02GF74
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 posted on 18/1/06 at 09:36 AM |
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steering rack position?
At the moment I amd taking apart more than is being put together 
I have moved the steering column back a bit so the uj link is too short. One solution is to move the steering rack back and this is what this post is
about.
What is the proper position for the steering rack?
At the moment, looking from above, the track rods poiont backwards. I would have expected ideally they should be perpendicular to the axix of the
chasis i.e. point straigh outwards.
Looking from the front, should they be horizontal, point up or down?
Been told that the wishbones should be horizontal so I would expect the track rods to be horizontal as well.
If I moved the rack back, the track rods may end up point forwards a little bit and also may point downwards, is that going to be a problem?
Looking at pictures in RH brochure it doesn't appear to be unless they have not set up their front end properly.
thanks.
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muzchap
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| posted on 18/1/06 at 09:41 AM |
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Hi mate,
I was told they should all be level, if not the track end rods pointing slightly down.
My chassis came pre-welded - so feel free to have a browse.
My 'mushrooms' are wrong hence the awful camber, but this is a good pic to show where the steering rack should be ;-)
PHOTO
It will all end about level when I adjust everything properly ;-)
HTH
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02GF74
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| posted on 18/1/06 at 09:50 AM |
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you've got extensions on as well!
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rusty nuts
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| posted on 18/1/06 at 10:20 AM |
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But isn't the Velocity wider?
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02GF74
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| posted on 18/1/06 at 11:52 AM |
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sorry, one more Q.
Four M8 bolts will be strong enogh to hold the steering rack in place?
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muzchap
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| posted on 18/1/06 at 11:54 AM |
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I have got extensions on... You need them with an Escort Rack....???
The Front End of the Luego is a BOOK CHASSIS....
Yup that's what I've got... 4 M8's with washers either side... and some 'threadlock' ;-)
[Edited on 18/1/06 by muzchap]
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rusty nuts
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| posted on 18/1/06 at 12:01 PM |
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It may be a book chassis but I think you'll find the track is wider unless it uses shortened drive shafts as in the Luego Locost IRS. Wishbones
are longer than book?
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britishtrident
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| posted on 18/1/06 at 12:09 PM |
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Viewed from above the outer Track rods should be slightly ahead of the rack --- just look at a Sierra, Mk1/2 Escort, Capri, Avenger. The reason for
this is it the way cars with rack and pinnion steering get any ackerman angle ie. toe-out on turns.
Putting the rack head of the outer track rod ends will give toe-in on turns leading to poor turn in and very iffy handing.
[Edited on 18/1/06 by britishtrident]
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02GF74
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| posted on 18/1/06 at 12:28 PM |
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quote:
Originally posted by britishtrident
Viewed from above the outer Track rods should be slightly ahead of the rack --- just look at a Sierra, Mk1/2 Escort, Capri, Avenger. The reason for
this is it the way cars with rack and pinnion steering get any ackerman angle ie. toe-out on turns.
[Edited on 18/1/06 by britishtrident]
ok, so moving my rack back is a bonus then!!
So like this when viewed from above:[img][/img]
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eddymcclements
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| posted on 18/1/06 at 01:55 PM |
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Good stuff on Ackermann here:-
http://www.racecar-engineering.com/images/features/ackermannpt1.pdf
and
http://www.racecar-engineering.com/images/features/ackermannpt2.pdf
and
http://www.racecar-engineering.com/images/features/ackermannpt3.pdf
Cheers,
Eddy
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MikeRJ
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| posted on 18/1/06 at 03:25 PM |
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Note that moving the rack will affect bump steer. When using a rack not designed for the chassis and suspension, moving the rack back/forward up/down
can tune out most of the bump steer. Just moving it randomly in one direction could make it worse, so I would definately want to be testing bump
steer. Removing one of the front shocks and bolting a laser (e.g. laser pointer, or spirit level with built in laser) to the hub seems to be a
popular way of doing this as it can be made very sensitive depending on how far you project the laser.
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muzchap
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| posted on 18/1/06 at 07:39 PM |
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Rusty Nuts
I said the 'FRONT' of the car is book chassis.
