Steering rack shims

[millsn]

I recall seeing about shim to raise the height of a steering rack and reduce bump steer. Anyone got any experience of this? I may need to raise the height of my rack, is this a standard Caterham part or do you make your own?

 

Is this one?

 

Or is it this?

 

Edited by - millsn on 30 Dec 2011 17:21:55

[Richard Price]

I guess either of those shims will work, but you need to know how much you need.

It would be usefull to know how thick either shims are.

 

Optimising bumpsteer will depend on a few paramerters, so its best to measure your bump steer (over the full travel of the suspension, to get the full picture) and then add or remove shims to adjust the characteristic as desired.

 

If you've "upgraded" to exposed spherical bearing track rod ends, then it's likely that you'll need more shim than you have space to fit! Whilst they offer adjustment to bump steer, I've found that they start at worse, and get even worse as the washers are added!

 

When my car was narrow track I had 6mm under the rack, but now the car is wide track, I've ended up with 9mm of shim so that I get minimal bumpsteer around my chosen ride height.

 

It's also likely that you'll need longer bolts once you've got some shim under the rack.

 

 

 

[jj48]

Hi Millsn- have done several bump steer mods now and have found that raising the steering rack 6.5mm has alleviated the problem. You most certainly will need longer bolts and also check/reset the front wheel alignment.

Regards

Richard

[OliverSedlacek]

I've done this on a few cars now. There is no standard thickness shim that minimises bump steer, as if there was then Caterham would fit it on all cars. To get the best results, you need to measure the bump steer of your car and then keep adding shims until the bump steer is minimised. It's important not to overdo it as toe-in on bump is stable, but toe-out on bump is unstable.

[Paul Deslandes]

I wrote an article on how to measure and correct bump steer in Low Flying a few years ago, here. I've since added a footnote, which is included in the on-line version and describes a slightly easier method of measurement, raising and lowering just the suspension on one side rather than the front of the car. I needed between 8 and 9mm shims on both the occasions I did mine.

 

Its quite a laborious process and takes a few hours to do properly but is well worth the effort.

 

Blatmail me if you want any more info or clarification.

 

Paul

[millsn]

I'm actually only trying to raise the height of the rack. What I couldn't figure out was the actual part required to do so, then I saw the caterham comment (3 required per car on the second part I list and ordered three). My rack is too low and won't clear my oil filter. I don't think I mentioned bump steer originally but I have been looking for that article which I recall reading

[millsn]

Quick update. Having now fitted the three shims the rack clears the oil filter. I think I was having a moment as I failed to tilt the rack enough to allow the steering column to clear the oil filter in the first place.

 

I had mounted my horns to the lower xmember though so i had to butcher the shims somewhat to allow them to seat flat on the xmember. SO I now have steering and oil in the engine. Revelation!

 

Hopefully onto the electronic speedo conversion tomorrow and then to the MOT station