Coilovers

[99176]

If someone had finally finished making up his top links and now wants to dispense with the transverse spring.
How would he go about selecting shocker sizes and spring rates and lengths ?
Let's assume he has a MkII GT6  :) :)

[piman]

Hello 99176,

if you can't find anyone that has done it and copy his settings, then I think you will have to start with the spring rate of the original spring and the wheel travel and work from there. The advantage of coil over springs is a large range of available springs and their relatively cheap price so you can experiment somewhat?

Alec

[99176]

Well, after poking about with a tape measure and scanning the 'net.
I think it will be something on the lines of 8.5'' - 12'' AVO's with 6'', 200lb springs.
Someone here must have already done this and can steer me through the endless combinations.

[GT6 M]

If you aint got the geometry reet, then there be even more camber change than original set up
and also the top wish bone has got to be very stiff,to stop twist.
the rear spring actually helps alott in camber reduction,and also location.

If ye going some where along this line, it may be better.
as its still got top spring location!!!



or this set up,  this is an early set up, latest uses a whisbone from diff to link adjustment.
prob is,the bushes are not solid inside,and also alot of links/ joints to make move ment.



M

[99176]

Marcus,
  Hi. I already have tubular bottom wishbones and have now made top arms pivotted from a billet aluminium crossmember mounted on the diff.
This gives me near equal lengths top and bottom. One polibush at end of crossmember and one rose joint to upright per side
I really need guidance with length of shocks and, more importantly, length of spring.

[piman]

Hello 99176,

The damper length is based on the total wheel travel you want and the location of your mounting points. The spring length then is related to the damper length. I would suggest talking to the damper and spring manufacturers technical department for advice and technical data?

Alec

[GT6 M]

quite easy really, you aint got much doon wards travel,
as the drive shaft hits the chassis.
So measure the down ward movement,and then the top,{ where you think it will go to }
and you got what you after.
looking at the first pic,you can get a good idea,  You really need adjustables too.

I would have thought about 170 ish lbs would have been OK
but all depends on how stiff you want it to be.
the more upreet the spring,the less poundage that ye need.
as a guide the GT frunts are 200ish as standard, BUT,the springs are inclined so much,that they loose effect.
As  Alec says, speak to spring manufacturers, give em the weight of car at rear. and they will have charts to say wats wat.

one thing that seems to quirk me mind is twist, due to having the coilowa on one side only, maybe just me, but would think two be better to even it up
like what the Jag rear end has

got any picks to put up.  we all like pics on here. ;)
as im sure a few others be intrested,
I am, as any thing tinkered  wid is of intrest to me. :)
ohh here is the other pic that did,nt come up.



M

[thescrapman]

Having a spring on just one side of the rear upright will give rear wheel steer even if everything seems very solid.

Even with rose joints and a sturdy top link the back end will still fidget under you with a single offset spring.

Lewis Jones has been trying to sort his Supercharged Spitfire for a while now.

Cheers

Colin

[TimW]

99176 wrote:

Well, after poking about with a tape measure and scanning the 'net.
I think it will be something on the lines of 8.5'' - 12'' AVO's with 6'', 200lb springs.
Someone here must have already done this and can steer me through the endless combinations.

Keith I have dumped my AVO's for GAZ and find them far superior.  The dampening rates on the GAZ I find much more suitable to the GT6.  GAZ will make you a pair of height adjustable units to suit if you give them the open and closed dimensions and they are very reasonably priced which helps!!!!!  If you use AVO's be prepared to change the bushes every 1000miles!!!!!  GAZ use full width bushes.

[GT6 M]

339 wrote:

Keith I have dumped my AVO's for GAZ and find them far superior.  The dampening rates on the GAZ I find much more suitable to the GT6.  GAZ will make you a pair of height adjustable units to suit if you give them the open and closed dimensions and they are very reasonably priced which helps!!!!!  If you use AVO's be prepared to change the bushes every 1000miles!!!!!  GAZ use full width bushes.

True, I find both the spax,and the avo,s too hard for the rear.
BUT, AVO will, at no extra cost if they are got from them alter the valving,so settings become softer at the bottom, but loose oot at the top
I donrt think any yan has used either on a GT / Spitty, over 4, as it gets rock ard

used ones can be altered too, but was told it would be 12£ +vat + postage
basicly a rebuilt damper,or refurbished.
the bush question is easily resolved, the same bush thats used in the spring eyes,the inner pivots at rear will fit.
outer steel case,and inner steel bush.

