65 replies to this topic

[76lxhatch]

Not trying to rain on your parade but the bump steer could change significantly if you still don't have shims set to the desired static alignment, you really need to do that first. Because it moves the upper arm (and indirectly the steering arm) around it changes the position/arc of the wheel (which the tie rod needs to match for minimal bump steer).

Its an extreme example but I did some measurements comparing maximum positive caster settings to maximum negative caster settings and found up to 20mm difference in bump steer, in excess of 3mm immediately off ride height.

[76lxhatch]

In that case it sounds like you also want to determine (roughly) what the actual ride height will be so you can figure out the total travel - could be as little as 40mm in compression which would affect the camber gain options.

Didn't realise that the extended ball joint would bind to the point of not even reaching the bump stops. Very interested to see how it all comes out especially with the upper arm canted for anti-dive.

[76lxhatch]

That's the basic version of the caster calculation, which is probably near enough. If you're interested here is an example of the wheel alignment sheet I use with a slightly more accurate calculation:



You can usually work on the chassis rails and cross member being level, all depends on how you set the car up with springs of course. As long as the caster is even side to side you probably just want to get the maximum you can since its unlikely to be excessive (note GMH max shim stack 0.5" if legality is a concern), with static camber in the ball park at ride height.

I have wondered about the app thing but came to the conclusion that a phone probably isn't particularly accurate with its angle measurements especially since many don't have properly flat edges.

[Bigfella237]

Love yer work Tony! Just to clarify your UCA mounting position, I assume your holes are 16mm & 32mm lower than the standard UC mounting holes, but are all UC mounting holes in the same place?

 

And say somebody has an LH k-member, is there some other common point from which you could measure that will be the same on any Torana? Or would they have to set everything up as you have and take their own measurements?

 

One last thing, I note you have Nolathane bushes in the steering rack mounts, if someone were planning on replacing these with solid alloy bushes, would offsetting the rack up or down slightly help with tuning the bump steer (not that you need to)?

[axistr]

The only way you can get zero toe movement through out the suspension travel is to have the inner steering rack ball socket centre at exactly the same height and centreline as the lower inner control arm mount pivot bolts, and the outer tie rod end ball centre must be inline and same height as the lower control arm ball joint centre. You can also have these rack ball joint centres above the lower control arm mount pivot and lower ball joint but must be at the same centreline heights.(ie standard holden design) The problem with the raised heights is you must have even length top and bottom control arms to achieve zero toe bump steer and that isn't going to happen with the torana setup.

 

The stub axle close to inline height with the lower ball joint is also desirable to keep things better inline. As previously mentioned  bump steer or the movement in an unwanted direction is just as common from excessive movement in camber and or caster.   

[76lxhatch]

By my calculation 0.07 degrees over a 600mm diameter wheel/tyre is ~1.5mm (got to account for both sides) change in toe, which is very good. I only got mine down to about 2.5mm.

Yes moving the rack does help with bump steer (and is one of the main reasons you would move it). If that and the Ackermann geometry comes out correct (as well as ensuring its on centre) you can generally be assured it will be fine. If you are moving outer ends by much you will usually find you need to move the inner ends to match.

[Rockoz]

Just wondering if the picture that is on here with the chassis measurements will help you determine the angle of the crossmember.

Someone will know where to find it for you.

[axistr]

Tony I reckon your better off with the least amount of caster change throughout the suspension travel as possible, hitting a decent bump at speed and finding out you have just added two degrees more caster on one side will very quickly steer you in an unwanted direction. Going on some of the graphs you have posted the car could move across the road substantially before you could properly correct it.  I would prefer a small amount of toe change over any caster variation between sides.

 

I also found an old picture I took of a Torana on my alignment machine some time ago, This thing was a real mess when it turned up and I had to change steering arms and correct bent parts and start from scratch. It had major bump steer problems which we had to iron out.  I scribbled on the photo which helps explain the importance of even rack tie rod bar to cross member and lower ball joint heights. And the importance of having level tie rod bars at ride height. 

 

 

   

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[Bart]

I like those top ball joints. I have similar in my LJ where tapered pin can be removed and swapped for a longer or shorter pin.
My top ball joints are also Chrysler screw in ball joints.

Edited by Bart, 11 December 2016 - 03:34 PM.

[mattie304]

What stubs and steering arms are you running ?

[71XY]

Right so he made it to Summernats after a couple of all nighters getting the front end back together... https://m.facebook.c...801630306777740 And despite limited miles he told me is was pretty good to steer so that was a win. Sadly it managed to have an engine bay fire fuelled by trans fluid a couple I've outings later and has been off the road since. While the blower out the bonnet was always a cool look, it had that wow factor which really attracts police attention and a defect to go with it. So now they're trying to fit a late model factory supercharged Corvette engine... and it's just too big to fit under the bonnet. The *GENIUS* solution was to section the middle out of the crossmember and lower it about 100mm(?) and take the steering rack with it. They know not what they've done.

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[71XY]

I can't unsee it...

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[71XY]

I haven't looked to see how they gor a steering shaft to it; through the crossmember.

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[71XY]

I guess my only question is what can they do with it? I'm probably not going to be into it this time. I was heavily invested in the last attempt and not really consulted on what's happened since. Same token I don't want to see him in an undriveable hunk of shit. I heard they were struggling to fit the new donk & was initially pleased they didn't just bin the front end and put a tube steel one in... but in retrospect this is worse for all concerned. Can it be saved with some unconventional steering arms (orange) and a bump steer kit like they make for a Mustang (blue) with rose joints (yellow) Or do we make it much easier (or actually possible) to install an exhaust by resorting to an aftermarket front end like MacDonald Bros? Do those things even steer or are they just for drag racers? ¯\_(ツ)_/¯

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