Steering Rack Height - Help needed!

[Famous Frank]

I'm getting close to putting the body back on the frame. As a little background, this S2 Elan was hit very badly in the 1970's and poorly repaired. My friend Steve Smith of Twincam Sportscars in Sarasota, FL has a frame jig, and performed the frame repairs such as rebuilding the Left Front Strut, etc and also performed most of the 26R frame mods.

Now it's time to install the Steering Rack. I've looked at many articles regarding "Bump Steer". The easiest one to understand is in Brian Bucklands "Wonderful" Book on Elan restoration. His book asks for 158 mm from the wishbones to the Rack Mounting Surface, adjusted by shims under the rack. Here is my problem........The right side I have 159 mm clearance and I can insert one shim to get the required 158mm. But the left side I have only 156 mm clearance and that is with no shims. My question is how important is that 158 mm number? Is there a range to be in? Since I can't get the 158mm is it best to make the right side match the left side? Or any other thoughts on this subject?

Many thanks,
Famous Frank

[bitsobrits]

Frank

The most important thing is minimizing any significant steering effect as the suspension moves through its normal range of motion. I would first do an assembly without spring/shock and measure (with a dial indicator) the amount of left/right movement of the brake disc when moving the suspension about +/- 2" from ride height. You may or may not need any shims. I shoot for +/- .010".

If it turns out you do need to reduce the height of the "high" side, you can use aftermarket aluminum mounting blocks as available from several sources (or easily made locally) and have them machined a bit to reduce the rack height as required.

[GrUmPyBoDgEr]

Might I suggest doing a search for a posting by Miked.
Mike did a back to basics approach to measuring bump steer & made his own simple jigs to do the job.

A very worthwhile read & IMHO the oracle on this subject!

Good luck
John

[miked]

Hi John,

Thanks. High praise. It is at the bottom of this page. Hope it helps. I am about to drop the S4 FHC on the floor and will be using the bits again. Doh, pity I used one of the pieces to hang my space heater on. Mike

lotus-suspension-f42/laser-alignment-check-t20570.html

[Quart Meg Miles]

Thanks Mike for posting the link and John for recommending it, it's a stupendous idea.

The pictures don't appear on my screen but they copied to a file OK so I could see them. When my chassis was renewed (with galvanised Lotus) it wasn't stamped with any spacer heights so I'm going to fetch my saw to make that gauge.

[rgh0]

The easiest one to understand is in Brian Bucklands "Wonderful" Book on Elan restoration. His book asks for 158 mm from the wishbones to the Rack Mounting Surface, adjusted by shims under the rack. Many thanks,
Famous Frank

I dont have the book in front of me but are you measuring the dimension in the same way?. I may be wrong but If I recall correctly it was from the top of the lower pivot surface not the centreline ? to the top of the shim pack and if you are measuring from the centreline of the pivot you could end up with a negative shim amount like you have quoted.

In the end this is only a starting point and you really need to set it up using some form of bump steer measurement.

regards
Rohan

[Quart Meg Miles]

The easiest one to understand is in Brian Bucklands "Wonderful" Book on Elan restoration. His book asks for 158 mm from the wishbones to the Rack Mounting Surface, adjusted by shims under the rack. Many thanks,
Famous Frank

I dont have the book in front of me but are you measuring the dimension in the same way?. I may be wrong but If I recall correctly it was from the top of the lower pivot surface not the centreline ? to the top of the shim pack and if you are measuring from the centreline of the pivot you could end up with a negative shim amount like you have quoted.

In the end this is only a starting point and you really need to set it up using some form of bump steer measurement.

regards
Rohan

Buckland references from the TOP of the UPPER pin surface, not the lower pin. The lower pin is 208.3 mm (8.2") below the upper so the top of the shim pack would be 50.3 mm (1.98", probably originally 2.00") above the top of the lower pins. In view of the extensive repairs, Frank, perhaps you should check on the height difference between the upper and lower pins. The height of the rack above the lower pin will affect the bump more than the height to the upper one.

[rgh0]

I knew it was the top of one of the pins

cheers
Rohan