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Old 02-03-2006, 03:01 AM
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Correct IFS setup?

After studied a number of independent suspension kits, it's something i don't understand.

All of the well known manufacturers agree that moving the upper A-arm bolts down (to clear front fenders) is not good. The explanation is that Ford did their homework on that suspension and both upper and lower A-arms should be parallell to each other and with the ground when seen from a front view.

But have a look at this drawing from one of the manufacturers catalog:


According to this, the A-arms should NOT be parallell to each other, and the lower A-arm should not be 100% parallell to the ground either.

What important point have I missed here?

Not that it bothers me. Im building a 34 highboy, so my IFS kit have plenty of room. It just that I like to understand things.

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Old 02-03-2006, 04:03 AM
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theres alot of tech that goes into building a proper IFS, and changing one item is like building a house and making one wall on the first floor 4 feet instead of normal height .... it just doesnt work out right ...

heres some of the considerations ..

angle of the balljoints in relation to each other
length of the control arms
placement of the tierod
length of the tierod
angle of the tierod
caster
antidive angle
scrub raduis

the list goes on

if anyones going to build their own front suspension ... copy something EXACTLY ... such as a corvette IFS

theres nothing like finding out that your home made suspension locks up when you are making a panic stop while trying to swerve out of the path of something (garbage can, car, small child)

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Old 02-03-2006, 05:50 AM
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Perhaps the suppliers are concerned about a possible liability problem. Since parallel lines meet at infinity, the situation which they're recommending would put the roll center at ground level, which, while not minimizing roll, is "safe." The real danger, with an IFS, is a roll center so high that "jacking" occurs. This is when, during hard cornering, the outside tire suddenly tucks in, the car is "jacked up," the CG height is increased, and, in the most severe cases, rollover occurs.

By giving you setup instructions which ensure that the roll center is at ground level, they know they're not going to be involved in expensive litigation.
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Old 02-03-2006, 10:59 AM
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Quote:
Originally Posted by staleg
All of the well known manufacturers agree that moving the upper A-arm bolts down (to clear front fenders) is not good. The explanation is that Ford did their homework on that suspension and both upper and lower A-arms should be parallell to each other and with the ground when seen from a front view.

But have a look at this drawing from one of the manufacturers catalog:


According to this, the A-arms should NOT be parallell to each other, and the lower A-arm should not be 100% parallell to the ground either.

What important point have I missed here?

Not that it bothers me. Im building a 34 highboy, so my IFS kit have plenty of room. It just that I like to understand things.
What you are missing is the design specs for the other manufacturer. IF they redesigned all of the geometry points to work in the orientation pictured, their suspension should work just fine. The MII suspension that everyone has copied is designed to work one way... as Ford designed it... When you start hap-hazzardly moving points around (like the upper A Arm pivots you described) this will affect the way the entire suspension works and, if you don't redesign the other points to work with the "new" points, it will not handle well.
Like was mentioned above ALL of the points are interactive. When you move a few, without redesigning the entire suspension, you upset the relationships and the suspension becomes junk...
Be careful of what you buy. many of these aftermarket kits ARE junk...
Mark
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Old 02-03-2006, 01:04 PM
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I've already bought a Fat Man Mustang II "Stage III" kit with pro shock coilover towers.

Guite a few guys on this board don't like Fat Man Fabrication too much, I've seen.
I will not jugde my kit as crap just because of that. but It's good learning for me too hear critical voices in advantige too.

I have posted this in another discussion board, too. Always good to hear several opinions.

The answers on the spescific drawing and my questions around it are somthing like this:
First: A correct Mustang II setup do have a smaller distance between the upper and lower control arm mounting bolts than between the upper and lower spindle ball joints. I thought the upper and lower A-arms were parallell, and I was wrong.
Second: The drawing does not nessaccarily show actual ride high. It just shows how the different mounting points are related to each other. If the car is slightly lowered so the lower A-arms are equal does not destroy the principles.

Not that any of the answers here in this thread are wrong, of course!
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