My GTS Panther failed SVA on a few minors all of which (fingers crossed) are fixed bar the self centering.

My re test is on Friday morning

The self centering test was carried out as per the manual

'driving in excess of 10 mph and a degree of self centering should be evident'

basically drive slightly over 10mph and weave a little left and right whilst letting go and looking for a degree of self centering.

I know LOTS of you had your self centering tested in a different way but this is the way mine will be tested.

here is what i have done so far.

set the rack to centre and lined the wheels up by eye as a datum point.

i have moved the wheels over a few stages to reach toe out thats too bad to drive with - i can hear the tyres scrubbing and squeeling and you cant push the car for love nor money.

I have then wound it off back to my datum point.

then over a couple of stages i have wound it to toe in untill again i have reached the point where the tyres screech and scrub.

still not attempt at self centring.

all this is with soft tyres at approx 15psi

My column is free from snags, you can move the wheels by just gripping the column where it exits the footwell and turning so no excessive friction there.

My car is using sierra uprights and has no adjustment in the tophats to allow for castor adjustment.

Im struggling for what to try next and time is ticking.....................................................

any ideas?

Hi,

we thought we'd struggle with this but in the end we didn't. All we needed with the indy was a couple of turns toe out and highish (~30psi) tyre pressures. You could try increasing the pressures since this seemed to help us.

HTH and good luck with the retest

Ed

springs in the steering rack? just to get past SVA, then sort it after?

That's bad news - but I'm going to sound like a miserable sod here, and say that you should try and fix it so that you have decent self-centering WITHOUT any bodges or dodgy work-arounds.

The reason they look for self-centering is that it is A Good Thing that should be found in every car - it makes the car safer, easier to drive and could save your life (or someone else's). Dodgy fixes that get you through the SVA are not the proper answer - increasing the castor angle is probably the only real fix.

Sorry - but that's my view. I really hope that you get through the SVA, but you'll be happier if it's a proper pass.

David
(Good Grief - all of a sudden I'm getting serious... I need a drink to get over it!)

Sorry that I am going to say this, but remake your top bones with the correct castor.
It is the safest thing to do and once you start driving your car for real, you will appreciate how easy your steering will feel, especially when powering out of corners/bends.
Do a search, it has been discussed alot!

i deffo agree with these two ^ i was only saying springs because the retest is on friday. he's only got tomorrow to add more castor, whether it be by redoing wishbones, or brackets

Nitram,
They are GTS bones on a GTS chassis, and besides i dont have the time to make the bones before friday.

David,

I see what your saying and it would be somthing i would address post SVA when i have time to ponder different solutions etc.

Blakep82, there is no point putting springs in the rack as at no point during the test is full lock achieved.

It's worth saying that many of the SVA testers are aware of the tricks people use to achieve some form of self-centering - anything obvious and they'll just send you off with a flea in your ear, and tell you not to come back until you've done a proper job.

So, if you try any 'dodgy tricks', make sure they're subtle!

good point...

looking at you pictures in your archive, could you trim off some of the bushes in the wishbone tubes, and replace with washers (as spacers) to push the bottom wishbone forward, and the top wishbone back? don't think it would be enough of an adjustment though, but that combined with higher tyre pressures, as mentioned before?

i guess higher pressures reduces the contact on the road * and causes less friction, making what little effect there may already be, more noticable

* not a great idea to have less tyre contact witht the road though

just suggestions to help with the re-test on friday before sorting it properly after

I don't know much about gts bones etc, but I remade my top bones in 2hrs.
All I used was a sheet of mdf with some holes in to set the bushes up and I recut new material.
I don't know your set up or skills etc.
Are the top bones on the right way around?
What I will say is that the sva man might notice one of these get you through mods as they are now getting wise to this sort of thing.

As said above ^^^

Try to set the top wishbone back as far as you can, and the bottom one as far forward as you can, will help a bit. It might tip the balance for the tester.

Personally, I'd postpone the test and get it fixed - but that's your call and no-one else's...

There is NO adjustment in either top or bottom bone aside deom samber on the top one.

Looking from above the top ball joint is further towards the rear than the borrom one thus giving some deree of correct castor.

Possibly a set of adjustable mushroom adaptors would suffice if i can scrounge some before friday!

I wouldnt feel confident in measuring and making my own wishbones, especially in a rush!

col

15psi is way too low for self centering sva test

double it when you get to the sva station but dont let them see you do it

set a little bit of toe out before you go - youll scrub the tyres a little (unless you use the trailer again) on your way over but it using the toe out & high tyre pressures it should make an effort & get the pass you need

I haven't got as far as you, but I found it quite difficult to decide which way round the top wishbone should go - suggest you check.

It's quite easy to bend the top and bottom wishbone mounting brackets so you could try bending the top ones to the rear and the bottom ones to the front to give a little more castor.

In addition to that, as suggested above,
you could try skimming a bit off the polybushes on one side and packing the other side out with washers to bring the top wishbones back and the bottom ones forward.

