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Bump Steer
johnemms - 22/2/12 at 04:39 PM

Standard cortina hub & escort rack.

With the track rod end properly fitted (ball joint bottom - nut on top)
I got bump steer..

playing around - putting the track rod end upside down (ball joint top - nut bottom)
I significanly reduce bump steer however the taper is wrong...

Question:
Has anybody opened up the hole & fitted their track rod end steering arm ball joint the opposite way?
Or is this a case of whatever works - locost style?

cheers
jon


[img][/img]
[Edited on 22/2/12 by johnemms]

[Edited on 22/2/12 by johnemms]

rodgling - 22/2/12 at 04:45 PM

I have mine fitted this way (as per the GKD kit design). Don't see a problem with this arrangement if it gives the right results, but if you've built yours to a design that specifies the other way up then I'd try to find the root of the problem as something must be causing this.

tomgregory2000 - 22/2/12 at 04:55 PM

mine were fitted from above, but the car was designed to have them this way

britishtrident - 22/2/12 at 04:58 PM

Easiest way is to convert to rod ends (Rose joints) and get adaptors made up and the uprights machined. if you look up McGill Motorsport on eBay you will find loads and suitable dust boots.

Problem is your rack has M14x2 threads the solution is to find an Escort Mk1 rack with 1/2" unf threads



or Lower the rack.

[Edited on 22/2/12 by britishtrident]

daviep - 22/2/12 at 04:59 PM

I don't mean to offend, did you check bump steer over the full range of movement with the spring removed?

I can't help with turning the track rods, however I would have thought if you were to try and open the hole up you will probably end up with a parallel hole. I wouldn't be my chosen way of fixing the problem.

If your chassis is as per the book then the bump steer problems are caused by the steering rack being too long for the chassis. Shortening the rack and lengthing the track rods cures the problem.

Cheers
Davie

blakep82 - 22/2/12 at 05:09 PM

agree with BT, the steering rack is too high, lower it so its parallel with the bottom wishbones (or as new as) and the problem should be reduced til its not noticable.

the rack looks about the right length to me, so start with lowering the rack

[Edited on 22/2/12 by blakep82]

johnemms - 22/2/12 at 05:17 PM

Am getting ready to take the lot apart and lower the rack etc.... laser usual stuff..
But on a whim I turned the track rod end to the top and it looks to have cured it..

I have see some images of super sevens with the steering arms quite central and high..

procomp - 22/2/12 at 05:27 PM

Hi

As mentioned it's the rack that needs moving to get the right geometry. Also the rack does not need shortening. The LOCOST championship cars with the rack moved get the bump steer down to 16 tho.

But why do people keep trying to eliminate bump steer when in actual fact you want bump steer to aid geometry change during cornering to gain an advantage in grip levels.

Cheers Matt

Dusty - 22/2/12 at 05:54 PM

I think it depends how much bump steer you have. When I had built to rolling chassis stage I set the front wheels parallel by eye and could easily push the car. I then dropped in the pinto engine. The car could not be pushed back into the garage by two of us as the front wheels had turned in by about 20 degrees. The rack had to be raised about two inches and the wheels re-aligned before it was halfway reasonable.

blakep82 - 22/2/12 at 06:22 PM

quote:
Originally posted by johnemms
Am getting ready to take the lot apart and lower the rack etc.... laser usual stuff..
But on a whim I turned the track rod end to the top and it looks to have cured it..

I have see some images of super sevens with the steering arms quite central and high..


it won't have cured it as such, because you'll have moved a problem, the taper in the steering arms on the hubs won't match the taper on the ball joints now. what you will have done though is improved the angle of the track rods, which proves that lowering the steering rack is the answer

britishtrident - 22/2/12 at 08:36 PM

quote:
Originally posted by johnemms
Am getting ready to take the lot apart and lower the rack etc.... laser usual stuff..
But on a whim I turned the track rod end to the top and it looks to have cured it..

I have see some images of super sevens with the steering arms quite central and high..



That is because Ron completely skimmed over the issue of mounting the steering rack in the book --- just look at the original design for the rack mounting brackets.

The fact that Escort (or Sierra) rack is much too wide doesn't help the bump steer problem, bump steer completely robs the steering of precision particularly at turn-in.
These days narrowing racks is the usual route I have heard of MG Midget/AH Sprite racks being used because they are narrower but that creates the problem of mating 1/2" UNF track rods to Cortina or Sierra .

40inches - 23/2/12 at 08:46 AM

quote:
Originally posted by britishtrident
quote:
Originally posted by johnemms
Am getting ready to take the lot apart and lower the rack etc.... laser usual stuff..
But on a whim I turned the track rod end to the top and it looks to have cured it..

I have see some images of super sevens with the steering arms quite central and high..



That is because Ron completely skimmed over the issue of mounting the steering rack in the book --- just look at the original design for the rack mounting brackets.

The fact that Escort (or Sierra) rack is much too wide doesn't help the bump steer problem, bump steer completely robs the steering of precision particularly at turn-in.
These days narrowing racks is the usual route I have heard of MG Midget/AH Sprite racks being used because they are narrower but that creates the problem of mating 1/2" UNF track rods to Cortina or Sierra .


So MK got it right by shortening the rack.

johnemms - 23/2/12 at 12:08 PM

Steerin rack is quite low.. fitting the ball joint the other way round has given the best travel.
[img][/img]

MikeRJ - 23/2/12 at 12:44 PM

quote:
Originally posted by johnemms
Question:
Has anybody opened up the hole & fitted their track rod end steering arm ball joint the opposite way?


To invert the taper in the steering arm by reaming it out means the overall diameter will increase significantly (the smaller end would have the same diameter of the original larger end), so the standard T.R.E.s would no longer fit. You could perhaps fix this with a tapered sleeve, or an alternative ball joint, or a rose joint conversion.