AdamR
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| posted on 15/5/07 at 11:47 PM |
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de-dion shock mounts
I got some nice shiny Protechs from MNR recently and set about positioning the mounts at the weekend.
However the ride height is way too high using the brackets on my GTS de-dion axle. Not sure how GTS builders have gotten around this as my shocks are
only one inch longer than GTS spec at 13" fully open.
 
rear shock position 1
Currently full droop is reached when the trailing arms contact the chassis rather than the shock fully extending, which is obviously no good.
So what I propose doing is lopping off the existing mounts on the de-dion and adding some new ones slightly further inboard and on the beam itself.
This adds an angle to the shock. Anyone see a problem with this?
 
rear shock position 2
This should give me a decent ride height whist being able to use all of the shock travel - important when there's only 3" of it!
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Mr G
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| posted on 16/5/07 at 01:15 AM |
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Early Mk/Ron champion de-dion allowed longer upper trailing arm bolt to permit mounting of the damper in single shear.
This is of course dependant on the location of your damper top mounts as well.
 
de dion
Normal is getting dressed in clothes that you buy for work and driving through traffic in a
car that you are still paying for - in order to get to the job you need to pay for the clothes
and the car, and the house you leave vacant all day so you can afford to live in it.
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flak monkey
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| posted on 16/5/07 at 07:01 AM |
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You have 3 options from the way I see it:
1. Get some shorter springs for your shocks. This will allow you to lower the ride height.
2. Get the correct length shocks (12"
3. Modify the axle.
Personally I would go for #1.
 
David
Sera
http://www.motosera.com
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Ivan
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| posted on 16/5/07 at 07:28 AM |
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If there's space with the wheel why not add a bracket just outside the trailing arm bracket and use a common bolt to mount shock and trailing
arm.
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AdamR
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| posted on 16/5/07 at 08:28 AM |
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Thanks for the suggestions so far. 
Mounting on the same bolt as the upper trailing arm is a reasonable suggestion, but I don't know if it buys me enough extra space. Unless,
I'm getting something wrong in my thinking, which is a definite possibility.
Flak monkey, your photo is interesting (not least because it answers another question I had about the panhard rod).... That looks to be about the
amount of droop I would have if I had 12" shocks, but I think the trailing arms need to be much more horizontal, even on full droop) to get a
reasonable ride height at the back. My target for reasonable ride height is 100mm front, 125mm rear. How much do you have? Am I missing something?
Also, I only have 3" of shock travel so I need to be able to use it all. That rules out shorter springs, or using too much spring preload for
that matter.
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flak monkey
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| posted on 16/5/07 at 08:33 AM |
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Mine is set to 125mm rear and 100mm front at the moment. This sees the trailing arms pointing very slightly down toward the back.
Those shocks are 12" as supplied by GTS.
Sera
http://www.motosera.com
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ned
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| posted on 16/5/07 at 08:50 AM |
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Adam,
After buying a couple of second hand shocks that were the wrong size I assembled the rear end and measured, then ordered shocks to suit, iirc mine are
at least an inch or two shorter than yours. I looked at swapping for shorter springs but there's not enough travel due to the shock body length,
I also looked at moving the pickup on the axle aswell but with the brake caliper in position the options seemed limited. Changing the shocks for ones
that actually fit is the best route imho as I've been there and done it. Protech may exchange your current shocks, even if you have to sell them
on here or ebay you will loose little or no money.
Ned.
beware, I've got yellow skin
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AdamR
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| posted on 16/5/07 at 09:06 AM |
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quote:
Originally posted by flak monkey
Mine is set to 125mm rear and 100mm front at the moment. This sees the trailing arms pointing very slightly down toward the back.
Those shocks are 12" as supplied by GTS.
Ok, looks like I'm aiming for the right sort of ride height at least.
From the look of your picture, if the trailing arms are almost horizontal at normal ride height then you must have very little shock travel left for
bump?
I'm aiming for 1" of available droop travel and 2" for bump. This seems to equate to shocks that are about 9.5" fully open
using the existing mounts!
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flak monkey
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| posted on 16/5/07 at 09:12 AM |
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They arent at as much of an angle as they look in that picture.
Once the car is down on the ground the trailing arms sit like this:
 
(Best pic i have, sorry)
Theres still a good amount of shock travel available, though How much I couldnt tell you for certain. Maybe 2".
There is no preload on the springs (175lb) to give 5" ride height.
David
Sera
http://www.motosera.com
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big_wasa
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| posted on 16/5/07 at 03:15 PM |
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Gts rear bulk-head is 1" taller than book.
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flak monkey
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| posted on 16/5/07 at 03:55 PM |
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quote:
Originally posted by big_wasa
Gts rear bulk-head is 1" taller than book.
Bloody good point, forgot that...
Sera
http://www.motosera.com
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AdamR
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| posted on 16/5/07 at 03:56 PM |
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quote:
Originally posted by big_wasa
Gts rear bulk-head is 1" taller than book.
Aha. Cheers for that. It's all starting to add up now.
Think I'll move the mounts as per my photo. Ned, your point about switching the shocks for some shorter ones is valid, but I reckon I can weld
on new mounts pretty easily that will align better with my upper mounts.
How does the added angle effect spring rate?
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MikeRJ
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| posted on 16/5/07 at 04:10 PM |
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Angling the shock reduces effective spring rate and damping action.
I have this problem with my chassis and a GTS axle, one possibility is to mount the damper on the inside of the top trailing arm bolt, either in
single shear (not technicaly good, but M12 bolt is up to the job IMO) or adding some bracketry to put the bolt in double shear.
You also lose the benefit of having the shock mounting eyes the "proper" way for the axle (i.e. like the GTS design), but lots of locosts
have live axles with the shocks mounted the other (book) way so it shouldn't cause problems.
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AdamR
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| posted on 16/5/07 at 05:29 PM |
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quote:
Originally posted by MikeRJ
Angling the shock reduces effective spring rate and damping action.
I have this problem with my chassis and a GTS axle, one possibility is to mount the damper on the inside of the top trailing arm bolt, either in
single shear (not technicaly good, but M12 bolt is up to the job IMO) or adding some bracketry to put the bolt in double shear.
You also lose the benefit of having the shock mounting eyes the "proper" way for the axle (i.e. like the GTS design), but lots of locosts
have live axles with the shocks mounted the other (book) way so it shouldn't cause problems.
OK. I think the 175lb springs may be over doing it at the rear, so I'm not worried if the effective spring rate is reduced a little.
On the issue of which way around to mount the shock, I think it's actually better to do it the book way. The trailing arms are much shorter than
the axle so there is benefit in allowing the shock to pivot on it's eyes in that plane. ...Not the best description, but makes sense to me.
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