Cols on my line o tinking with the one sided coil owas.
maybe some thing to consider ,!!!
any thing with a rear radius arm thats short, will give rear steer.
so maybe some thing else t consider.

M

M

[TimW]

796 wrote:

True, I find both the spax,and the avo,s too hard for the rear.
BUT, AVO will, at no extra cost if they are got from them alter the valving,so settings become softer at the bottom, but loose oot at the top
I donrt think any yan has used either on a GT / Spitty, over 4, as it gets rock ard

used ones can be altered too, but was told it would be 12£ +vat + postage
basicly a rebuilt damper,or refurbished.
the bush question is easily resolved, the same bush thats used in the spring eyes,the inner pivots at rear will fit.
outer steel case,and inner steel bush.

Cols on my line o tinking with the one sided coil owas.
maybe some thing to consider ,!!!
any thing with a rear radius arm thats short, will give rear steer.
so maybe some thing else t consider.

M

M

I know you have found a good solution for the bush problem but if buying new in the first place then i would spend my money with GAZ every day of the week :) :)

[GT6 M]

come on Keith, get some pics up.



;) M

[GT6 M]

this is the latest version of the  modded back end.
just incase any yan intrested.


M

[piman]

Hello,

The weak point is the single inner pivot on the bottom arm, it needs to be modified so that there are two, probably easier to fabricate a new arm, and if strong enough there will be very little twist due to the offset spring location.

Alec

[Davemate]

thescrapman wrote:

Having a spring on just one side of the rear upright will give rear wheel steer even if everything seems solid
Lewis Jones has been trying to sort his Supercharged Spitfire for a while now.
Cheers
Colin

Mr jones has put the transverse spring back on !
" the rear end was twitchy" he said. " less so when the bushes are new but they only last a thousand or so miles" but he did add " there are two shocks on a jag rear end to stop the twitchyness"

[piman]

Hello Dave,

the Jaguar independent  uses twin spring damper units because the upper link, which is the drive shaft articulates and so has no fore and aft restraint.
While that approach would probably work, it is more expensive than making a better lower arm especially as in the case quoted the spring damper has already been bought. Ideally a wishbone upper arm would be an advantage and a lighter lower arm could then be used.

Alec

[JohnD]

Marcus,
This is constructive criticism, in a cooperative spirit, 'coz I admire your mods!

First, that great heavy wishbone!  Less strain on the coilover setup if you replace with a skeleton tubular one, apart from any 'unsprung weight' issues.

Second, the adaptor bracket for the diff.     A single flat(ish) plate, that would allow significant flexing, so that the front of the diff can move up and down in response to torque.  No suspension effect, but bad for the propshaft and the internal bearings?   You have through bolts in the diff.nose casting - how about a second plate from the top of the nose casting going out to the chassis mounts to triangulate the bracket and make it rigid?

John

[Nick Jones]

Think those are pics of the KD Triumph one John.

My own opinion is that there isn't too much wrong with the transverse leaf. Leaf springs are rising rate and self damping (to an extent) and will also do a better job of locating the upper end of the vertical link than anything short of a true upper wishbone.

Nick

[piman]

Hello Nick,

very true but the disadvantage is the restriction on rate compared to the relatively cheap and varied coil sizes available.

Alec

[GT6 M]

Just a thought Keith, are you aware the upright is angled doon wards about 3 degs, this to give castor
So you need to really keep this angle.

M

[Nick Jones]

piman wrote:

Hello Nick,

very true but the disadvantage is the restriction on rate compared to the relatively cheap and varied coil sizes available.

Alec

Sure, but as you are mostly wanting to increase the rate, retain the leaf spring and add coil-overs to assist.  Also, I've had some success in the past adding leaves (some upside down) to increase the rate.

IMO, doing away with the spring altogether just leads to location issues.

Nick

[piman]

Hello Marcus,

castor is not required on the rear wheels?

Alec

[Deleted User]

796 wrote:

this is the latest version of the  modded back end.
just incase any yan intrested.


M

M whose back end is that? yours?

Rob

[smithy]

You don't recognise M's back end Rob? That must be someone else's. His un's red - Babboon style.  ;)

[99176]

Both of Marcus' pics are MkI and MkII 'work in progress' by my son.
I am approaching this from a slightly different angle.
All geometry will be as original, but I am aware of the problems associated with offset springing.
BTW I do like AVO,s but admit to fitting spherical bearings every time.