VinceGledhill
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| posted on 4/9/03 at 11:32 AM |
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Wishbone Questions, Vince is in a Quandry.
I have read the other threads on here about wishbones and am considering a few matters and wondered if you guys could help.
1. I know that I need to make the top wishbone a few mm (not sure how many) further back at the top to get a bit more castor angle for self
correction.
Could I manage this with Sierra hubs and the offset top hat that MK make that goes into the top of the hub in place of the McPherson strut. Would
this be enough? Anyone done it?
Secondly, I am really concerned about bump steer. The only drawings that I posess are the ones in the book. I don't have anyone else's
drawings.
If I was to make my own wish bones then I would have to do them at book dimensions. I could then fiddle around with an escort steering rack to
eliminate the bump steer.
2. If I didn't make them myself as above, then I may look at purchasing MK ones. The reason for this is two fold.
1. it would save me lots of time,
2 I could get the slightly longer ones and therefore have a slightly wider track at the front which I think would look better with the capri live axle
that I plan on using at the back.
However, I have spoken with Martin at MK and he tells me that he will sell me parts, but won't give me measurements. With that in mind, I am
worried about bump steer.
3. Does the MK indi modified steering rack fit into a "similar" position on the MK chassis as it does on the locost chassis?
4. If I do decide to make my own wishbones, having a tig welder, I may make them from stainless and polish them up... anyone done this? Strength?
Regards
Vince Gledhill
Time Served Auto Electrician
Lucas Leeds 1979-1983
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JoelP
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| posted on 4/9/03 at 12:29 PM |
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Easy Vince, how are you?
I bought some top bones of him recently, i'll measure them and post it when i get up to the garage. His ones have an ofset built in for the
castor angle, but you can still change it by moving the brackets. Not sure that the top hats would give enough alone...
Bump steer, sod it... i'll eliminate mine when its running! You know about positioning the joint in the right place? I'd just aim for
that and fiddle later.
I think the castor angle is created by about 15mm ish at the top wishbone, BUT DONT QUOTE ME ON THAT!
Not a clue about stainless though!
Good luck
Joel
PS as for making you bones, id just work out the track you want and make them to fit. The bump steer stuff correlates to the gap at the front between
the brackets on either side mainly, as the wish bones get longer the track control arm just gets longer too. So provided you have a standard width
chassis, a standard width reduced rack should be a good start!
[Edited on 4/9/03 by JoelP]
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James
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| posted on 4/9/03 at 01:38 PM |
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Vince,
The Sierra track is 6/7" wider than the Escort at the front so even with the Cortina axle you'll end up with your front track being wider
than you rear.
Others can tell you their opinions on this- I've no idea what it'll mean handling wise.
You could perhaps compensate by getting rear wheels with a greater off-set or fitting spacers or something.
As regards castor:
The recommended 5.3(?)° equates to 22mm I believe (if I correctly recall Mark Allanson's calculations).
Whatever your wishbone gives you the MK insert allows you to modify this by +/-6.5mm. But! If you rely in this then you won't be able to use it
to modify your Camber at all (although this can be done by winding in/out your top balljoint).
If you do buy MK's front wishbones then you'll need to move rails FU1/2 (and I suspect 'E' aswell. Because they are wider.
You'll also have to move your steering rack mount backwards (as the centre line of the wishbones will move back with them being wider).
I'd recommend you make the wishbones to the 22mm and then use the inserts to 'fine-tune' the castor.
HTH,
James
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timf
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| posted on 4/9/03 at 02:19 PM |
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vince
also were you aware of the small cock-up in the book regarding trailing arm location
see http://forum.locostbuilders.co.uk/xmb/viewthread.php?tid=5170 for details
Tim
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stephen_gusterson
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| posted on 4/9/03 at 02:31 PM |
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http://www.1728.com/pythgorn.htm
The above link is a really interesting and useful aid in calc the sides of a triangle and angles.
You can input the vert distance from top and bottom joints, and the other side as the horiz and it will tell you the angles involved.
Also useful for rougth setting of toe in and camber.
bump steer is more a function of the position of the rack ball joint pivot points to the mounting points of the suspension than the absolute track
width.
its been said that they need to be on the same diagonal viewed from the front that passes between top and bottom pivot bolts. There is a lot of folk
lore and suck it and see on this subject tho.
The aussie rules allow 2mm max over travel!
In reality you may get a bit more than that.
On my car I got acceptable amounts by mounting the rack really far forward - without mods. I run same track as the donor car, but my wishbones are
longer than book - about 420mm or so.
