cd.thomson
|
| posted on 9/8/10 at 01:27 PM |
|
|
self-centering
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.
Craig
|
|
|
|
|
interestedparty
|
| posted on 9/8/10 at 01:55 PM |
|
|
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.
As some day it may happen that a victim must be found,
I've got a little list-- I've got a little list
Of society offenders who might well be underground,
And who never would be missed-- who never would be missed!
|
|
|
cd.thomson
|
| posted on 9/8/10 at 02:00 PM |
|
|
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.
Craig
|
|
|
interestedparty
|
| posted on 9/8/10 at 02:07 PM |
|
|
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)
As some day it may happen that a victim must be found,
I've got a little list-- I've got a little list
Of society offenders who might well be underground,
And who never would be missed-- who never would be missed!
|
|
|
adithorp
|
| posted on 9/8/10 at 02:20 PM |
|
|
quote:
Originally posted by interestedparty
Can only be increased by moving the top wishbone back (or the bottom one forward)
...or remaking the top wishbone so the joint is further back.
Higher tyre presure and extreme wheel alignment are just temporary fixes. As is sticking a valve spring behind each track rod... well thats more a
bodge!
"A witty saying proves nothing" Voltaire
http://jpsc.org.uk/forum/
|
|
|
cd.thomson
|
| posted on 9/8/10 at 02:27 PM |
|
|
I'm fine with temporary fixes.
Will a spring stay behind the track rod ends during driving?
Craig
|
|
|
2cv
|
| posted on 9/8/10 at 02:42 PM |
|
|
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.
|
|
|
cd.thomson
|
| posted on 9/8/10 at 02:45 PM |
|
|
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.
Craig
|
|
|
adithorp
|
| posted on 9/8/10 at 03:10 PM |
|
|
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
"A witty saying proves nothing" Voltaire
http://jpsc.org.uk/forum/
|
|
|
matt_claydon
|
| posted on 9/8/10 at 03:14 PM |
|
|
quote:
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.
Unfortunately that's not the case. For some bizarre reason, after 10 years or more, many of the kit manufacturers are still blindly copying the
Sierra front geometry thinking that it'll work the same with 250 kg on the front axle as it did with 500+. Sevens need more caster, and
it's about time the manufacturers designed their products properly instead of getting their customers to bodge the cars to pass the IVA.
I don't actually know the situation with Dax, TBH I'd have thought theirs would actually be a bit better developed, but there's
still no reason it shouldn't self-centre just because of tight ball joints and anything involving tyre pressure, extreme toe, etc is a bodge.
They can't be as bad as MK though, who have unbelieveably recommended on numerous occasions that people use valve springs in the rack!
|
|
|
interestedparty
|
| posted on 9/8/10 at 03:34 PM |
|
|
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.
As some day it may happen that a victim must be found,
I've got a little list-- I've got a little list
Of society offenders who might well be underground,
And who never would be missed-- who never would be missed!
|
|
|
Bluemoon
|
| posted on 9/8/10 at 03:39 PM |
|
|
quote:
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.
Can second that my MK self centering has improved over the first 1,000 miles... Check the caster in the instructions, and measure it if you can I
think you need about 7degrees for good self-centering in a 7 (I would hope Dax got the correct, they go on enough about there fantastic suspension
setup!)..
|
|
|
procomp
|
| posted on 9/8/10 at 03:44 PM |
|
|
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
|
|
|
panichat
|
| posted on 9/8/10 at 03:55 PM |
|
|
Before you do anything...
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
|
|
|
ali f27
|
| posted on 9/8/10 at 04:09 PM |
|
|
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
|
|
|
Madinventions
|
| posted on 9/8/10 at 04:15 PM |
|
|
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]
Mojo build diary: http://www.madinventions.co.uk
Solo music project: Syrrenfor http://www.reverbnation.com/syrrenfor
View my band website:
http://www.shadowlight.org.uk
http://www.eastangliankitcars.co.uk/
|
|
|
Dangle_kt
|
| posted on 9/8/10 at 05:26 PM |
|
|
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:
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]
|
|
|
snapper
|
| posted on 9/8/10 at 05:46 PM |
|
|
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 eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
|
|
|
afj
|
| posted on 9/8/10 at 06:59 PM |
|
|
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]
eerrrrrrrrrrrrrrrr
|
|
|
David Jenkins
|
| posted on 9/8/10 at 07:05 PM |
|
|
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...
|
|
|
rusty nuts
|
| posted on 9/8/10 at 07:21 PM |
|
|
Found my self centering improved after changing the Sierra column bush for a self aligning bearing that allowed the column to rotate easier.
|
|
|
PeteS2k
|
| posted on 9/8/10 at 07:27 PM |
|
|
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
|
|
|
interestedparty
|
| posted on 9/8/10 at 07:35 PM |
|
|
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
As some day it may happen that a victim must be found,
I've got a little list-- I've got a little list
Of society offenders who might well be underground,
And who never would be missed-- who never would be missed!
|
|
|
cd.thomson
|
| posted on 9/8/10 at 07:36 PM |
|
|
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 .
Craig
|
|
|
locobri
|
| posted on 9/8/10 at 08:20 PM |
|
|
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
|
|
|
.jpg)
