Right, should probably get the kit car finished now.

I'm slightly concerned that after fixing emissions my car is still going to fail on self centering so could anyone like to comment on the following solutions ripped from the dax forum?

low rear/high front tyre pressures (18r/35f psi)

positive caster angle - is this fixed by the wishbones? I'm having some difficultly understanding what angle this refers to on the front wheels.

toe-in/camber - anything that could help here?

loosing off bottom balljoint with a drift? - what exactly should I be doing with the drift? Just smacking the captive bolt around until it gets looser?

Anything else you can think of?

Thanks everyone.

Have you actually tried it? Drive it on full lock and see if the steering wheel tries to straighten up? That's all it needs to do, got to be worth a try before you start doing lots of extra stuff.

Hi, yes mate. It's one of the fail point on my initial IVA test sheet.

The tester said he wanted to be able to drive the car in a big S at 30mph and it show some indication of straightening up coming out of each bend no handed.

Caster is the angle between the top and bottom ball joints viewed from the side, and the vertical line from one of them to the ground. Can only be increased by moving the top wishbone back (or the bottom one forward)

quote:

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Originally posted by interestedparty
Can only be increased by moving the top wishbone back (or the bottom one forward)

---

I'm fine with temporary fixes.

Will a spring stay behind the track rod ends during driving?

With respect, don't bodge or temporary fix because that's just what they are, bodges and temporary fixes. Self-centring is vitally important for the stability of your car and your safety. If it doesn't self-centre something needs to be changed. Increased caster will do the trick but may not be easy for you to achieve at this stage in the build. It's a bit late to tell you this but using a combination of wide top clevises and spacers to move the top wishbone backwards or forwards you can arrive at the optimum caster.

I believe Escort or Cortina uprights give more self-centring than Sierra ones so if you are using Sierra ones that's something you could easily change.

all due respect back at you, I'm not self building a locost.

This is a tried and tested kit with hundreds sold. From time to time these cars fail on the self centering test. I'm fairly sure its due to still ball joints supplied by dax but want to do everything I can to alleviate the issue.

Because it is a kit its highly unlikely I need to start thinking about redesigning the wishbones or changing uprights.

Some manufacturers are renownd for having poor geometry and I suspect others posters assumed like me that it was one of them.

Have you possibly fitted the wishbones the wrong way around? Don't know about the Dax but some aren't symetrical and can fit the wrong way.
It can be caused by tight steering. Disconnect the track rod ends; Do the uprights turn easily? If not then it has tight ball joints; try working them around or try some new ones. I wouldn't try hitting them personally. If they're free then it could be the rack thats tight. You can reduce the presure on the pinion but be carefull not to go so far as the have play.

The spring bodge (and I don't advocate it) is to remove the track rods at the inner joint (not the track rod ends) and fit a suitable diameter valve spring behind on each side. It also restricts the rack so you get less lock. The testers are aware of this bodge and have been known to feel for springs under the boots.

adrian

quote:

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Originally posted by cd.thomson

Because it is a kit its highly unlikely I need to start thinking about redesigning the wishbones or changing uprights.

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I knew a guy who was building a |Rush and he had quite a thick instruction book and it provided details of all the suspension settings.

Have you got that, what does it say about the caster?

What's the stiffness of the steering components, any drag there will make the problem worse.

quote:

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Originally posted by interestedparty
I knew a guy who was building a |Rush and he had quite a thick instruction book and it provided details of all the suspension settings.

Have you got that, what does it say about the caster?

What's the stiffness of the steering components, any drag there will make the problem worse.

---

Hi

Just because it's a DAX doesn't mean that it has the correct castor. I've seen some down as low as 2 deg and some as high as 5.5deg when measured.
Get the castor properly measured. At least then you'll know where your starting from to give you an idea as to which course of action is required to correct the issue.

Oh and don't go smacking the ball joints with a hammer and drift. That will seriously shorten it's working life and may even lead to a failure if it's one of the pressed in together types.

Cheers Matt

Get it down to a garage and get them to set up the tracking - parallel tracking made an enormous difference to my car (it's still not wonderful though).
Good luck

Dave

Castor angle is where your wheel is like ashopping trolly backwards think of a merc or bmw front wheel tips to one side on lock putting wieght on edge of tyre thus making tyre want to return to flat surface other wheel has to follow because they are connected together try neg camber with some toe out have put 3 cars through sva none looked pretty but got them to self center problem with kits are they are light not enough down force what you are doing with incresed castor is buggering the handling but has to be done for test i run no caster on f27 turns in magic but bit liary on road how i like it Ali

Be aware that the IVA man is not expecting to see the car come back to 'straight ahead' when he lets go of the wheel! I was sure that mine was going to fail on this, but it passed first time. I asked him to show me what he was looking for and he said 'As long as it comes back a bit off full lock, it'll be ok'.

