Vague Steering

[Jonesy07]

I’ve been experiencing slightly vague steering, particularly after the car rises following bump/hollow on a straight section of road at 50-60 ish. I’ve checked bearings, track-rod end and the rack and all seem tight enough. Having read the item on the bulkhead bearing renewal I was wondering if this is the issue?

[phillpot]

Tyres or tyre pressures ?

Toe-in (or maybe yours is out)?

Shocks and/or springs?

[Roy C]

Steering column UJ's?

[techbotics]

IMHO check tyre pressure first.. 24psi on STD tyres

cheers D S3

[Barkychoc]

Check the rack is central - same amount of thread sticking out of both track rods - otherwise it tends to try and steer the car when you go over bumps.

Edited by Barkychoc on Friday 11th November 23:25

[Jonesy07]

Thanks for all the suggestions – will have a look over the weekend.

[TurboTony]

Barkychoc said:

Check the rack is central - same amount of thread sticking out of both track rods - otherwise it tends to try and steer the car when you go over bumps.

Edited by Barkychoc on Friday 11th November 23:25

Mine isn't, of course! 5 threads one end and ten at the other, but it needs tracking anyway. I am curious to know why this makes a difference (I am not questioning whether it is true). Can only guess that rack has some self centering?

[tvrgit]

TurboTony said:

Barkychoc said:

Check the rack is central - same amount of thread sticking out of both track rods - otherwise it tends to try and steer the car when you go over bumps.

Edited by Barkychoc on Friday 11th November 23:25

Mine isn't, of course! 5 threads one end and ten at the other, but it needs tracking anyway. I am curious to know why this makes a difference (I am not questioning whether it is true). Can only guess that rack has some self centering?

The rack itself does not self centre - the steering geometry (predominantly castor) does that as you drive along. As Barkychoc says, equal length are needed to eliminate bump steer.

When the suspension goes to full drop (say over a crest) the hub and wishbones on both sides drop by the same amount. Ideally, the track rod arm should be parallel to that movement through its whole range, but it's not - the ideal arrangement is compromised by the positioning of the rack at one end, and the track rod end at the hub end. The distance between the track rod ends is not the same as the distance between the centres of the hubs in any case - it can't be, else you wouldn't get the correct "Ackerman" angles (the outside wheel going round a bigger circumference than the inside wheel when going round corners) and the car would be almost impossible to steer except in a straight line.

Now, say the track roads are wildly different in length - when your suspension is on full drop, the shorter track rod will pull one wheel in, more than the other (because it's more different from the centre line to hub measurement than the other). The opposite will apply when the suspension is on full compression.

If it's bad enough, the steering wheel wobbles from side to side as the toe-in alters as you go over bumps.

I should add that there are various provisos attached to this, as the exact suspension geometry will vary between different car models, and some setups are more susceptible to bump steer than others. It's just good practice that you want to eliminate that as much as possible!

Edited by tvrgit on Saturday 12th November 13:57

[TurboTony]

Brilliant explanation! Thanks.