Lotus Elan

Steering Rack Height

PostPost by: ivan.wood » Sat Jul 07, 2018 9:39 pm

I have read on some previous posts that the steering rack mounting plate should be 158mm measured from a straight edge across the upper pivot pins, however mine is 153.7mm on one side and 154.5mm on the other. I don't understand how it can be 4mm out?

Has anyone else had this problem?

Thanks

Ivan
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PostPost by: billwill » Sun Jul 08, 2018 12:07 am

I understand that steering rack height has to be adjusted with shims to minimise bump-steer.
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PostPost by: rgh0 » Sun Jul 08, 2018 1:22 am

The measurement of 158 mm is quoted in the Brian Buckland book. However he is a little vague as he does not specify whether it is from the top of the top front spindles or the centre line of the spindles. He shows a photograph of a special jig he uses to measure it but that uses a permanent dial gauge setup and does not show the basis for the 158 mm dimension.

The steering rack support bracket is deliberately fabricated to low so that shims can be added to bring the rack up to the correct height. Requiring 4 mm of shims would not be abnormal.

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PostPost by: ivan.wood » Sun Jul 08, 2018 12:24 pm

By my reckoning if it is already 4mm less then adding shims will just make it worse?
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PostPost by: rgh0 » Sun Jul 08, 2018 12:52 pm

ivan.wood wrote:By my reckoning if it is already 4mm less then adding shims will just make it worse?


Sorry I miss read your post I though it needed 4 mm shims not it was 4 mm to close. Thats a much greater problem

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PostPost by: ericbushby » Sun Jul 08, 2018 1:58 pm

Hi Ivan,
Can I make a suggestion, this is how I checked mine.
Raise the car on blocks so that it is straight and level.
Assemble the front suspension without the springs.
Clamp a piece of wood to the lower suspension arm to act as a handle so that you can lift and lower the suspension throughout it`s range.
Fix a laser pen to the hub, I just jammed it in the hub centre with a piece of foam. A clothes peg will hold the button down.
Set up a piece of cardboard a few feet away, with a vertical line drawn on it.
Now you can see how much the wheel hub turns as you lift the suspension and which way.
The laser will show a slope away from vertical as the wheel hub turns.
If you now add shims under the rack mounts we hope it will improve and go nearer to zero and then you have a result.
If it goes worse there is a problem there, but I hope that is unlikely.
Reading this back it sounds complicated, but it didn`t take me very long to set up, and it will confirm where the problem is.
Best of luck
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PostPost by: ivan.wood » Sun Jul 08, 2018 2:06 pm

I was wondering if anyone else has had this problem as the bracket looks slightly damage but not enough to account for the -4mm difference. The bracket is basically level with the top of the cross member vacuum box and looks original?

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PostPost by: ivan.wood » Sun Jul 08, 2018 2:12 pm

Thanks Eric. I am in the process of putting the suspension back on the frame after a complete restoration and was checking the measurement before putting the upper suspension arms back on when I found the problem. I guess I will have to do as you suggest once it is assembled.

Thanks

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PostPost by: RichardHawkins » Sun Jul 08, 2018 9:02 pm

Ivan,

I have just checked Bucklands book, and he shows a photograph of a straight edge with a dial test indicator attached. The straight edge is resting on the top of the of the upper wishbone chassis pivots. Apparently this device was used to measure the rack height with the dial test indicator set so that the indicator reading was the shim thickness in units of 0.001's of an inch. Probably because that was the common unit on a dial test indicator used in the 1960's.

I used a method of checking bump steer as described by Eric, and after many niggling problems and much messing about I found that minimum bump steer required shims of about 5mm. Don't despair until you have checked. I also found that I could not measure any change in bump steer with a change in shim smaller than 0.5mm. I have read other reports of people using shims much thicker than Lotus specified. I don't understand where such a large discrepancy comes from. Perhaps Lotus designed in an amount of bump steer, and as my car is a long way from being finished, and I am not a good driver I may never know.

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PostPost by: NickD » Sun Jul 08, 2018 9:32 pm

I've seen a figure of 2.190" (55.63mm) quoted as the height of the rack platform above the centreline of the bottom wishbone spindles. The workshop manual shows a vertical distance of 8.2" (208.28mm) between the bottom and top wishbone spindle centres, which gives 6.01" (152.65mm) between the top wishbone centre and the rack platform, or 159mm from the top surface of the top wishbone - which is close to Brian's figure.
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PostPost by: ivan.wood » Mon Jul 09, 2018 12:20 pm

I guess if most cars need shims (hopefully around 4mm) then my steering rack might be about right without shims. I will have to do the bump steer test once I have the car re-assembled. I bought solid mounting blocks from Spyder so may have to machine them down.

Thanks for the feedback.

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