Good luck, and let us know what happens.

We had this same problem some years back with using the Cortina uprights and book spec wisbones.

The top wishbones were remade with loads of castor (can't remember the actual figure) and it made not one jot of difference.

In the end applying a touch of Toe Out was all that was necessary.

IIRC part of the cause of the problem is due to the King Pin Inclination that is built into the cortina uprights (and not adjustable) that was designed around the weight of a Cortina rather than a 7 type car.

I know nothing about the Sierra set up, but wonder if it could be a similar issue that may be exacerbated if you are using a different offset of wheels than where used on the RWD Sierra?

The wheels in your photo archive look very FWD ish.

Drew

I was under the impression that it was better to lower the psi?

I will put it back up and try again with a bit of toe out.

I will be trailering it again, got my emissions within limits and i dont want to do ANYTHING that might mess it up!

Mac.
I dont really want to go trimming the bush (so to speak!) and i would advise against bending any of the brakets

I dont know if any other GTS'ers have had this problem, i suspect not as most of the other centres appear to conduct the test in a differnt way to how the book states.

I was fortunate that I had heard about this problem before I made my top bones, and was able to put in a decent amount of camber when I made them. I use Cortina uprights, and have more than sufficient self-centering...

As an afterthought - are you sure that EVERYTHING in the steering moves freely? All the ball joints, linkages, etc all moving easily? It's worth checking, to be sure that any tendency to self-centre isn't lost in stickiness somewhere.

Pretty sure everything is ok David

quote:

---

Originally posted by locoboy


My column is free from snags, you can move the wheels by just gripping the column where it exits the footwell and turning so no excessive friction there.

---

Jack up the front (both wheels together) and then try pushing one of the wheels left and right - you'll get some idea of what the castor geometry has to overcome! This is not too scientific, as doing this messes up the front geometry, but it is educational.

I'm puzzled about one thing - I've got a suspension book that says that having some toe-in makes the car more stable and thus it's easier to steer a steady course. It then says that having some toe-out aids cornering, but makes straight-line driving harder and more 'edgy'. But everyone recommends toe-out to help with self-centering - I'm confuddled...

[Edited on 22/8/07 by David Jenkins]

basicly

what i think you need is TOE-IN.

and a bit of caster.

sow in fact the front wheels are looking from the front and from above: / and

i think that as long as just both wheels try to win from each other the situ is perfect. problem could be that you need to set it up right for both the wheels.

every degree wich is not the same will result in unbalance. (one wheel winning from the other) and that will result in the car change ing from direction. also i think that you cant apply to much else the force needed to go back to its situ will be huge!! Sow basicly just give it a bit and look where it pulls to should be an easy job.

Tks

p.s. in my opinion i would give one wheel some degree wich i think is right! and then just correct it with the other giveing it more or less.

also the tyre pressure influences allot! on my daily tintop had a 0,8bar loss the car pulled to the right inmensily (it was the front right wheel)

On our Indy:

As the castor is pretty much fixed at this moment the answer is toe-out and higher pressures. On full lock the wheels tend to pull further into the turn using slight toe-in.

The SVA only tests the steering from FULL LOCK - self centring will be almost negligeable in the real world for most of the time.

IMHO - Get the pass and sort it after, if you're 'that' bothered!

Steve

quote:

---

Originally posted by Hellfire


The SVA only tests the steering from FULL LOCK - self centring will be almost negligeable in the real world for most of the time.


Steve

---

See HERE

for an explanation of how your wheel offset MAY affect the self centering action.

I think everyone under estimates the importance of King Pin Inclination (Or steering pin inclination) in the self centering action.

Drew

quote:

---

Originally posted by nitram38

quote:

---

Originally posted by Hellfire


The SVA only tests the steering from FULL LOCK - self centring will be almost negligeable in the real world for most of the time.


Steve

---

Negligible?
It is in use all of the time!
It keeps you from drifting about on the road and helps you unwind the wheel out of corners without having to feed the wheel.
I have tried my car with and without castor and it is a total pita without.

---

Hellfire, if you have the correct amount of castor for your car, you will get self centring across the entire turning circle, not just at full lock.
You are saying that it is negligible because lots of 7's only centre AT full lock? If so, this is wrong from a road driving point of view.
You will be amazed at how the correct castor will transform your steering.
It would seem a 7 trait that has not been corrected and keeps getting copied with each generation, otherwise this question would not keep on surfacing.
I think the new roadster book has dealt with this, but I am not sure.
Race cars have about 3 degrees of castor because drivers can put up with light "wandering" steering in short races as a trade off for "faster" steering.
Road cars have 5-7 degrees for relaxed, safer driving.
I have 7 degrees (rear engined though) and my car centres right across the entire steering range.
When I ran 3 degrees, the car would not attempt to centre.
lotustwincam, KPI does affect centring to some degree, but this is due to tyre scrub, where the KPI does not intersect the tread in the centre of the tire tread patch.
This can only be sorted by custom made uprights as the cortina/sierra setups have KPI for a McPherson strut.
Some of this is reduced by the correct wheel offset, bringing KPI closer to the centre of the tyre tread. (you can get positive and negative KPI too).




