speedjeans
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| posted on 9/12/15 at 12:40 AM |
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Lowering tvr / cortina suspension
Hi all,
I am MArco from the netherlands and all new here.
Also not really building a locost, but I guess with all these technical carbuilders this must be the place for me to stop by.
Basicly I built porsches 356, all low and custom, but now moving on to a new project: TVR WEDGE BASED 300SL..
As I want it low on the ground I was wondering if there are people here that are familiar with the TVR/cortina suspension.
1. What is the best way to lower the cortina front suspension (are there dropped spindles that will fit, anybody making custom wishbone and lower arms
for camber adjustments, etc) prob will go for airride.
2. On the tvr rear (half jag/half tvr) there is a trailing arm that rotates at a forward point. How can it make a make a circular motion (suspension
up/down) when the driveshaft/hub is mounted on an a-frame (wishbone).
And how will the camber of the wheel change when I lower the car (10-15cm lower). I was thinking that the hub will turn around the a-frame (getting
shorter on a horizontal plane, with the driveshaft ofcourse staying the same length, it will get a positive camber ? Are there custom a-frames
available?
see link, scroll down to last part:
http://www.wedgeneering.co.uk/TVR%20390SE%20p13.html
there are loads of other questions but these are the first ones I run into..
thanks for your time.
here some older builds:
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speedjeans
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| posted on 9/12/15 at 10:40 AM |
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this is what I mean..
thanks
[img]https://fbcdn-sphotos-e-a.akamaihd.net/hphotos-ak-xfa1/v/t1.0-9/11218610_10208099582546665_8560069701576477659_n.jpg?oh=c03f7f6a9928b2230597545d1
7fff72b&oe=56D3D41D&__gda__=1461596400_8ae97b2becefa05192f087dd74c41a8b[/img]
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Dick Axtell
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| posted on 9/12/15 at 11:37 AM |
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Tried to make the linlky -
https://fbcdn-sphotos-e-a.akamaihd.net/hphotos-ak-xfa1/v/t1.0-9/11218610_10208099582546665_8560069701576477659_n.jpg?oh=c03f7f6a9928b2230597545d1
7fff72b&oe=56D3D41D&__gda__=1461596400_8ae97b2becefa05192f087dd74c41a8b
Now I can see what you mean! The top mounting of the coil-over strut is fixed, whereas the lower end, which is fixed to the hub carrier, has to move
with a small degree of circular locus. This tends to reduce the wheelbase very slightly. Not 100% sure about the camber angle, but I suspect it
changes.
I'm interested to read what the LCB collective might comment.
2nd edit:
Have had another look at your 1st link, which carries some very interesting photos. I have seen that the A-frame and drive shaft form a double
wishbone arrangement, very similar to the old XJ6 rear suspension (which presumably supplies parts for this TVR). For camber change analysis,
you'll have to measure the suspension pick-up points, the articulation points on the drive shaft, and plot them out in front elevation. Then you
can move the hub carrier in "bump" mode, to check for change in camber angle.
[Edited on 9/12/15 by Dick Axtell]
[Edited on 9/12/15 by Dick Axtell]
Work-in-Progress: Changed to Zetec + T9. Still trying!!
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Sam_68
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| posted on 9/12/15 at 12:23 PM |
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Hi Marco,
To answer your questions:
1) 'Genuine' Cortina uprights are now getting rare and in any case, being cast iron, are not sensibly capable of being modified to meet
your requirements. There are several companies who make aluminium replacements to identical geometry, however, and some of these would be easy enough
to modify for a dropped spindle position. For example, we're working with Hi-Spec, who have been helpful in supplying modified uprights to our
requirements; this is an image of the CAD model for their 'Cortina' front upright, and you can see that it would be easy to raise the
spindle position:
2) As you have realised, there is a conflict in the arcs of the rear suspension components; the trailing arm tries to pull the outer end of the
wishbone forward as it moves through its arc (changing the toe), whilst the wishbone tries to move the upright end of the trailing arm in and out,
relative to the longitudinal centreline of the chassis. The geometry is not perfect, but the conflicting movement is quite small and will be absorbed
by the bushes. Dropping the suspension is likely to move the arcs into a more unfavourable part of their working range, but you'd need to do a
computer analysis, using 3D suspension analysis software (the free, basic 2D programs like VSusp aren't sophisticated enough) to figure out the
exact magnitude of the effect. If you can provide accurate measurements for the chassis/upright pickup positions, and grease palms with a small
quantity of silver, there are several specialists, myself included, who can do this analysis for you and recommend/design modified
geometry/components, if necessary.
I'm not aware of any off-the-shelf A-frames designed to work with lowered suspension on the TVR, but 'custom' A-frames, by their
very nature, would be manufactured to suit and there are any number of specialist fabricators who can manufacture what you want: it's not
complicated. 
edited to add:
If you're planning to 'slam' the suspension as low as the Porsches/VW you pictured, the geometry of the suspension as it moves
becomes pretty much academic, anyway, as you'll need to run it so stiff, to prevent grounding, that there will be hardly any geometric movement
to worry about.
[Edited on 9/12/15 by Sam_68]
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Neville Jones
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| posted on 9/12/15 at 05:48 PM |
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Modifying any cast upright is fraught with danger, steel or cast aluminum.
Fabricating steel uprights to suit isn't all that difficult.
Or you could get some Mustang 2 uprights from USA, which come in standard or lowered configuration, with the axle moved up. Very similar to Cortina
and the bigger Granada/Taunus.
[Edited on 9/12/15 by Neville Jones]
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Sam_68
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| posted on 9/12/15 at 06:19 PM |
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quote:
Originally posted by Neville Jones
Modifying any cast upright is fraught with danger, steel or cast aluminum.
You wouldn't need to modify the casting, and they will alter the machining to suit your required dimensions. As you can see from the drawing I
posted above, it's simply a matter of raising the position that it's drilled & countersunk for the spindle (stub axle).
Edited to to add image of the same upright:
The Mustang upright is quite different geometry, incidentally, so would require a comprehensive redesign of the suspension.
[Edited on 9/12/15 by Sam_68]
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Neville Jones
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| posted on 9/12/15 at 07:53 PM |
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The mustang spindle would be the obvious choice, with a shorter top wishbone.
Or a custom made fabricated item.
The ali uprights being referred to have a boss that is drilled. To move the axle drilling by 2" is asking for big problems.
Added to that, the car in the top pic has a thumping great V8 in it, and needs an upright of substance. The USA Mustang uprights can be had in ali and
steel, and the steel items are relatively cheap, and well up to the job in yank hotrods.
[Edited on 9/12/15 by Neville Jones]
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speedjeans
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| posted on 9/12/15 at 08:37 PM |
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Thanks.. more stuff to read in to :-)
i saw granada dropped spindles in the Us, but looking at the pics, they differ from the UK granada spindles.
have mailed fatman for more specifications..
http://www.fatmanfabrications.co/products/1975-1983-ford-grana
da-dropped-spindles/
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britishtrident
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| posted on 9/12/15 at 10:08 PM |
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What suspension. !
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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