I had short bits of split fuel pipe around the rack ends, held on with cable ties which gave it a bit of springiness at full lock. They're still on there.
Now that I've done 2000+ miles in the car, the initial tightness of bushes and rack has all gone and I've got pretty good self centering.

So - don't go overboard, it's probably just tight bushes causing the problem. Give them a bit of 'help' with split fuel tube or some valve springs until it loosens up of it's own accord.

HTH,
Ed.

Oh, and of course make sure that your tracking is parallel and you've got sensible geometry first...!



[Edited on 9/8/10 by Madinventions]

I got my front suspension redone by Woszher, he remade the wishbones and set it up correctly. He did many kits too, just becuase someone has "designed" it - or should I say "badged it as there design" doesn't make it right.

Mine now self centre's like my tin top.

I wouldn't drive it if it didn't to be honest - there is a reason why every other car self centres.

quote:

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Originally posted by Madinventions
Be aware that the IVA man is not expecting to see the car come back to 'straight ahead' when he lets go of the wheel! I was sure that mine was going to fail on this, but it passed first time. I asked him to show me what he was looking for and he said 'As long as it comes back a bit off full lock, it'll be ok'.

I had short bits of split fuel pipe around the rack ends, held on with cable ties which gave it a bit of springiness at full lock. They're still on there.
Now that I've done 2000+ miles in the car, the initial tightness of bushes and rack has all gone and I've got pretty good self centering.

So - don't go overboard, it's probably just tight bushes causing the problem. Give them a bit of 'help' with split fuel tube or some valve springs until it loosens up of it's own accord.

HTH,
Ed.

Oh, and of course make sure that your tracking is parallel and you've got sensible geometry first...!



[Edited on 9/8/10 by Madinventions]

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At IVA we had a self centring problem which we attempted to fix on the day with toe in, we had already pumped up the front tyres.
Whilst the tester applauded our logic he did hint strongly that some toe out often helps, we did this, it did pass ( second attempt) . As with any IVA pass it is just that a pass we are now looking at getting the suspension properly setup

i say do what ever you need to get it passed, if you have to time, tools and skill to fix it then fix it.
if not then bodge away with valve springs and 'funny' suspension settings to pass then take the car to procomp or someone to get it set correctly, the SVA/IVA test is rubbish anyway, my car passed in less than 2 hours the tester said indys dont self centre so dont worry we revved the engine to 6k RPM for the emmisions test (should be 3k RPM) and a camber nut fell off on the way home and to top it all they let you drive a car you built in your shed or garage to the test centre and drive home if it fails

[Edited on 9/8/10 by afj]

I shouldn't be at all surprised if many of these 'no self-centering due to geaometry' problems are caused by tight steering gear.

So don't forget to check the steering components - disconnect the track rods and see if the wheels swivel easily. While the track rods are off, see how easy it is to move the mechanism by pushing on one of them - it should be fairly easy to spin the steering wheel. Finally, refit the track rods and see how easy it is to spin the steering wheel by pushing a road wheel from side to side.

You might be pleasantly surprised and find that there's an easy fix...

Found my self centering improved after changing the Sierra column bush for a self aligning bearing that allowed the column to rotate easier.

I had exactly the same problem.

Worth checking that it is stiffness in the lower ball joints causing it. Seems most likely, as the Dax geometry works normally, but can be susceptible to stiffness in the system. It seems the supplied ball-joints are particularly sensitive to installation increasing the pre-load and hence being very stiff - I had one that was, one that wasn't.

After consulting around, I reckoned my choices were to 'mechanically' relieve the preload using a big vice, press, or if brave a big hammer or send it back to Dax and get them to do it.

I risked the former, and it worked. If I'd broken it, I'd have been sending it back anyway...

Give Peter Walker a call at Dax - he'll have had a few calls about this sort of thing, I reckon! They may have a better solution by now.

Pete

Another approach would be to jack it up under the wishbones (so they stay level) and spin the steerign from side to side and see how it feels.

If its a bit stiff then disconnect the column from the rack and see how well the column turns on its own.

With a buit of investigation you should be able to either rule out drag in the system or loocate where it is coming from

Wow, long thread!

I should say that I'm not looking to cut any dangerous corners. I honestly thought self centering was only an issue for "ease of drive".

This weekend I'll get out in the garage and set up the geometry again as described in the manual, and see if I can loosen off the ball joint (as advised by Dax). How exactly did you manage that pete?

If it still doesn't seem to be sorted I'll investigate the toe-out option or consider taking it down to procomp.

The issues I'm having a largely financial with the car now. I'd never want budget cuts to result in a dangerous car but on the other hand I need to keep costs to a minimum now the car is "finished" as I'm only in work for 7 more days .

One of our club members has just gone through the IVA with his GKD Legend, He'd fitted a set of springs inside the steering rack and this worked a treat and passed that part of the test.

