Steering system self centring action

[bertvdmeer]

I have some problem with my 1986 Transformer Spidersport car. Recently the car failed a DOT safety test. The examiner found the car dangerous to drive. Basically if you put the car in to a turn and leave the steering wheel it will keep making turns, no self centring action whatsoever. Who had similar experiences, and what is the way to solve the problem.
Thanks
Bert

[guy mayers]

Hi Bert, the answer to no self centering is lots and lots of castor angle. The Fiat X1.9 uses about 9 degrees, much more than most cars so try shortening the leading link which will move the lower ball joint forward and increase the castor angle. Another possibility is a slightly seized or bent steering rack, make sure it is properly greased and moves freely. The final possibility is the intermedate shaft bearing block being too tight or not correctly aligned, try slackening the mounts and see if that makes turning the wheel easier. If it does then consider opening the hole to allow less drag, putting a thin washer between the two halves, greasing it or replacing it with a proper bearing (which means cutting and rewelding the intermediate column. I suspect you problem will be cured by more castor though! If you've always had stiff steering you'll be amazed how much more alive the car feels once you've got self centering.
Guy

[rutthenut]

Bert,

I would agree entirely with all of Guy's recommendations.

It is quite important to dial in as much castor into the front suspension as you can if you want to achieve any amount of self-centred steering. This can also have benefits in adding stability at high speed.

The problem is partly caused by the front end of the car being so light, so another - more complex - solution is to transfer more weight to the front of the car. Not the sort of thing to change with an existing car though.

With increased castor, turning the wheel effectively tries to lift the front of the car due to the suspension geometry. It is the downward weight of the car that resists this and tries to return the suspension and steering to the 'lower' position.

Shortening the effective length of the front tie-bars or leading links is easiest if it has rose-joint type joints at each end.

One other area of change that might make a difference could be to change to offset of the front wheels. Increasing the offset moves the contact patch of the wheel further from the point where the 'kingpin' would intersect the ground. This can lead to increased steering feedback - or kickback - but I couldn't say if that will help the self-centring affect at all. In fact that might improve if the steering had a 'negative steering offset' instead.

If you have a mind for experimentation, you could try fitting some wheel spacers to the front and see if there is any change in the behaviour of the car when the steering is turned and let go.

In any case, do try to set up increased castor if possible.

Also check for free steering rack travel by jacking up the car and ensuring that you can push the road-wheels from lock to lock (without the steering wheel lock being engaged).

If you can't get the steering to turn by pushing on an unloaded wheel, you should check the rack, steering column/bush and all ball-joints to remove the restriction.

The combination of these exercises should solve the problem for you.

[bertvdmeer]

Thanks Guy and John,
My car was set-up according to a specification given in a club Newsletter article from a couple of years ago. The article was entitled Suspension Geometry and was saying: "Here is the definitive picture as given by Chris Smith. He tells me that the car drove like a dream when the suspended like this. The measurements were taken with an Infrared Wheel Aligner´…………….. with the car empty sitting on 15 inch rims." The following table in the article mentioned a CASTOR of 4.2 degrees. I now really started digging and I found a personal note from Gerry when I changed my rubber bushes for nylon ones. He wrote down "as much caster as you can get", so this is inline with your remarks. I have already made a booking with a garage with a decent alignment tool and will try go for this max. I hope the wheel will stay more or less in the middle of the fender opening.
Bert

[rutthenut]

Originally posted by bertvdmeer
I hope the wheel will stay more or less in the middle of the fender opening.

You shouldn't find much of a problem with this, as the upper wishbone will not be moved and the short kingpin/upright length means that caster should change quite quickly with relatively small changes to the length of the tie bar.

[Arthur]

Hope this is of some use -

Allowing a very close approximation, if you check the wheel camber at 18 degrees steering angle left, then 18 degrees angle right, the difference in camber is the castor angle. (Positive castor, which is what we want for self-centre, makes the inner wheel in a turn go more positive camber).

The 18 degree figure isn't set in stone either, a couple more degrees won't make much odds, provided that you use exactly the same angles for each set of tests - I chalk lines on the floor and set the wheels parallel to them.

BUT .... you need a friend. If you own turn-plates you don't need to lock the wheels (car won't try to crab over as you put lock on), but if you don't, and who does? you will need a friend to heave mightily on the brake pedal to lock the wheels throughout the test or the car will indeed try to crab over, and bugger up any meaningful assessment.

Good luck, sounds like too much castor to me, second choice stiff rack, followed by stiff joints anywhere from the steering wheel down. (Allan Staniforth reckons you should be able to turn the steering wheel with the side of a finger with the road wheels clear of the ground - I've never managed to get one this light).

Arthur.

[bertvdmeer]

I solved the problem; it was a stiff steering system. There were basically three problems areas, from the steering wheel downwards:
Intermediate shaft-bearing block
The bearing block was rubbing against the welding of the fixed universal joint. Basically not enough play of the block or movement towards the steering wheel. I made a part of the hole in the bearing block much larger at the rack side.
Bulkhead crossing
I made myself a very sophisticated bulkhead crossing watertight construction. This contraption was made in order to keep rain water out of the car and to keep my feet dry. One of the fixing bolds of the universal joint (Fiat to rack) was too long and was rubbing against metal parts of this contraption. Shortening the bold solved this obstruction.
Steering rack
My car is a left-hand drive. So, at the right hand side of the rack a small nylon pin is installed in a hole in the rack tube on the location where the original mounting bracket is/was situated. The pin is there probably to prevent the rack from rotating. Garry's steering rack mounting block will push the pin against the steering rod and effectively create a large friction point. I drilled a hole in the mounting block at the location of the nylon pin. This removed the obstruction and effectively restored the original function of the pin i.e. prevent the rack from rotating.

The steering system is now ok. I have set the castor at its maximum (5 deg). The car past the DOT test and is now legally on the road.
I hope my English was sufficient enough to the explain the problems.
Bert

[vojx]

Originally posted by bertvdmeer
TThe article was entitled Suspension Geometry and was saying: "Here is the definitive picture as given by Chris Smith. . . CASTOR of 4.2

To add my (late) two cents worth, is Chris talking of a Corse or a Transformer? My Corse works best with about 4 degrees of castor, more is far too heavy, less is too skittish.