It's just the rear that's wider to accomodate the IRS set-up.
That's what I've been led to believe anyway... 
I don't claim to know conclusively, hell I'm just a basic amateur - was just trying to help the guy out with his positioning...
If you look at the luego mount - it's SLOTTED to allow continual adjustment - which is a very good idea
[Edited on 18/1/06 by muzchap]
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big_wasa
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| posted on 18/1/06 at 10:15 PM |
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Here is mine.
I followed Rortys advice. I fitted all the wishbones/uprights and rack, I tacked the front of the rack mount like a hinge and cycled it repeatedlie
moving the rack up and down a small bit at a time untill I got the least deflection (bump steer ) . The rack ended up about 6mm down the mounts
compared to the book and about 25mm lower at the back of the mounts more than the drawing in the book.
 
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JB
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| posted on 19/1/06 at 04:30 PM |
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Ackerman
quote:
Originally posted by britishtrident
Viewed from above the outer Track rods should be slightly ahead of the rack --- just look at a Sierra, Mk1/2 Escort, Capri, Avenger. The reason for
this is it the way cars with rack and pinnion steering get any ackerman angle ie. toe-out on turns.
Putting the rack head of the outer track rod ends will give toe-in on turns leading to poor turn in and very iffy handing.
[Edited on 18/1/06 by britishtrident]
I always thought that ackerman was determined by the position of the track rod ends in relation to the pivot point of the upright (ie a line drawn
through the lower and upper ball joint) The position of the rack forward or backward (so the track rods point either forward or backwards) determines
the rate of ackerman during turning.
My advise would be to have the trackrods perpendicular to the centre line of the vehicle and 100% ackerman.
100% ackerman is where a line drawn from the trackrod end, passing through the above mentioned pivot point of the upright coincides with the centre of
the rear axle. With a front rack this can be awkward to obtain due to the trackrod and disc getting close.
Carroll Smith has lots of thoughts on ackerman in his books and his ideas actually change with each book.
John
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MikeRJ
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| posted on 19/1/06 at 11:20 PM |
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quote:
Originally posted by JB
I always thought that ackerman was determined by the position of the track rod ends in relation to the pivot point of the upright (ie a line drawn
through the lower and upper ball joint)
That is true only for systems that have a tie rod directly between the two steering arms, e.g. anything that uses a steering box rather than a rack
and pinion. The ball joints on the ends of the tie rods rather spoil the ackerman geometry, positioning the rack so that the tie rods are at an angle
with the wheels straight ahead helps to counteract this.
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britishtrident
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| posted on 20/1/06 at 11:16 AM |
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Yes you only really get true "text book" ackerman on cars that have a centre track rod and idler arms with and old faishioned steering
box. As most of the motor mechanics text books are aimed at heavy goods vehicle mechanics it is still version that is taught.
A couple of the less techie kit car companies really haven't a clue about the importance of getting the steering rack position right worse they
haven't even he sense to copy the donor in this respect.
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britishtrident
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| posted on 20/1/06 at 11:18 AM |
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quote:
Originally posted by big_wasa
Here is mine.
I followed Rortys advice. I fitted all the wishbones/uprights and rack, I tacked the front of the rack mount like a hinge and cycled it repeatedlie
moving the rack up and down a small bit at a time untill I got the least deflection (bump steer ) . The rack ended up about 6mm down the mounts
compared to the book and about 25mm lower at the back of the mounts more than the drawing in the book.
What looks right is right --- and it looks pretty near perfect to me ;-)
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NS Dev
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| posted on 20/1/06 at 04:07 PM |
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Simple answer, Yep!!!
The advice to swing the wishbones up and down and clock the actual bump steer is the only way to know without drawing it all up.
Rack slightly behind the steering arm pivot ends is "about right".
JB's advice is also correct, the main influence on ackerman is the in-out positioning of the steering arm pivot point on the upright, which is
what I adjusted on my grasser to get sensible ackerman with a very short wheelbase. This also allowed me to move the pivot rearwards, shortening the
steering arm giving a quicker steering ratio as well.
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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