suspension I've
tried to include rose joints or plenty of mounting positions, so I can adjust it and see if it gets better/worse in a particular direction.
I'm all for big projects, and I'm all on for making your own stuff, so if you really fancy doing it, go for it. Just realise that its not
a case of knocking it up and nailing it on...it will take a fair bit of head scratching to get something that works properly.
Just my 2p. All the best with the project.
Willie
Willie
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hillbillyracer
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| posted on 18/12/09 at 08:24 AM |
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Cheers for the replies, the age related plate is just part or it, it's the stronger diff, better availability of an LSD & different ratios
& better ride & handling (if as you say I dont cock it up!).
On top of all that I want to do the job, I like making stuff! 
Mabye I should point out I'm an Agric Engnineer & have did my City & guilds in Fabrication & Welding on leaving school in the early
90s. Working out the areas that need bracing to take the torque reaction through the diff & the new mounts for the trailing arms is no problem,
but the effect on handling, the roll centre are going to take more thought.
Cheers for the link to djtom's thread, I'd been thinking of making my own axle using a jig along the same principle as the one he's
used to modify the GTS axle.
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