Lotus Elan

Steering Rack shims

PostPost by: haustrup » Sun Sep 19, 2010 11:06 am

Hi, I've read quite a lot regarding this on the Forum, as I find my Elan very "lively", but sometimes it's very difficult to understand as English isn't my mother language. Anyway, even at a simple point, it seem to me that I've found different answers to the same question, so I would kindly ask, which is correct.

It's often stated that the distance between the front wishbone pivot stud to the base of the steering rack should be 2.19 inches +/- 0.005.

But sometimes it's told as meassured from the center of the stud (which is a difficult meassuring poit) and sometimes it's told to be from the top of the pivot.

Which is correct?

Regards
Steffen, Denmark
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PostPost by: gerrym » Sun Sep 19, 2010 11:50 am

Steffan, there is no absolutely correct measurement: what you are trying to set is the amount of "bump steer"in the steering geometry.

Bump steer is simply the way the front wheel toe-in (or toe-out) varies as the suspension goes into bump or extension.

Search this forum under bump steer, and you will find a wealth of material.

Regards
Gerry
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PostPost by: rgh0 » Sun Sep 19, 2010 1:01 pm

The Brian Buckland Book quotes a dimension of 158mm from the top of the required rack shim to the top front suspenson spindle.

He shows a photo of a jig to measure this using a broad straight beam sitting on top of the top front suspension spindles with an arm and dial guage reaching down to the face of the rack mount. He says the dial guage is set to read zero at the correct 158mm distance and thus any reading is the thickness of shime needed. The reading is taken with the guage held at the 3 degree angle from vertical caused by the angle of the suspesnion spindles

Unfortunately Brian does not state if it is set to read zero from the centre line of the top spindles or from the top of the top spindle. He also does not state where the beam is located on the spindles and where the dial guage contacts the steering rack mount. Thus his 158mm measurement can only be used as an approximate setting and fine tuning by measuring the actual bump steer will probably be required.

regards
Rohan
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PostPost by: summerinmaine » Sun Sep 19, 2010 3:39 pm

gerrym wrote:Steffan, there is no absolutely correct measurement: what you are trying to set is the amount of "bump steer"in the steering geometry.

Bump steer is simply the way the front wheel toe-in (or toe-out) varies as the suspension goes into bump or extension.

Search this forum under bump steer, and you will find a wealth of material.

Regards
Gerry



Your point is well taken Gerry. Trying to set any adjustment to a "absolute correct measurement" is likely to be an exercise in frustration. Other than a reference point set as a datum (like the chassis height for snugging up the rear suspension fasteners), I always regard such measurements as a reasonable starting point from which to adjust the characteristic that you're attempting to achieve (or, in the case of bump steer, eliminate).
Jim

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PostPost by: Foxie » Wed Sep 22, 2010 9:33 am

Your point is well taken Gerry. Trying to set any adjustment to a "absolute correct measurement" is likely to be an exercise in frustration. Other than a reference point set as a datum (like the chassis height for snugging up the rear suspension fasteners), I always regard such measurements as a reasonable starting point from which to adjust the characteristic that you're attempting to achieve (or, in the case of bump steer, eliminate).

Couldn't agree more !

Check and correct the bump steer itself, not a "calculated" dimension one step removed :mrgreen:
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PostPost by: john.p.clegg » Wed Sep 22, 2010 2:31 pm

Couldn't agree more,as any alteration from standard weight/suspension-wise(5 speed box etc etc...) will alter the ride height and therefore the bump steer as this is measured +/- from the actual ride height...

John :wink:
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PostPost by: holywood3645 » Sun Mar 11, 2012 1:35 am

Assuming Brian Buckland measurment is a good starting point. (page 424 of his book) I have a question about a similar measurment from the top wishbone spindles to the top surface of the rack (when its installed) Does anyone know the measurment?

FYI: I have non-OEM alloy steering rack mounts and i'm a little concerned about the corresponding installed height be the same as the orginal mounts.

I already have adjusted to 158mm to from wishbones to rack mounting holes supports.

Thanks
James
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