Lotus Elan

Steering Rack Height

PostPost by: William2 » Wed Jan 08, 2014 4:07 pm

The steering rack loosely fitted to my Elan chassis has no shims on the mounting platform. The chassis has been powder coated by the previous owner so I cannot see any shim size marked on the chassis. Did Lotus tend to mark the shim sizes in black marker pen or might they have been stamped on in which case they might still be underneath the layers of paint?
When I refit the rack I am going to use some aftermarket solid alloy mounting blocks and I was wondering what the best method would be to position the rack at the correct height. I assume that the alloy blocks would be made to the same tolerance as the original Triumph fittings.
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PostPost by: miked » Wed Jan 08, 2014 4:50 pm

To do it right you need do "bump steer" settings and shim to the readings. Have a trawl on here and also on the net. Worth the effort. You can become confused by all the angles in the drawings but the actual basics are the wheels going up and down (from a set droop to a set bump) and staying in the foward plane. Some set in some toe on full bump but I think there are a lot of cars out there that are way out so if you get them neutral you are ahead of the game.

Make sure you equalise the alloy mounts each side and also check your track rods are the same length. Also the track rod ends are screwed on the rods the same amount before you start.

Mike :)
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PostPost by: Mr.Gale » Wed Jan 08, 2014 6:26 pm

I just went through this and with the help of Keith Franck I got it sorted out. At the beginning I made two videos that showed how I tested the bump steer (that I sent to Keith) so maybe it will help you get started.

1# http://www.youtube.com/watch?v=zOi9nDYre_A
2# http://www.youtube.com/watch?v=z72l1wGubNo

What I did was adjust the height until the lazer dot goes straight up from the X. It doesn't matter what it does below the X, that is droop.

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PostPost by: RichardHawkins » Wed Jan 08, 2014 9:30 pm

William,

Brian Bucklands book page 424 shows how to measure the shim thickness you need.

Brian shows a straight edge across and on top of the front wishbone mounting studs in front of the suspension towers. He states that the dimension from the bottom of the straight edge to the rack platform should be 158 mm.

Various authors on the net describe ways of measuring bump steer and how to minimise its effect. Many people have ended up with shims much lager than that given by Brian. Perhaps the original design intended a degree of bump steer?

My intention is to make shims according to Brian's dimension and shims to minimise bump steer. Then see if I can tell the difference when driving,

Brian's book is in my opinion well worth the money.

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PostPost by: au-yt » Tue Apr 15, 2014 9:54 pm

Hi Richard
I was wondering how you got on with the rack shimming.
Sadly I dont have a copy of the Brian Bucklands book...yet, The Dimension that is in Brian's book referes to rack platform should be 158 mm to the top surface of the upper control arm mount. I assume the is after the addition of the required shims?

I have used the laser bump steer method with some sucess and will use it to see what the steering does at that height. There is quite a lot written about bump steer, and there is some advocation towards a small amount of bump Understeer ie Toe out at the top of compression to reduce slip angles and understeer.

Regards
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PostPost by: au-yt » Wed Apr 16, 2014 9:09 am

Another Laser alignment method.
http://www.youtube.com/watch?v=LO07qmJ9zkk

Graeme
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