finally got the bump steer to near zero

[damo]

After a lot of head scratching and brain ache and 2 trips and $200 to pedders with how to correct the problem of too much bump steer, finally came up with a solution. It did involve making a bump steer tester out of some waste steel a couple of guages and a piece of white laminate wood. This tool is invaluable and I would thouroughly recomend making one. The key is getting the pivot point of the lower control arm as close as inline with the ball in the steering arm on the rack, and the ball in tie rod end level with the lower ball in the ball joint. This should ensure the steering arm is parrallel with the lower control arm therefore eliminating any bump steer.
I had to bend the cast steel stub axel 25 mm upwards to raise the connection point of the tie rod end.
Finally after just over a year now ready to put the body on and make some real progress.
Damo

[Rob. Smith]

Originally Posted by damo

After a lot of head scratching and brain ache and 2 trips and $200 to pedders with how to correct the problem of too much bump steer, finally came up with a solution. It did involve making a bump steer tester out of some waste steel a couple of guages and a piece of white laminate wood. This tool is invaluable and I would thouroughly recomend making one. The key is getting the pivot point of the lower control arm as close as inline with the ball in the steering arm on the rack, and the ball in tie rod end level with the lower ball in the ball joint. This should ensure the steering arm is parrallel with the lower control arm therefore eliminating any bump steer.
I had to bend the cast steel stub axel 25 mm upwards to raise the connection point of the tie rod end.
Finally after just over a year now ready to put the body on and make some real progress.
Damo

Damo...Did I read this right. You bent the cast steel arm that is connected to the stub axle. OOOh this is not a good move. The better way would to be to relocate the steering rack or box. Bending cast stuff is a very scary issue. It changes metal strength properties. The suspension bloke should have known about this. Pedders in Newcastle sold me a set of springs that made the car sit on the ground......no knowledge of spring technology just selling what they have. Please re think the bending issue.

[Rick Parker]

This is same method the BRE Datsun team did to the spindle arms on the Datsun 510's when they were being prepared for under 2 liter Trans Am back in '69 or '70.
The entire length if the arm was heated and bent while still applying heat, then zyglowed for potential stress risers afterwards.

Rob.Smith's recomendation of relocating the steering rack is a better idea given todays undestanding and technology. The above solution is pretty much the standard for Club racing and Auto X preparation given the general bugets available. Be safe. Have the part checked for underlying cracks.

[damo]

Thanks guys I know lowering the steering rack would have been a better option this was not possible without cutting the chassis. I guess I had better get the cast steel checked out. However I think having heated the steel to red hot and then bent it, may be ok.
Damo

[Legless]

Just came across this; it may be of interest to some.

http://www.youtube.com/watch?v=LO07qmJ9zkk

cheers

[400TT]

Excessive bump steer both front and rear is a pet hate of mine. Unfortunately you can just jack up some kits and visually see the bump steer on suspension droop.

It's a shame that not all states require bump steer to be verified for registration.

On our kits we have less than 1mm of bump steer at tyre diameter through full travel. Actually on some of the kits we can dial the bump steer so close to 0 that there is effectively no bump steer. That's both front and rear.

Just keep in mind bump steer will be affected by your caster changes. On all kits we have quick adjustment so that owners can dial front bump back to virtually 0 if they are running a custom camber or we can tell them the settings required for bump adjustment at a set caster. We also have bump adjustment on rear on most kits as well.

We actually check with the customer on their requirements and set caster and bump steer front and rear from the factory.

We use a bump steer jig like most race teams use. Big flat plate bolted to the hub with tracing mechanism on it. Once you get it close, you really need dial gauges to measure the changes.