Steering rack???

[nomad]

I purchased a good low miles Spitfire rack and modified it to Elan specs. Now I am trying to set bump steer parameters and am wondering if the actual rack is the same length for the two. Was what I did possible or were there dimensions I overlooked?

Kurt

[bitsobrits]

I believe tie rod arm lengths are different. Elans are shorter. Should be some posts on this site about the specific differences.

[bitsobrits]

Just re-read your question. If you are you asking about the rack ball joint to ball joint distance, I believe they are they same.

Edit: Just found this. Rack shafts are the same. OEM rack was modified Herald.

https://www.macleansbridge.com/index.ph ... ring-racks

[nomad]

Thanks, folks.
The actual length of the rack is what I was interested in.

Yes , Chapman did quite a bit of modifying. With unequal tie rod ends and varying spacers inside the rack.

I am setting spacers for locating the rack and minimising bump steer. In reading one of Rohans posts he mentioned that the inner tie rod end balls should ideally intersect a line that runs between the upper and lower A frame inner pivot points. Seems logical but my car won't do that. Guess that is just the ideal and not what Lotus ended up with. Brian Buckland says set the rack mount at 158mm's below a bar ran from on top of the top pivot to the other so I guess that is my aim.

Kurt

[Elanman99]

Thanks, folks.
The actual length of the rack is what I was interested in.

Yes , Chapman did quite a bit of modifying. With unequal tie rod ends and varying spacers inside the rack.

I am setting spacers for locating the rack and minimising bump steer. In reading one of Rohans posts he mentioned that the inner tie rod end balls should ideally intersect a line that runs between the upper and lower A frame inner pivot points. Seems logical but my car won't do that. Guess that is just the ideal and not what Lotus ended up with. Brian Buckland says set the rack mount at 158mm's below a bar ran from on top of the top pivot to the other so I guess that is my aim.

Kurt

The tie rods (the link between the end of the rack bar and the 'track rod end' ball joint) should be the same length.

The spacers inside the rack are different lengths at each end (but they are not variable)

When you say that on your car you cannot yet the rack bar ball joints to intersect correctly, how are you measuring that?

The 158mm you mention might be the theoretically correct height for the rack but measuring it is another matter its easier (and better) to set the height for minimum bump steer as the front suspension is articulated over its full travel.(remove the damper and spring).

The bump steer topic has been covered many time on this forum (search for the Adamson method).


Ian

[nomad]

Thanks, folks.
The actual length of the rack is what I was interested in.

Yes , Chapman did quite a bit of modifying. With unequal tie rod ends and varying spacers inside the rack.

I am setting spacers for locating the rack and minimising bump steer. In reading one of Rohans posts he mentioned that the inner tie rod end balls should ideally intersect a line that runs between the upper and lower A frame inner pivot points. Seems logical but my car won't do that. Guess that is just the ideal and not what Lotus ended up with. Brian Buckland says set the rack mount at 158mm's below a bar ran from on top of the top pivot to the other so I guess that is my aim.

Kurt

The tie rods (the link between the end of the rack bar and the 'track rod end' ball joint) should be the same length.

The spacers inside the rack are different lengths at each end (but they are not variable)

When you say that on your car you cannot yet the rack bar ball joints to intersect correctly, how are you measuring that?

The 158mm you mention might be the theoretically correct height for the rack but measuring it is another matter its easier (and better) to set the height for minimum bump steer as the front suspension is articulated over its full travel.(remove the damper and spring).

The bump steer topic has been covered many time on this forum (search for the Adamson method).


Well,Ian, I put this rack together several years ago and for a US car the tie rods were unequal lengths. I've read several of the archived posts and agree that it would be best to set bump steer with shock removed and various methods for determining just what is happening as the suspension goes though its stroke. For a street car that seems an awful lot of work. Can you show me a simple method as easy as taking BB's advise?

[Elanman99]

To me trying to measure the 158mm sounds difficult to do but it will certainly get the bump steer very close.

Yes, taking the spring damper out is a lot more work but it only has to be once but it gets bump steer to its minimum value and takes into account any distortion in the subframe (chassis). For a road car getting the bump steer spot on is far more important than for track car.

The US car with unequal tie rods, by definition must have had bump steer. How unequal were they?

Ian

[bitsobrits]

Having built up several Elan chassis, and set bump steer to very near zero on each one, I cannot believe the tie rods are unequal on "US" cars. The car would be crazy/undriveable if that were the case. You've got something wrong if your rack is like that.

There is no quick and dirty way to set bump steer, and on an Elan you can get it very near zero only over about 2 1/2" of travel, so you first need to define the suspension geometry at the target ride height in order to define the center of the range where you will be working/measuring. Then mount the rack and start measuring and shimming. Using the stock mounts will get you close enough to get an initial measurement, but typically it will require shims in the range of 0 to 3/16" at each end (but not necessarily equal side to side) to get it spot on. I prefer the aluminum block type mounts, and have used them on my last few Elans as they eliminate the possibility of rack movement.

I use a single dial gauge these days for measurement as I find it easier than dual gauge setups.

This link might help you get started:
https://www.longacreracing.com/userfile ... _Steer.pdf

[Andy8421]

Just to be clear, its not that the tie rods sticking out the ends of the rack need to be exactly the same length, it is the installed distance between the centre of the ball joint at the end of the rack and the centre of the ball joint attached to the steering arm at the hub.

Given the considerable adjustment available when fitting the outer ball joint, it is quite possible to have tie rods that aren't exactly the same length, but have this compensated for by how the outer ball joint is fitted. Equally, it is quite possible to have two identical tie rods that have the ball joints fitted badly so that the effective length of the tie rod (ball joint centre to ball joint centre) is different on different sides of the car.

Before trying to set bump steer, the steering needs to be centred, tie rods the same length, tracking set correctly and the suspension at the normal ride height.

[nomad]

Steve, as you know this project has been languishing for a long time so my memory could be fading on this rack but as I remember one tie rod was a "cheap as chips" Triumph rod while one was a rather dear Lotus only part and as I remember a little longer. Could go look it up but it really doesn't matter since the final setting is what is important. I just thought the tie rods were logical since the rack itself is offset toward the drivers side. For geometry sake one does need things equal and I will be taking a close look at all of that. My mounts are hard urethane and exactly where that 2.5 inches of suspension travel will end up is only a guess. The Longacre bit is quite interesting but given how much I have left to do on this car and all the delays I keep running into I'm taking my chances with the lazy way out. Latest delay has been the GD weather!!!

Kurt

[snowyelan]

Hi Kurt,

My understanding is that, relative to the car centerline, the rack shaft isn't offset, the rack housing is. That's why there's different steering end stop lengths each side.

[nomad]

Hi Kurt,

My understanding is that, relative to the car centerline, the rack shaft isn't offset, the rack housing is. That's why there's different steering end stop lengths each side.

Of course you are correct, I should have stated that at the time I fitted the rack and without much thought on the subject thought it seemed logical. I now realize that the tie rod lengths need to be matched to center the rack shaft so I will have to have the long rod threaded nearly all the way in while the short one will have quite a lot of thead showing on its tie rod end. So i guess my next move will be to center the rack and then adjust the wheels accordingly.

Kurt