He's getting me a set of them to just to make sure I' get that bit right as well.

I'll post some pic's as and when I fit them

quote:

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Originally posted by locobri
One of our club members has just gone through the IVA with his GKD Legend, He'd fitted a set of springs inside the steering rack and this worked a treat and passed that part of the test.

He's getting me a set of them to just to make sure I' get that bit right as well.

I'll post some pic's as and when I fit them

---

Right do a search and yes, I do bang on about this.
Castor isn't just for fun!
When you drive into a corner, the feedback from the steering should be of that the wheel is trying to straighten again in your hands.
It is vital you get this right otherwise you are driving a dangerous car.
I've corrected my suspension by changing the top wishbone so that it is slightly further back than the bottom bone giving both my builds 7.5 degrees and changing the car from vague to ones that feel good out of corners.
The alternative is having to feed the steering back to straight ahead which is not only un-natural to most peoples driving but means you can't feel the road.
Springs, toe in, toe out, tyre pressure changes all work at low speeds, but when you are recovering your car from a ditch, don't say someone hasn't warned you.

Oh and trusting manufacturers to do this stuff? Some are still producing wishbones with no castor

[Edited on 9/8/2010 by nitram38]

quote:

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Originally posted by nitram38
Right do a search and yes, I do bang on about this.
Castor isn't just for fun!
When you drive into a corner, the feedback from the steering should be of that the wheel is trying to straighten again in your hands.
It is vital you get this right otherwise you are driving a dangerous car.
I've corrected my suspension by changing the top wishbone so that it is slightly further back than the bottom bone giving both my builds 7.5 degrees and changing the car from vague to ones that feel good out of corners.
The alternative is having to feed the steering back to straight ahead which is not only un-natural to most peoples driving but means you can't feel the road.
Springs, toe in, toe out, tyre pressure changes all work at low speeds, but when you are recovering your car from a ditch, don't say someone hasn't warned you.

Oh and trusting manufacturers to do this stuff? Some are still producing wishbones with no castor

[Edited on 9/8/2010 by nitram38]

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Nothing wrong with the Rush steering geometry from a self-centring perspective. There's plenty of castor designed in (9.5 deg measured on mine).

It's the initial stiffness (excessive pre-load) in some installed lower ball-joints that seems to cause the problems.

I'm not in the slightest bit "happy" about bodging.

U have U2U

quote:

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Originally posted by cd.thomson
I'm not in the slightest bit "happy" about bodging.

---

Just because some people fit springs etc to aid the self centering test during IVA, doesn't automatically mean their geometry is wrong. The springs etc are a sure-fire method to overcome initial stiffness in the system and only come into play at full lock. Previous posts are completely correct - during normal driving, it's the geometry that gives you the correct feel and safety factors. But, for the 'show a degree of self centering from full lock' test during IVA you sometimes need some mechanical help to overcome the tightness of new steering components.

Of course, it's imperative that every new build has a decent amount of time spent on it to get the geometry set correctly - it makes a huge difference to handling and safety. Get this right first and then think about springs etc if you still need them, (and your test/retest date is looming...)

Just my 2p's worth...

If you get enough castor then you shouldn't experience these stiffness issues. Often these cars have too little castor for road use coupled with new componants. Racing cars are slightly different in that they often use a bit less.

But if you have too much caster then the steering can get too heavy and you can start to loose the 'feel' that we all want from our cars. Also, the steering can tend to kick if you go over a bump, and changes to camber during cornering will also increase. As with anything, it's a compromise and once you're past the 'safety' aspects (ie. making sure it doesn't try to spit you off the road), a lot of it is down to personal preference - especially the differences between setting up for track days, or just for road use.

My cars is mid engined and I run about 5-6 degrees of caster and the steering is nice and light while still being positive and straight line stability is good. I've got rubber tubing on the steering rack ends but this only ever comes into play at full lock so has no effect whatsoever during normal driving. It just helps when parking etc.

Happy days
Ed.

Am I right in thinking correct "castor" would manifest itself with the upright sitting on a diagonal axis with the top of the upright closer to the rear than the bottom of the upright?

Just checking my wishbones are right

[Edited on 11/8/10 by cd.thomson]

The top should be further back than the bottom, like this.
Ed.

cheers ed! Simple enough.

Looks to be plenty on my car, so I doubt thats an issue!

Can anyone explain what effect caster actually has? Basic physics/engineering welcome. No point building a car if I don't learn something at the same time!

[Edited on 11/8/10 by cd.thomson]

Hi

I really can not believe that this subject is still coming up for discussion and argument . The fitment of valve springs in to the rack to aide self centering is not accepted by the IVA. If they find out they are fitted they will fail you.

