Lotus Elan

Rack height for cranked bones

PostPost by: miked » Mon Aug 10, 2009 1:13 pm

Hi, I am progressing with a S4 FHC project car. I have the 26r TTR chassis and bones etc. I was having a look at the front and what happens with the steering rack when going through from full droop to full bump with the dampers out. I notice that the rack looks very low on full bump (acute rod end angles and the quite an amount of "toe in" steer from droop to bump). I have put the rack on with those alloy Triumph clamps. Is there meant to be a phyiscally higher alloy rack mount for the cranked front bones as these bones allow the ride height to be lowered more than standard bones. Forgive my ignornance.

Is this a TTR item, or is this how it is meant to be. I want to check bump steer, but thought this looked odd... :?

regards Mike
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PostPost by: miked » Mon Aug 10, 2009 8:40 pm

Got the answer. They are the same mounts. Too much travel with no dampers in. 1 inch droop and 2 inch bump from ride height for setting range approx', I am told. Sorted. Not forgeting that I now need to start taking reading and may well have to shim. Should be fun, not done it before.

Mike :)
Last edited by miked on Mon Aug 10, 2009 9:15 pm, edited 1 time in total.
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PostPost by: Old English White » Mon Aug 10, 2009 8:50 pm

miked wrote:Got the answer. They are the same. Too much travel with no dampers in. 1 inch droop and 2 inch bump from ride height for setting range approx', I am told. Sorted.

Mike


I love that kind of self-made posts . Very informative indeed .
We now have all the necessary space to comment , or change subject , etc ...
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PostPost by: bcmc33 » Mon Aug 10, 2009 11:19 pm

I'm sure TTR supplied the correct spacers onto which the rack mounts go. Just don't get them mixed-up.
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PostPost by: miked » Tue Aug 11, 2009 7:42 am

Brian,
Thanks. The chassis (only), although new, moved through someone else's hands and the shims were not there. I see the page from BB's book. I have checked that as a start point and only needed a 10thou shim one side to bring me to the 158 mm gap. I thought I would do that before taking any measurements

Thanks Mike
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PostPost by: bill308 » Tue Aug 11, 2009 9:38 pm

When I got my TTR racing chassis over a year ago, no shims were provided. It was a convoluted purchase because I ordered thru a second party and the chassis was picked up by a third party for consolidation into a container shipment. It's possible the shims were lost somewhere in the chain of events but always assumed I would have to do a bump steer process to dial it in.

Has anyone who has taken delivery of a TTR chassis been supplied with shims?

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PostPost by: batfish » Wed Aug 12, 2009 2:48 pm

I have not come across a new chassis with shims, I think it was something that may have been done when Lotus supplied the replacement chassis.

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PostPost by: bcmc33 » Wed Aug 12, 2009 3:53 pm

My car has an original Spyder stressed skin chassis and has shims under the rack. I can't imagine any of the previous owners having the slightet knowledge of this subject - so I have always assumed that the shims were supplied with the chassis.

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PostPost by: types26/36 » Wed Aug 12, 2009 5:08 pm

batfish wrote:I have not come across a new chassis with shims Andy


I thought that Lotus chassis's were supposed to have the amount needed (by shims) scribed on the rack mounting, I have never seen a chassis with such markings.......has anyone seen a chassis with this measurement on it?
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PostPost by: rgh0 » Thu Aug 13, 2009 1:58 pm

Neither the original chassis on my Elan or plus 2 came with any required shim markings on the chassis.
The replacement Lotus chassis I fitted to my Elan came with no markings and no shims

I have always had to set up the bump steer from scratch

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PostPost by: GrUmPyBoDgEr » Thu Aug 13, 2009 3:28 pm

For what it's worth; Spyder supply their chassis complete with the required shims, wired onto their respective mounts.

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PostPost by: gerrym » Thu Aug 13, 2009 6:39 pm

This post is in the racing section, so it has to be assumed that anyone setting up their steering bump steer will do it from scratch. Likewise suppliers of racing equipment such as TT will be making the same assumptions. Any factory supplied shims will in any case only be approximate (look at the tolerance build up not to mention individual preferences wrt turn-in). This post is a case in point, as different bone dimensions will cause different bump steer.

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PostPost by: cabc26b » Fri Aug 14, 2009 1:02 am

It would be pointless for the factory to guess the shims necessary, it assumes that all rack mounts are created equal , Ha, The last 3 type 26's i have done have had three entirely different rack mounts.

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PostPost by: miked » Wed Sep 09, 2009 1:20 pm

Update:

I had ago at the bump steer settings. I have not got the mag' to hand but I used the advice in the recent article in the Club lotus magazine. This was with two saw horses and some pieces of Ply and then some ally' straight edges on the discs.

I am not finished yet but pretty close. "Her in doors" (who must be obeyed) lifted me out. Been helping other Elan friend, so ran out of wife good will. :lol:

I made up some 10mm threaded rod adjusters to replace the shockers. Made a small clevis for the bottom shocker bolt and then fed the rod thru' the top hole. I used those shocker bottom rubber locator belled type washer and a flat washer (with a bit of oil) to centralise the rod in the top chassis leg hole. I then used the total shocker length for full droop ref' (fitted some lock nuts). Then, I figured that with the shocker fully bumped there is about 3 inch of travel, maybe a tad more. I then fitted more lock nuts. Gives a span. I also left a floating nut so this enabled me to run up and down the threaded rod from full bump to full droop. Droop, ride height (1 inch above), 2 inch above and then full bump.

Setting up your wood is a bit of pain with the saw horses on a poor garage floor.

I started with the little ally rack mounts and no shims. I had 8mm of toe in over the range of 3 inch travel (16mm in total). I shimmed until I am about 1mm total and have now gone to far with the last shim. Only on rough washers at the moment. I am quite chuffed with how this has worked. I am not near any small shims yet as I had to leave it, but can now start to zero in with proper shims. I must have about 6mm of shims under the mounts. The difference side to side is slight. The rack holes to the nearside are however out of line by about 50 thou,. You can see that the rack plate has been welded on, out of true and the track rod end angles show this from above. I will correct this.


Mike :D
Last edited by miked on Thu Sep 10, 2009 6:01 pm, edited 1 time in total.
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PostPost by: CBUEB1771 » Thu Sep 10, 2009 12:14 pm

types26/36/74 wrote:
batfish wrote:I thought that Lotus chassis's were supposed to have the amount needed (by shims) scribed on the rack mounting, I have never seen a chassis with such markings.......has anyone seen a chassis with this measurement on it?


As seen below, the required shim thicknesses are noted on my new replacement chassis sourced through Miles Wilkins. Also regarding cabc26b's comment about it being pointless for the factory to guess shim thickness; by far the the largest manufacturing errors are in the chassis, not the rack mounts. It makes a lot of sense for the chassis manufacturer to determine the rack shim thicknesses required.
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