Lotus Elan

Bump steer correction

PostPost by: miked » Sun Feb 26, 2017 1:45 pm

I have just done this with the bottom Spyder air tank level (S4 Elan). The steering rack platform was not level and lower at the driver side. I did the two DTI method and ended up shimming the driver side by some 45 thou more than the extra added to both sides. Originally there was circa 100 thou each side, so not correct for an incorrectly placed rack platform. On the first test it was showing the correct symptoms on the driver wheel, as you would expect.
At the risk of opening a can of worms, this (IMO) makes the point that you can't rely on the rack shims, the only way is to test. Not the first time I have found this. Racks are usually too low giving a toe in on bump and toe out on droop.

Mike :)
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PostPost by: elanfan1 » Sun Feb 26, 2017 2:41 pm

And assumes the chassis dimension is correct to start with as many aren't.
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PostPost by: miked » Sun Feb 26, 2017 3:43 pm

true Steve. Also when you consider the various components that are involved in it being right, it is no wonder there is scope for improvement. M :)
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PostPost by: elj221c » Sun Feb 26, 2017 8:15 pm

miked wrote:At the risk of opening a can of worms, this (IMO) makes the point that you can't rely on the rack shims, the only way is to test. Not the first time I have found this. Racks are usually too low giving a toe in on bump and toe out on droop.

Mike :)


Does beg the question why Spyder supply the shims if they are not correct.

Must say that my ('82) chassis felt right straight away and have never felt the need to do bump steer checks.

Maybe their QC is not what it was?
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PostPost by: bitsobrits » Mon Feb 27, 2017 3:21 am

I bought a Spyder frame in '93, that came with shims which were correct to within a few thou based on a very careful bump steer check. Ran them as is, with no discernible bump steer.

Maybe Spyder is having a new employee/training issue.
Steve

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PostPost by: miked » Mon Feb 27, 2017 11:15 am

Chassis is from late 90's. I must say that the front bones were spot on and poly bushes went on a dream, like they do on Lotus ones. I have had trouble in the past with those. Don't know what to say apart from I have experienced issues in the past with inconsistencies. I am just making the point about checking is worth while if you are feeling some front end problems.
I had it under braking on a poor surface.

Mike :)
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PostPost by: greg40green » Tue Feb 28, 2017 8:48 am

I have completed bump steer checks on both my Elans , both running new original spec Lotus Chassis's.
Both came with shims that I presumed were pre measured to rectify any issues of bump steer once the car was built.
I suffered from bump steer with both rebuilt cars which was rectified by adding shim thickness after careful re- measurement .
My question is why the manufacturer pre-shim's a new chassis which is done I presume on completion of the building process to iron out any imperfections after fabrication if shimming/ measurements are not correct?

Even if supplied by Lotus or Spyder the measurements should be correct once put up for resale as most owners would be reliant on fitting the supplied shims presuming the measurements were correct.

Does anyone know who is now manufacturing the Lotus replacement chassis's as there's a rumour that they are being manufactured by more than one source.
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PostPost by: 661 » Sun Jun 11, 2017 2:17 pm

This is the only thread I can find with the 'double DTI' method. I'm sure I saw one a few months ago that had a link to a UK engineering firm selling them and they were cheaper than the Longacre ones.
Can anyone point me in that direction, please?
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PostPost by: 661 » Sun Jun 11, 2017 2:19 pm

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