Strange Plus 2 steering rack

[miked]

Can anybody shed any light on this?

I have taken my Plus 2S steering rack out to clean and check etc and maybe change to a better one. I want to fit the alloy rack mounts and do my bump steer while I am working my way around the car.

I know that Lotus used the short rod Elan rack for the Plus 2 and fitted those end extensions between the rack and the track rod ends. My spare rack is one of those type. However the rack I have removed from this Plus 2S (1969) has no such extensions fitted. When I got it on the bench and removed the rubbers I found it has 50mm metal hex shaped extension blocks fitted to the rack thus moving the rod joints further outboard? Looks a proper job! In addition the actual rods are longer than the short Lotus Elan ones.

Is this something that a machine shop made up as a bespoke item or have any other people seen a rack like this? Is this a usual alternative?

One thing that comes to mind is that fact that the rod end are on a wider track. Have I read some were that this is a mechanical advantage when doing bump steer set up and that the use of the use of the Elan rack (with the extensions) was a compromise, anyway. I.E. It should have been a longer rack with shorter rods

Which on shall I go for? Also, any suggestions on obtaining packing shims and locking rings etc. The only site I have seen yet was Canley Classics with limited shim thicknesses.

Having done some reading I see that there seems to be a bit of variation on the ball end tension setting. The books saying 8Lb to move. Then Brian B's books saying just enough so as not move under own weight. This seems to be a lot of scope as 8LB is quite heavy at the end of one of the rods. Any thoughts appreciated.


Mike

[AussieJohn]

I have a feeling that the shorter rack with the longer tie rods are better re: bump steer, but I am happy to be shot down by others with more knowledge!
The tie rods have to be longer than a baby elan because the wishbones are longer on the +2 so the uprights are further out.
The hex pieces are the same as my 2 racks, maybe you have TR tie rods.

[elanman999]

Mike,
The basic rack on my Elan and +2 are the same. The difference is that the +2 has the extensions on the outer end of the tie rods. To me the rod joints should be in the same position for both cars as the inner wishbone pivots are also the same.
I would think that the long tie rods you have are standard Spitfire ones. The Elan and +2 (without extension) ones being about 1" shorter. The thread might need extending by rolling.
I have not seen any info on the length of the +2 rack being a compromise.
Does your rack have the travel limiting spacers? The dimensions are in the w/shop manual. These are easily made if needed.
Matty's keep (well used to) the rack shims, tab washers and near side bush.
I set the ball tension to the "book" but did set the pinion tension a bit lighter.
Cheers
John

[andyelan]

Hi Mike

The rack on my '74 Europa Special has 50mm hex spacers which sound similar to the ones you describe so my guess would be that's where the rack on your car is from.

The track of the Europa and Plus 2 is very similar so physically a Europa rack would fit, however, I don't think it would be a very good idea as far as steering geometry and bump steer etc is concerned.

Regards
Andy

[GrUmPyBoDgEr]

Hi Mike.

Geometrically speaking, longer track rods will have less influence on bump steer.
If I've followed your description of the rack in discussion the extension components extend the length of the rack rather than the track rods, which permits the use of the short Elan track rods, which I think will induce more bump steer, which may not be possible to dial out.
Theoretically the longer the track rods the less bump steer influence they'll have; something born out on modern race Cars, which have extremely short racks & long track rods.

Sounds like the job's coming along well
Cheers
John

[miked]

Thanks guys for your help and advice. A Europa rack, I never thought of that. Never touched one.

I will use the short Elan rack with the short rods and the Plus 2 rod extensions. As it happens I picked one up (off Ebay) about a month ago for ?15. It is a cracker. I dropped on. Maybe someone on here. If so, thanks.
Both racks do have limit spacer tubes to one side only. I will trial fit and check as the car has the bigger Spyder wheels fitted. When I did a quick droop to bump motion of the left side (after complete rebuild of that side) I did have a dramatic toe in on full bump. I was only going up against a piece of wood but it looked like about at least 1/2 an inch. The Europa rack must have contributed to this. I was always going to pull the rack and do bump anyway. I will reports back on how close I get the final setting.

