stuleah
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| posted on 15/8/08 at 08:21 PM |
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help with steering rack please.
how impotant is it to get the ball joints/pivot points on the steering rack in line with the pivot point of the wishbones.
would it matter if they sat in a bit (so the rack in theory is too short), as i have an escort rack and i am not sure if it will now do the job.
thanks in advance for anyy help.
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nitram38
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| posted on 15/8/08 at 08:34 PM |
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If you draw a line from your top wishbone inboard mounts through to your bottom inboard mounts, your rack ball joint centre MUST be somewhere along
this line, unless you want bump steer. (un-equal A wishbone setup)
I don't know your set up, but sometimes raising or lowering the rack can make the ball joints line up, but then your track rod ends might be at
an angle which becomes another problem.................
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stuleah
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| posted on 15/8/08 at 09:22 PM |
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the top and bottom wishbone mounts are vertical, so there is no angle between the two. got me wandering now does it matter if the wishbones are
mounted in this way. done as much research as possible but it kinda gets confusing after a while.
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nitram38
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| posted on 15/8/08 at 09:27 PM |
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It is very unusual to have them directly in line with each other!
What you describe is equal length wishbones which will travel in parrallel so in body roll will give unpredictable handling.
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stuleah
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| posted on 15/8/08 at 09:41 PM |
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if i move the bottom one in so that it is unequal, is there a correct amount of angle to aim for from the top to bottom or is it as imple as added
1" or so to the length of the bottom bone?
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nitram38
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| posted on 15/8/08 at 09:53 PM |
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It is not that simple 
Guessing the distance may give you a bigger headache.
I had to determine how much camber gain/loss I needed over my wheel travel first before determining my pick up points.
The wishbone mounts may also have to be raised or lowered to give you the optimum camber change you require.
The easiest way is to make 2d (end on )models and use pins to move your mounts about and even lengthen/shorten your bones.
They may not be parrallel with each other with one bone at an angle.
These are my solidworks models but bear in mind that my suspension is for ride height adjustments over a 6" range. (air shocks with
compressor)
Yours might only be a few inches of ride height change.
 
Description
 
up
[img][/img]
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stuleah
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| posted on 15/8/08 at 10:01 PM |
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why is nothing ever simple???
i will give the 2d idea a try.
looking at your diagrams that explains what i have to do, thanks.
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nitram38
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| posted on 15/8/08 at 10:13 PM |
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This might help too:
 
unequal wishbones
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britishtrident
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| posted on 16/8/08 at 07:25 AM |
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With Cortina uprights ideally the distance between the steering rack inner ball joints should be slighly wider (say 0.5" to 0.75" than the
width between the lines joining the inner wishbone pivots --- this is because of the small ammount of ackerman built into the steering arms on the
upright.
The conventional layout for a light front engined sports car is to have the top wishbone roughly 2/3 to 3/4 the length of the lower
wishbone.
Normally the front roll centre should be located somewhere between 1" and 5" from the ground.
To achieve this the upper wisbone normally slopes upwards from the chassis to the wheel.
On the lower wishbone it is generally best if the wishbone pivot is about 0.5" above the the lower ball joint centre line when the car is as it
will normally be driven -- ie with driver or with driver + passenger.
The Lotus 33 front suspension in the picture shows the sort of proportions to aim for -- also have a look at Caterham/Lotus 7 front suspension.
[Edited on 16/8/08 by britishtrident]
 
Rescued attachment image0.jpg
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britishtrident
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| posted on 16/8/08 at 07:34 AM |
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quote:
Originally posted by stuleah
how impotant is it to get the ball joints/pivot points on the steering rack in line with the pivot point of the wishbones.
Actually this is wrong for most uprights ---
Most uprights have some ackerman offset built into the steering arms.
If the track rods are in front of the axle centre line then the steering rack ball ends should be slightly wider than the line join ing the inner
pivots of the wishbones.
If the track rods are behind the axle centre line then the steering rack ball ends should be slightly narrower than the line joining the inner pivots
of the wishbones.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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stuleah
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| posted on 16/8/08 at 03:25 PM |
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thanks, the diagram helps.
thanks for the info britishtrident that helps alot aswell.
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