Has anyone successfully removed bump steer on a MAC#1, MK, or other Locost?

My MAC#1 kicked to the right when I went over a hump at speed, so I suspected it was bump steer.

I've now put chassis on blocks at normal ride height, removed the front wheels, set up a laser on the brake disc, removed the coilovers and jacked the front hub +/- 20mm from normal position (20mm is full droop), so 40mm total travel at the hub. Then plotted the laser on a wall 1800 mm in front of the hub over the 40mm of movement. I think ideally I need a vertical line, but mine is approx 45 deg, basic trig shows the angle change at the wheel was 1.68 degs over the 40mm vertical movement. I think this is high. Then checking the steering rack knuckle joint position in relation to the plane made by the 4 inner wishbone mounts (just by eye) it looked like the rack needed to move down slightly to get the knuckle to sit in the plane. I then moved the steering rack backwards and down slightly along the chassis bracket, the laser test then showed slight improvement to 1.30 degs, better but still quite high.

I can't lower the sierra rack any further without removing ali material from the rack.

Any advice? I'm tempted to leave the rack in this "better" position and see how it drives. But guess I'll have to re-check and alter the toe angle as that will have changed if the rack is moved.

I cant help with your question completely, as i dont think i ever had an issue with bump steer as such on my Locost
But i did have handling problems, veering to one side, normally to the right and other anomalies

I transformed the handling, and i really do mean transformed! by altering the caster angle to 6% not the 5.3 it says in the book
I also used zero toe in/out and 7-10 % of neg camber also 17 psi in all the tyres

From a personal view, and i am far removed from being an expert, i believe a lot of the handling problems, are not actually handling problems, but lack of weight over the wheels, and these 7's and other kit cars weigh a third of the donor vehicle, well mine did !

steve

I believe the only proper way is to shorten the rack 4" according to the threads I found.

Moving the rack helps a little apparently but nowhere near as much effect as the the rack shortening :-


https://www.locostbuilders.co.uk/viewthread.php?tid=171091


https://www.locostbuilders.co.uk/viewthread.php?tid=173603

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I believe the only proper way is to shorten the rack 4" according to the threads I found.

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Have you checked the orientation of the track rod ends?

My memory is a bit hazy but I think I recall the orientation of the offset making a difference to my car. However it was a while ago so may be making this up...

I had to cut the rack mountings off the chassis,remove some material,and reweld them on so the rack is quite a lot lower to get my rack to sit level with the wishbones.
With it in the original position if I bounced the front of the chassis you could see the tracking changing on the wheels by eye