I dont know if this will work, but an interesting tech article on M2 design and layout.....Independent suspension can be very simple and very complicated at the same time. Success in making it simple is learning the rules. And it has it's own set of rules. Important, Rule #1: Unlearn everything (almost) you know about steering and suspending a car with a solid axle and 4-link suspension. That would be like trying to play football using baseball rules.
The first thing to relearn is the action of the front axle and spindle during suspension travel. There are three things to control in the front wheel: camber, caster and toe angle.
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CAMBER AND CASTER
In a solid axle the camber is built into the axle and the caster built into the 4-bar design. Both are constant (they don't change during suspension travel). A solid axle moves basically straight up and down therefore, so does the spindle.
On an IFS System, the upper and lower control arms, as well as the spindle and car chassis, form an uneven parallelogram, as viewed from the front (see Fig. 1 & 2). The spindle moves up and down in an arc or radius, which is determined by the length and placement of the two control arms. Their placement also determines the amount of caster and camber change.
Fig. 1 -- Click for larger image
This is a correct Mustang II front suspension in a street rod, when the stock Mustang II suspension locations are used. Notice the parallel upper and lower arms. Also notice there is minimal camber change and almost flat radius (1) in the movement of the spindle during suspension travel.
Fig. 2 -- Click for larger image
Now we have added the stock Mustang II steering rack in the stock Mustang II location using the stock Mustang II tie rod ends. Notice the radius of the rod ends (2) matches the radius of the spindle. Also, more importantly, see that the inner tie rod pivot (3) is IN LINE with the inner pivots (4) & (5) of the upper and lower arms. This is absolutely necessary. Ford Motor Co. did their homework.
Important Rule #2: If any of the four pivot points are moved in any direction, for any reason, the spindle swings in a new, unique arc which is different from the old radius. Usually the inner pivot point of the upper arm on the Mustang suspension is the one to be moved. The control arm is usually shortened and the pivot shaft lowered to clear fenders on some cars (see Fig. 3). As you can see, the spindle will now swing in a new higher radius. That in itself is not a problem. But, please read on, as it is about to get real interesting.
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TOE ANGLE
The paragraphs that follow explain why Heidt's Hot Rod Shop does not make Mustang Kits for certain cars.
As we mentioned, there are three things to control in the front wheel. Camber and caster we've already covered. The third is the toe, or steering angle at which the wheel is pointed, which determines where your car goes.
You can see that this means the spindle must always remain in the direction you have pointed no matter where the spindle is in the suspension travel. This is the job of the "Tie Rod". As you can see, the exact length and location of the inner pivot of the tie rod must be very carefully selected so the outer ends of the rod, which is attached to the spindle, swing in a radius which matches the spindle radius exactly. When deigning a brand new suspension system on the drawing board this determination is very easy to make, since the tie rods on the rack are actually designed to match the control arm and spindle radius. But on your conversion, this is where the problems start. So this is the next thing to unlearn.
When mounting a steering box in a solid axle installation, motor mounts, etc. usually dictate the location of the box and the pitman arm is modified to align the drag link with the tie rod. Selecting and installing a rack-and-pinion is nowhere near that simple or forgiving. When adapting an existing suspension design, such as the Mustang design, it is very important to keep every single mounting location and pivot point, including the rack, in their original designed places. As you have just seen, the Mustang rack, with a specific tie rod length, was designed by Ford to match the swing radius of the Mustang spindle using stock length Mustang control arms in the locations which were selected when the Mustang was originally designed.
Fig. 3 -- Click for larger image
This is a typical "modified" Mustang II installation in a '32 Ford type car. This first change is to shorten and drop the upper arm pivot (4) to clear the fender. This causes the much sharper radius (1) of the spindle and resulting increased camber change. Also notice that the two arms now intersect at a theoretical point (9). But this alone is not the bad part. The next step will show you why.
If you shorten or lower the inner pivot point of the upper arm, the spindle will now swing in a new, different radius which no longer matches the current tie rod radius. If you raise or lower the rack location, or change the tie rod length for any reason by using a longer tie rod end, the tie rod will swing in a new radius which does not match the current swing radius of the spindle (see Fig. 4).
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EXPLAINING BUMPSTEER
The bottom line of all this radius explanation stuff is this: Since the tie rod ends attached to the spindle steering arm, the tie rod controls the steering angle of the front wheels. If your car goes over a "bump" the spindle goes up and down in its swing radius, determined by the upper and lower arms (remember?). If the tie rod swings in a different radius than the spindle during this suspension travel it will push or pull on the steering arm of the spindle, changing the direction of the front wheel, "steering" the car. And that is how the term and the monster "BUMPSTEER" were created, where 95% of the problems with incorrect suspension design are found. It is from people not really understanding this most important relationship between the tie rod length (not the overall rack length) and the spindle swing radius. They feel that if they are able somehow with enough modifications to the parts to "physically assemble all the parts" that it must be OK. Then they pull down the driveway, over that first curb and low and behold: BUMPSTEER. When you drive a car with BUMPSTEER, the car tends to wander and hop around as you drive down the road over bumps and dips. You have to constantly steer the car to keep it in the lane. Not what you would call an enjoyable ride.
Fig. 4 -- Click for larger image
...it's all over by now. The other common modification/mistake is to widen the crossmember and use a long tie rod end. Ugh, as you can see, by adding the longer (incorrect) tie rod end, the inner pivot of the tie rod (3) now has been shifted way out of line by the dimension (6). Disaster! The flatter radius of the outer tie rod end (2) no longer matches the sharper spindle steering arm radius (7). This causes the spindle steering arm to follow the incorrect radius (2) and change steering angle, or "steer" as the suspension travels up and down over "bumps": more commonly known as "Bumpsteer". You can also see that the projected line from the tie rod does not intersect the intersection point (9) of the control arms. It should. This is why the only way the Mustang II system works correctly is the way Ford designed it, using all stock Mustang II parts, in the stock Mustang II locations.
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BUILT-IN ANTI-DIVE
Anti-dive is another characteristic required in an independent front suspension system. Anti-dive helps prevent the car from "nose diving" under hard braking conditions, hence the name. It is something which is found in every factory car manufactured, including the Mustang and Pinto, visible in the suspension design in the upper control arm. It is mounted on an angle, with the FRONT pivot higher than the rear, not level (see Fig. 5).
The actual description of how anti-dive works involves extensive vector force diagrams and is much to lengthy to describe here. Let's just trust the big three auto manufacturers on this one, because they all use it. The Pinto uses a 3° angle for their anti-dive in the upper arm. It may look funny only because you are not used to seeing it in a street rod. Look at your family car. Do things look more normal now?
Don't bother looking for it one somebody else's street rod, especially one with other Mustang kits on it. They don't always know why the upper arms are "crooked" and fix(?) them. But how funny would your car look with the bottom of the grille ground away from bumping the street?
Now for the real point of this whole technical explanation.
Fig. 5 - Click for larger image
This is the side view of a correct Mustang IFS kit. Not the angle of the upper control arm, that is higher than the front. This angle, through a lot of geometric forces in the spindle when braking, generates a lifting force on the frame at the inner A-arm mounts. This is the same angle as the Pinto, which gives the same amount of anti-dive force as the Pinto. Simply put, factory designs work the way they are supposed to in every respect, so why throw all their engineering and testing out the window?
This is the only way to incorporate this important feature, no matter what else you have heard. If you cannot see the angle in the upper arm, then the anti-dive is simply not there. Period.
Bahhh.. the pictures didn't paste! For a full view go to
www.heidts.com and scroll to "other info", than 'tech info'...
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