pk
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| posted on 1/7/03 at 04:10 PM |
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Steering racks - bump steer
Using the “standard” escort rack results in a lot of bump steer. Does any one have a solution?
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Jon Ison
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| posted on 1/7/03 at 05:43 PM |
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mount your rack as level a poss with track rod ends when engine ect is fitted and car is settled on susspension
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Peteff
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| posted on 1/7/03 at 08:02 PM |
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I did mine with a mk2 rack and my theory was to get the track rods parallel to the bottom wishbones with everything built up. It seems to work o.k.
and doesn't give any problems driving.
yours, Pete.
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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kiwirex
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| posted on 2/7/03 at 09:04 AM |
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I'd suggest taking care with two points:
* track rod parallel with lower wishbone at ride height (works ok for cortina hubs, if your steering knuckle is higher, there are a bunch of alternate
theories in Alan Staniforths 'race and rally car sourcebook' )
* End of the steering rack, at straight ahead, should be in line with the two wishbone mounts.
Damn, needs a picture, hang on ...
Very primitive piccy attached (I think), with stylised upright on the right (if you can't tell). I've drawn top and bottom wishbones, but
no track rod. Steering rack to track rod join should fall in the grey area at straight ahead to minimise bump.
As above, track rod should be parallel with bottom wishbone.
Simplest choice if it don't fit nice is to shorten the rack.
Alternative is to move the wishbone mounting points. This could do heinous things to your suspension geometry affecting (primarily) camber and roll
centers (i.e. proceed with care).
cheers,
Greg H
 
Rescued attachment rackendpos.jpg
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pk
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| posted on 2/7/03 at 04:05 PM |
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bump steer
Thanks for the replies. My rack is mounted as the book – as near as I can tell! Although you only notice the problem when driving over pot-holes in
corners, it is a little disconcerting and needs to be corrected, if only for peace of mind!
The root of the problem seems to lie with the steering rack being longer than required. The distance between the track rod ends is about 22.5 inches.
That’s about 2 - 4 inches longer than required! I've been told that MK Engineering use a shortened rack from a Sierra. Now that I’ve splashed
out on a “quick” MK2 escort rack I’m reluctant the bin it.
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Jon Ison
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| posted on 2/7/03 at 06:05 PM |
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the easiest way to check 4 bump steer is bounce the front of the car up n down, you will see the wheels move in n out if you have bump steer, paying
attention to all the above will go a long way to cure it.
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pk
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| posted on 3/7/03 at 12:12 PM |
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Bouncing the front up and down reveals huge bump steer. It seems the best way to cure this is shorten my rack! Is this as easy as it looks?
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Viper
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| posted on 3/7/03 at 12:32 PM |
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Easy Task? depends on skilled you are and if you have the right equiptment to do the job.
Take a look at
http://forum.locostbuilders.co.uk/xmb/viewthread.php?tid=5974
might help.
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kingr
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| posted on 3/7/03 at 12:58 PM |
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If the bump steer is occuring when you're steering, I'm not sure there's an aweful lot that you're going to be able to do
since the pivot point will move depending on how hard you're steering. It's worth having a play about though, you might be able to lessen
the effects, I suppose, but you're always going to have it there at some degree of steering.
Kingr
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Ian Pearson
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| posted on 15/7/03 at 07:07 AM |
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I had my escort rack shortened by a local engineering shop when I first started out. There is a lot from the aussie builders about it on TOL, as ADR
are very strict when it comes to Bump Steer. If you look at the following thread, you'll get some usefull advice.
http://forum.locostbuilders.co.uk/xmb/viewthread.php?tid=6102
I spent ages on this, and now have no visible bump steer.
Regards, Ian.
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Rob Lane
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| posted on 15/8/03 at 09:46 AM |
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Bump steer is very marked on a standard steering rack. You can make it slightly better by re-positioning but it needs shortening to bring ends between
wishbone pivots. Trouble is that takes the
steering down tube closer in to centre of car and will interfere with engine unless modified.
it's even more marked with a quickrack and can be very unstable at high speed.
Sounds dangerous, but I take 'hands off' at speed and only make very very slight corrections keeping only a controlled light touch. Mostly
it will resettle back without any input. Worst are slow undulating roads that produce a wandering effect.
It's one of my winter projects this year.
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Rob Lane
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| posted on 16/8/03 at 08:55 AM |
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Dave,
You know what I mean 
If it's an open road, I'm never slow, just think I am. 
Bump steer on mine has been quite high since I built it, I just never got round to sorting it out.
I can actually see about 6mm of bump steer when car is set up on stands!
I've definitely got used to it and am constantly aware of it when driving on straight roads. Otherwise it doesn't cause a problem to
me.
It's one of those things to be sorted this winter, along with change of clutch and gearbox.
Both knackered after foolishly doing multiple 0-60 run testing using a Performance Meter. It was just too hard on drivetrain. Still, same thing would
have happened at the hillclimbs eventually with all the full power take offs.
Best time I got down too was 5.3secs 0-60 with wheelspin for first .5 sec that was useless energy according to run data. Most other runs were 5.5 ish.
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clubbie7au
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| posted on 24/8/03 at 12:04 PM |
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Bump steer
G'Day PK, You can eliminate all of your bump steer by removing 103mm from the LH end of the rack. You need to rethread the rack bar and screw
the tie rod / ball joint back in. I built 100mm wider and used a Mk11 rack. With carefull height positioning you can set it up perfect. Mine has no
measureable toe change 50mm either side of ride height and 2mm toe in at full droop. Hope this helps.
Regards, Mike.
Adelaide. Australia.
Mike @ The 'CLUBHOUSE'
Clubman Workshop. ;-))
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proper car
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| posted on 5/11/04 at 11:33 PM |
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why are you worrying about bump steer when you all use girls engines ?????
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Keith Tanner
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| posted on 17/2/05 at 03:57 PM |
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Here's a photo of the ideal rack width:
http://keith.miata.net/seven/flip.php?x=61
This is the rack out of an MX-5. I disassembled it and cut 5.5" from the center of the shaft. I didn't touch the threads on the end
because they're rolled, not cut. The case was given the same treatment.
The shortened rack:
http://keith.miata.net/seven/flip.php?x=6
Keith
www.slowcarfast.com
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