Thread: Bump steer

zero castor and loose swivel preload.

cheers phil

Originally Posted by discowhite

zero castor and loose swivel preload.

cheers phil

Did it get worse after the spring lift?
The diff rotates slightly changing the castor angle.

Bump Steer Explained - Circle Track Magazine

What causes bump steer is poor suspension geometry. It evident as the wheel travels up and down and the geometry causes the wheel(s) to steer.

On race cars a lot of work is done to eliminate bump steer. On a Land Rover it is inevitable because of the steering mechanism necessary to have a live front axle. It is at it's best when the steering linkage from the steering box to the left front wheel is parallel with the axle. Obviously the drag link is always parallel so the right front wheel hitting a bump will cause little bump steer.

Lifting a vehicle with a live front axle will only make it worse.

Definately lifting any live axle vehicle makes it worse, but Gq and GU patrols left the factory with it

I would pay close atention to the front radius rod bushes, replace with genuine rubber ones, and make sure that includes the ones at the rear of the arm where it attaches to the chassis.

I have found this has cured a few in the past. It is difficult to control a heavy item like a differential assembly after hitting a series of bumps etc when the bushes are worn or damaged.


JC

Bump steer is mostly caused by the drag link (from the steering box to the first hub) being too far out of parallel with the panhard rod.

My POS (50mm lift RRC) does it a little bit but it no longer wants to keep on turning (symptom of loss of caster angle due to lift........shopping trolley effect) because I've corrected the caster angle by rotating the swivel balls.

With a 50mm lift you will have 0 or slightly negative caster, should be about 3 degrees.

Search on here re: caster and you decide the way to fix.

cheers, DL

As indicated, bump steer is caused by imperfect steering or suspension geometry where a bump causes a steering effect.

No steering/suspension is perfect, but most manufacturers these days manage to keep it to a minimum.

In the Landrover solid axle/coil setup, three effects can be separated.

If the drag link is not parallel to the panhard rod (and the same length), and with matching pivot points, the sideways movement of the axle and the steering arm will not be the same when the LH wheel hits a bump. This is not a problem in the standard setup with the wheels straight ahead. With wheels not straight ahead, it is not a serious problem because the greater the turn, the slower you tend to be going. With a raised suspension, it may be worse because of poor design of the new drag link and panhard rod. (or keeping the old!)

The second effect is the turning movement of either front or rear axle when a bump is on one side only. This is inevitable with radius links of any kind, and is exacerbated by a suspension lift which means the neutral position of the link is further from horizontal.

The third effect is where, when a bump hits one side, the suspension bush at either end of the radius arm or lower link compresses in response to the bump in a way that allows the effective length of the arm to change. The original setup uses this effect to counter the second one, as part of the detail suspension design, but this compensation is affected by the installation of non-standard flexibility bushes or the bushes being worn or loose.

John

Near impossible to eliminate bump steer on a beam axle. Only way I know is if you can accomodate one of those steering boxes that had two pitman arms that steered one wheel each with no direct connection between the two wheels. These were used on some farm tractors long ago and the occasional pre-war race car. Next best thing is a rack and pinion system where the steering rods are connected to the centre of the rack not the ends. This gives two equal length steering rods with again, no direct connection between the wheels. These were found on early 50's Morris Oxford and Holden Camira. With this system any bump steer is from the length of the steering rods. Some speedway cars mounted a rack and pinion system on the axle with a U-jointed steering column to cope with axle movement.

Anyone wanting photocopies from the GM Goodwrench Chevrolet Power Catalogue Chapter 9 Vehicle Dynamics can PM me with their postal address. I don't have scanning facilities. Or, alternatively, I can post to someone with a scanner and they can post it here as a sticky.