Yes John, it is getting there. Seems to be a car the has lots of not to upsetting bits to do. I have quite bad gear oil leak that is dripping down the chassis. I think the motor is out next to do a box job. Whilst out I will tidy up the engine bay. Again nothing that dramatic but good benifit for a bit of elbow grease and a few bob.

Mike

[andyelan]

Hi Mike

Since I last posted I've had a look at the various suspension dimensions for the Europa and the Plus 2. From what I can see, altough the track on both cars is almost the same, the inner pivots on the Europa are set further apart so the wishbones are approx 2" shorter than those for the Plus 2. It make perfect sense therefore that the Europa rack has extensions at the inner end and uses shorter track rods while the Plus 2 has the longer track rod extensions.

Andy

[rdssdi]

Picture of my 1969 Elan +2 rack.

The "Hex Nuts" that secure the tie rod "ball and cup" are in rubber boot. I shimmed to spec according to workshop manual.

Bob
1969 Elan +2
1968 TVR Vixen
1963 Jaguar MK2 3.4

[alaric]

Hi, following the above posts, if the wheel moves up vertically by a distance x relative to the height of the steering rack, following a straight vertical path, then with the steering pointing straight ahead the distance between the pivot point at the inner end of the track rod and the vertical line is increased by a factor x/(2R), where R is the length of the rod. I get this from pythagoras and a binomial expansion. So, given the track rod does not change in length, the bump steer effect is inversely proportion to twice the length of the track rod. This is only a 2D approximation but gives the right idea I think. So longer track rods are a good idea. Also, making sure that the rack is at the centre of the vertical travel of the wheel puts you on the lowest gradient of the parabola, so for a given track rod length, will minimise the effect.

Sean.

[GrUmPyBoDgEr]

Reflecting on my earlier post the relationship of the track rod lengths & the upper/lower wishbones really should be as identical as possible so that all of the suspension components move up and down on identical radii, thus not invoking any bump steer.
That is of course in a geometrically ideal World.
I think that the wishbones are of unequal length & by applying the same theory produce more, desirable negative camber with greater suspension loading.
The proof of this would be to trace the Loci of the moving joints & takes us back to the need to getting the rack height correct via the shimming method.
I retract my statement about the longest possible track rods being the best solution because just like track rods that are too short, they will effect bump steer that may be impossible to dial out.
If I remember correctly, Len Terry's book on chassis & suspension design lays out the basic principles.

All a bit hypothetical since a wise member has pointed out the variation between the +2 & Europa rack & rods anyway

Cheers
John

[miked]

Thanks guys for all the input. Some pretty impressive thinking going on. So just keep to the little Elan rack with the Plus 2 extensions?

I just went into the garage for an hour and tried the ex plus two rack (I bought) into position. When it arrived there were no lock nuts on the extension pieces. I just found out why. When I built it up and set it in the car (with lock nuts) the thing was about 1/2" to wide. Took it out and removed the track rods. One is about 6.9 inch (had a chop, you can see the rough end) and the other is just over 7 inches (Spitfire/GT6 kit). I looked in BB's books and can see that I need the 6 inch Elan ones. It looks like some one had this on a Plus 2 but only by leaving off the lock nuts. Not recommended! Bit of a bummer, a Europa one and now a GT6 one. Not going too well. However the GT6 rack and pinion is nice and smooth, so not a complete waste.

Anybody got more spares than they need? I have posted in wanted also.
Either complete rack or just the 6 inch track rods.

Mike

[elanman999]

Mike,
If you are unable to get hold of any "Lotus" track rods I can extend the thread on yours(by rolling), this is provided the PO has not attacked the thread with a die. You can then cut them down to the length you need.
Cheers
John