[Edited on 23/8/2007 by nitram38]

Hi Col,

to get you through the SVA, which is all your bothered about right now obviously, I would also recommend a couple of degrees TOE OUT and run High Tyre Pressures.

ATB
Steve

i had a lot of negative camber on mine when it failed. Straightened them up and lowered my tyre pressures to about 18 and it was fine.

(yep, i see people saying higher, but I incresed mine a lot on the way to the test center, and took it to a local car park. the car felt twitchy and I didnt like it so deflated them again before I drove to the test centre)

slightly contradictory to whats been said above, but I guess its a case of keep fiddling until you find something you like.

I'm with nitram on this one - a decent amount of self-centering makes driving so much sweeter. As I drive along I have to push the wheel into a corner, so to speak, and it'll tend to pull itself straight once I relax on the way out. You don't have to spend the entire journey aiming the car down the road.

However, that's not the point of this thread! Getting the man through tomorrow's SVA is the current aim - consensus seems to be:
1. up the tyre pressures - the car's being trailered, so it shouldn't be a problem for a while.
2. zero toe-in, or minimal toe-out - don't make it too obvious.

Once you've passed (fingers crossed) then I strongly recommend getting it sorted ASAP.

Good luck,
David

slightly OT but why aren't kits made to have an adjustment for the castor?

my formula27 - not built by me - has an angle brakect to which the lower 'bones brqckets are welded on and the bracket is held to the chassis via bolts in slots. This allows some to and fro movement and hance castor angle adjustment. (can't be done on top due to rocker arms)

Ok, so thinking about it, it is quite a heavy and non-elegant soloution but I had no self-steering problem.

I can't say I am that familar with 'bones and bushes but if the brakcets were made to be 10 mm wide and washers used to take up the space between the wishbone bush and bracket, then wouldn't that give adjusment, as well as allow for slight inaccuracies in construction?

(got me thinking that maybe I should do something like that soi save some weight....).

going back to the problem - can you remove the rearmost brackets and weld them a bit further back and use weashers/shims to take up the gap? Quicker & easier I would have thought than making up a set of top wishbones.

hi colin

pump your tyres right right up!!!!!!

this is why the less pressure in the tyres the more surface of the tyre touching the ground then the more harder it is for the tyre to be pushed out ie way to much grip

if you pump your tyre up the tyre raises from the edge inwards off the ground.


ta chris

Cheers Chris,

Steve,

It would appear that you have not read the whothe thread lol,

I said that my test is conducted in accordance with the manual,evidently not the way yours was.

The test involves driving in excess of 10mph, if anyone drove my car in excess of 10mph and applied full lock, the lack of self centering would be the least of their worries, the incoming punch on the chin would be furthe up on their list of problems!

The self centering test 'should' not involve full lock at any point hence my statement about springs in the rack too.

quote:

---

Originally posted by locoboy
Cheers Chris,

Steve,

It would appear that you have not read the whothe thread lol,

I said that my test is conducted in accordance with the manual,evidently not the way yours was.

The test involves driving in excess of 10mph, if anyone drove my car in excess of 10mph and applied full lock, the lack of self centering would be the least of their worries, the incoming punch on the chin would be furthe up on their list of problems!

The self centering test 'should' not involve full lock at any point hence my statement about springs in the rack too.

---

This all comes back to the same conclusion - if the castor is right, the self-centering works and the car passes the SVA. If there is insufficient castor, bodges are required, which may or may not result in a pass.

I know which option I prefer...

Right,

Tyres up to 32psi,

A small ammount of toe out, just noticable and it made a slight attempt to self centre on my narrow not very smooth road.

fingers crossed,

thanks for all your input and advice as usual guys.

Hope it goes well Colin - keep us all posted.

Just my two penneth - have you greased your ball joints prior to assembly? I noticed my Cortina uprights were very stiff and the track rod ends were too, resulting in a very stiff feel to the rack.

Mine still doesn't self centre despite having loads of castor, making hard work of town driving. I keep hoping it will get better with a few more miles on the clock but 8k miles later I am still waiting. tbh I don't see how it passed SVA

Raz,

Not greased the joints,

it has always been a surprise to me that there are never grease nipples on ball joints for everyday cars.

Fingers crossed and it should be MAC certificate tomorrow, then off up to Harrogate to see a mate of mine for a few beers before he flys back out to the states for another year.

how'd the retest go?

quote:

---

Originally posted by blakep82
how'd the retest go?

---

As it says in SVA thread -

Flew through emissions and self centering thanks to all you guys who have helped out and answered questions over that last couple of years.


Congratulations Loco