Bad Self Centering

[Guest Guy]

When I go forward in a straitish line then it seems to drive okay.

 

If I have the stearing wheel turned a lot and let go if it, insted of self centering it goes the wrong way and ends up on full lock . If I go backwards then it does things correctly.

 

I've played with the tracking but it seems to have no effect, any sugestions?

[Guest gordon_macnab]

Guy,

 

I had a similar problem with mine, one of the fail points on my SVA, it would self centre in reverse but not going forwards. There are a few areas to check.steering rack, tracking, tyre pressures, balljoints.

 

Dislocate the ball joints and see how freely the steering rack is. There shouldn't be too much resistance. I had to dismantle mine and give a rub down with emmery and a good grease up.

Get the tracking checked professionally. I had tried to do this myself but it was still a good bit out, plus they tracked it front to back also.

 

Check the tyre pressures this makes a difference too, it works better if they are a bit harder. I also fitted the original sierra wheels (175 as a pposed to 195's).

 

This all helped to make the steering self centre enough for the SVA, not brilliant but at least doing what it should, and with more miles the new ball joints etc have freed off a bit more.

 

Hope this helps

 

Gordon

[Guest Paul S Usowicz]

Guy

 

The tracking will have little effect on your car as the problem is your castor angle. The castor angle is what makes supermarket trolley wheels do what they do. On the Sub-K you have two options. The first is to move the anti-roll bar backwards and forwards (I suspect, like me, that your anti-roll bar never fitted and you had to drill new holes) or you can fit adjustable tie-bars (like I ended up doing). Your car as it stands will fail the SVA. Buy a castor gauge (£50 from Demon Tweeks) and work from there. Try moving the anti-roll bar as this is cheaper!

 

Look here for some more detailed info http://en.wikipedia.org/wiki/Castor_angle

 

Cheers

Paul S Usowicz

[Guest Guy]

Humm, interesting reading, here is a bit more info:

 

- My SVA is in 2 weeks ( )

- The stearing rack is new and is standard Sierra, it's not stiff

- the balljoints seem fine, not loose and not tight

- the anti-roll bar fitted fine with no modifications to it or the car

- the tyres are std Sierra 2.00 GLS (cant remember the size but probably 195)

- it seems to drive okay but with excesive deviation from the straight line (slow parking) the self centering works backwards.

- I've done nothing fancy with the build, it's all standard Sub-K just as it was intended.

[Longboarder]

As I understand it self centering is dependant on positive castor and steering axis inclination. You can't do much about the steering axis without getting too much negative camber so increasing positive castor to roughly 7 degrees by moving the anti roll bar mounting forward is your best option. Piccy below is how it should end up I believe. Something else worth checking is the camber of the front wheels. If they lean out at the top (positive camber) then there is room to move the top strut pivot inboard by ovalising the mounting hole till you have about a degree of negative camber. That increases steering axis as much as possible and helps self centering.

 

Nigel

[Guest Guy]

All very interesting, thanks for the replies.

 

Well it seems that the Caster angle has been blamed as the culprit

 

If I play with the bushes at the ends of the anti roll bar I'm sure I should be able to alter the caster angle, just as a point of interest, I didn't change the bushes, perhaps I should.

 

I'll measure the caster angle tonight.

 

Could the camber angle have any effect?

[Peter Bell]

Hi Guy, the camber won't have any effect on the self centering unless you have a huge amount. Look down on the top of the suspension, you should be able to see that the top ball joint slightly behind the lower one, if it is the other way around then you have a problem. Think of it a bit like the front forks on a motor bike. It is quite easy to measure approx. what the angle is by measuring horizontally from a vertical plane, (ie. piece of wood) standing upright to the centre of the bottom joint (with steering straight ahead) and then the top one. Measure the vertical distance between the two points and with a bit of basic trig. calculate the angle. I have about 3° on mine which to me is fine, light steering and self centering. Too much, and the steering is heavy. If you have time fit tie bars if not fit them later.

Good luck Peter.

 

 

Sorry Guy just realised you said it has mini mcpherson struts, so top ball joint doesn't exist but it will be subsituted by the strut top fixing bolt.

Will we see you at the Stevenage meetings one day?

Edited January 26, 2004 by Peter Bell

[Guest gordon_macnab]

Guy

 

Before moving the anti-roll bar position you need to look at the track control arm, It should be at 90 degrees to the centreline of the car if the set-up is correct if you move the anti-roll bar forwards or backwards you will change this angle and cause more problems. The track control arm position has been engineered to give the suspension the correct set-up, not just put anywhere.

 

If your still not convinced I'd get it checked by one of the tyre/exhaust places as they wil have the specialist equipment to measure all details correctly.

 

Gordon

[Longboarder]

Gordon, bit of a rock and a hard place situation here for Guy. Not enough positive castor means either bottom ball joint has to go forward with slight strain on the track control arm inner joint or the top strut fixing has to go backwards with some serious high quality safety related welding to do. I have seen lots of Hoods with slightly strained inner track control arm joints without hearing of significant problems although you would expect increased wear in the joint.

 

Nigel

[Guest Guy]

Well I measured the caster angle with some wood and a spirit level and got 9.7 degrees, I think this measurement is wrong.

 

If I make a temporary bracket for the top mount of the McP strut that I can adjust forwards and backwards then I can see the effect that it has on the car. I’ll do this and make a decision then.

 

I went into my local car shop this morning and they said that they can’t sell be a bush set, I have to buy a complete arm at £25 each.

[Peter Bell]

It is no good buying the arm you won't get the bushes anyway only the inner one. You want the compliance bushes on the anti roll bar, should be about £7? for the heavy duty ones. 'Heavy duty track control arm bush kit' is what is written on my last set. (The proper Ford ones are not very good). Which way was your 9.5°? with the top fixing forward of the bottom? have you measured both sides, you may find they are very different.

Peter.

[Big Jim]

Well I got radius arms complete with ALL the bushes for £12-50p each (possibly plus VAT, but can't remember)

[Guest Ianz]

Guy

Perhaps you should go back to basics,when I watched my video on how to assemble my series 3A Richard made apoint of emphasising the need to let the track control arm fall into its natural position before fixing the anti roll bar,to give the correct castor......maybe what you should do is to disconnect ARB,let the TCA drop and see whether the ARB is going to fit without moving TCA forwards or back,it may the be a simple matter of redrilling the mounting holes for the ARB brackets.

Just a thought.

Cheers Ian