I recon you will get best results by building the car with the correct track, and then getting your rack modified.
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VinceGledhill
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| posted on 4/9/03 at 04:20 PM |
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Thanks for your input guys. So don't really want a track at the front bigger than the back. It would look stupid. So I'll make my own
out of stainless (unless someone tells me not to because of safety etc.
If I adjust my Jig (per book Jig drawing) so that the top ball joint is say 5mm further back (please correct me with a better figure if you know of
one) will this not foul the coil over shock? Or will I have to use curved tube in order to not foul it in this instance?
Regards
Vince Gledhill
Time Served Auto Electrician
Lucas Leeds 1979-1983
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type 907
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| posted on 4/9/03 at 05:23 PM |
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Hi Vince
Wheeled out my stainless chassis the other day. If you need any info please feel free to U2U or email me. My photo archive shows wishbones &
rack ext. Had to drop the rack down 30mm from book (bump steer cure I hope). Posted a pic the other day you may have seen. Hope I can be of help
Paul
Too much is just enough
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Hugh Paterson
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| posted on 5/9/03 at 07:19 AM |
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Stainless chassis?
Paul very interesting stuff, what stainless did u use for the chassis tube or box section, 316 or somthing else?
Shug.
[Edited on 5/9/03 by Hugh Paterson]
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type 907
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| posted on 5/9/03 at 08:38 PM |
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Hi Hugh,
Yes, some of it is 316L, the rest is 304L, odd bit of titanium here & there.
Glad you find it of interest, most shy away from stainless. I just hate painting!!!!
Paul
Too much is just enough
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dblissett
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| posted on 1/10/03 at 06:20 PM |
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i was thinking of making the top two brackets on my front wishbones 45mm instead of the normal 40mm and then use spacers each side of the bushes to
gain caster adjustments
has anyone tried this
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Viper
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| posted on 1/10/03 at 06:26 PM |
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Vince, Dave
if you have a look in my archive you will see how i have made my top wishbones adjustable for castor, although iy is using a cortina upright i see no
reason why it won't work on a sierra upright.
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Dunc
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| posted on 3/10/03 at 02:11 PM |
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Heres something I threw together a couple of years back to help me out. It gives a static 2D view of roll angles/ centres etc. I'm not sure if I
ever completed all the other stuff as I went 3D to include things like castor change during and roll and effects of the steering rack on bump steer
etc. Hope it helps someone but it's just a guide, I think all the sums are right.
Dunc
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Dunc
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| posted on 3/10/03 at 08:26 PM |
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With the sierra upright you have to lean it back to get the right castor angle. This mean that the protrusion for the steering arm it pointing up and
not horizontal as it is in the sierra. This is because the other ball joint is at the top of the suspension strut on the sierra and gives the sierra
the correct castor unlike the cortina upright which had the ball joint above upright. Just in case you try and use 'book' wishbones and
end up with 5° of wrong castor angle.
You'd have thought Ford would of had the foresight to make sierra parts that could be used for Rons book back in the early 80's.
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TeamFalcon
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| posted on 8/10/03 at 05:11 PM |
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Bump steer
Vince,
I did'nt know what bump steer was when i read your post. Looked it up on the net and found the following link - which has a diagram at the
bottom. Don't know if it will be useful to you but was useful to me to understand what bump steer was.
http://www.longacreracing.com/articles/art.asp?ARTID=13
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Dale
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| posted on 10/10/03 at 05:01 PM |
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Dunc, that is a nice spreadsheet-although I dont understand most of it. But it has helped me out an increadible amount. I was wondering how much
camber and roll people have on finished cars. My design is wider track and narrower chassis at the front and I would like to try and maintain the
simmilar specs. So in a siimple way
amount of static camber
amount of camber at either suspension limit -as in full roll
how many degrees roll permitted before stops
and roll centers
Thanks
Dale
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Dunc
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| posted on 11/10/03 at 10:59 AM |
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Basically the spreadsheet was developed over a period of time and I just added to it. It could be much more user friendly and compact. You just need
to enter the centres of the ball joints and wishbone mounts from the car centre line, their height from the ground and the track from the centre of
the tyre.
You can then alter the amount of roll and see the change on the graph and read the change in camber for each wheel. Additionally you can enter the
position of the upper damper mount and it's % position along the lower wishbone and it'll calculate the change in length for a given roll
angle. Could help determine spring and damper sizes.
There's other stuff there too but thats the basics and should give you a guide.
Dunc
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