Now if you have 5 deg of castor and geometry that is in the ballpark of being what the car would require to be driven normally it will pass the IVA without problem there should be no need to start setting the geometry up with way out settings just to induce self centering. What most are missing is that castor dose not just give you self centering that is only a small effect of what effect it has on the geometry whilst turning.

Now the problem here is that just about every one of the main kit manufacturers have such poor control of the jigging on there chassis that if you actually measure the castor properly you will find that they fall well short of what the manufacturers actually claim. Most only have 2-3 deg rather than the 5 deg than they claim. Then there's the problem that the jigging from left to right is also poor so you get differences of up to 4 deg across the car.

The claim that ball joints are too stiff is also a bit dubious. If a joint is stiff enough to stop a car with a genuine 5 deg of castor self centering then the joint is not usable and should be discarded because manipulating it to loosen up is only going to give it a short life span or worse case scenario damage the construction of the casing where it has been pressed over leading to it becoming possible to pull the inner ball out of the casing.

If you do not have the required castor for your car or application as there's a difference between a CEC and a BEC you are not just lacking the ability to have self centering ability you are lacking some of the basic geometry to control camber during cornering and with out it you will never have a car that will handel as it should giving positive feedback and feel. Illegally bodging it through the IVA test and ignoring the fact it is not right is also robbing you of having a car that is much more pleasurable to drive and more importantly helping you avoid situations that could lead to an accident.

If your kit manufacturer sells you a kit stating it has X amount of castor and you build it and find you are falling short of what they have stated and it does not allow you to legally pass the basic tests required to become road legal then you should be talking to you manufacturer and getting them to correct the problem FOC.
This all down to the very basic simple use of the jigs during construction whether that be on the chassis or the actual wishbones if they can not control the accuracies then quite frankly they should not be trying to produce the product and take your money.

Cheers Matt

Cheers procomp,

I'd just like to say, from my standpoint, now that I've been informed of the issues by very knowledgable people like yourself and nitram (amongst others) I want to do everything I can to check the geometry is setup as well as it can be in a home garage.

I've cast a glance over my caster on both front wheels and its definitely 5 degrees plus, more like 7-8.

OK! I'll add some fuel to the fire.
As Procomp says, if the IVA tester finds anything fitted to the rack to aid self centering, you will have a fail.
The steering on my Indy was very tight, I disconnected everything one step at a time, starting with the steering column, and ended up with the rack, an MK shortened Sierra item, having no lubrication whatsoever I fitted a grease nipple on the centre section and gave it large with the grease gun, can now spin the steering wheel with my index finger With the car on stands.

ill post this here rather than make a new thread (unless noone is reading!).

When sorting the geometry is there a specific order of things to do?

Should tracking come last/first etc?

Cheers guys, going to get stuck in tomorrow

Hi

Castor if adjusting.
camber
tracking

Assuming it's just the basics your setting up. IE not looking at bump steer etc.

Cheers Matt

thanks for all the help in this thread matt, much appreciated

Hi

I missed the obvious first step. Set RIDE HEIGHT. Ideally as it would be with driver on board.

Cheers Matt

really basic checks - this is how the wishbones should look

Anotated castor

A simple and cheap test of your castor using basic tools like this

castor 1

and from above should look like this

castor 2

You should have 22mm difference if using book suspension with Cortina knuckles

after spending a few hours twizzling track rods am I right in concluding that I can't accurately set up my tracking (toe-in/out) at home? I need some sort of two wheel alignment gizmo?

My manual says I need to do tracking/camber/tracking because its not possible to accurately set camber if your toe-in/out is wrong?

[Edited on 13/8/10 by cd.thomson]

You can do tracking pretty accurately at home, and all four wheels too.

What you need is a flat, reasonably level surface, four axle stands or similar, some good quality string and a decent 600mm steel rule and lots of patience and carefulness.

Adjust the height of the stands so that where you tie the string to them is the same height as the hubs

basically you need to get a taut string line either side of the car, then move them about until they are parallel, AND so the car is centrelined between them (do that by maing sure that the distance from each hub to the line is the same, but remember that the back axle might be different width to the front.

When it's all set up, you can measure from the front of each rim at string height to the string, and then the rear of each rim, and that will tell you whether your wheels are lined up properly or not.



The more careful you are, the more accurate

And remember to re-check the string placement each and every time you trip over the strings

[Edited on 13/8/10 by interestedparty]

found at least one part of the problem.

My lower ball joints are immovable .

Can just about get them to shift with a few whacks of a hammer but thats about it..

quote:

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Originally posted by cd.thomson
found at least one part of the problem.

My lower ball joints are immovable .

Can just about get them to shift with a few whacks of a hammer but thats about it..

---

yeah, not at all..

thanks have to go to peteS2K for pointing that one out.

I can't sort them out so I'm sending the wishbones off to dax tomorrow for them to fit some new ball joints.

Fingers crossed for a retest week after next.