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  #16 (permalink)  
Old 11-25-2013, 07:49 PM
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Quote:
Originally Posted by enjenjo View Post
It will change the Ackerman
It will also change the instant center.

If you have any interest in learning about IFS, read the book Tune to Win, by Carroll Smith. He was the crew chief for Ford Motor Co. when they went to Lemans and kicked Ferrari's behind with the GT40. In the back of the book, he explains how to make "paper dolls" by using paper and stick pins to mock up a suspension system and see how it works before commiting to hard parts.

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  #17 (permalink)  
Old 11-25-2013, 07:55 PM
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by the time you get it narrow enough you will have no turning radius . if you have to look for a mustang 2 or pinto and use the cross member.
the lower a arm pivot and the pivot of the rack must be the same or your going to get bump steer .
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Old 11-25-2013, 09:52 PM
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Hello Shine. If you have time I would really appreciate a more complete explanation of your last post. This is all new to me and I can use all the help you could offer.
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Old 11-26-2013, 12:40 AM
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If you narrow the crossmember, you have to narrow the steering linkage the same amount. That much you know. You cannot narrow the steering outboard of the inner tie-rod on the rack. Doing as you suggested in shortening the tie rods will introduce bumpsteer into the geometry. The rack unit itself has to be narrowed. That is where this all gets tricky and most likely kills any cost savings from using the Crown Vic front end. Best to go with a narrower front suspension.

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Andy
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Old 11-26-2013, 07:16 AM
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the problem with the crown vic is not the cross member but rather the length of the a-arms. by narrowing the cross member you are pulling the tires even closer to the frame. which will cut down turning radius . with the offset of the wheels it is even worse. running a skinny wheel will only help so much and the cost of them is going to be high. i just dont think the crown vic is a good choice for early cars. it barely works for the latter ford trucks. look for a mll . they are still out there .
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Old 11-26-2013, 08:38 AM
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Tech inspector is right about the roll center changing, it will get higher. Shortening a power rack is real complicated, you would be better off finding a shorter rack you can adapt. You might look at a Fox Mustang if you decide to go that way, it's about 6" shorter.

If you decide to go the mustang II route, Welders Series sells a Uweld crossmember that is self jigging for about the same price it costs me for the steel to fab one myself.
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Old 11-26-2013, 05:32 PM
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Quote:
Originally Posted by techinspector1 View Post
When you narrow the crossmember on a front clip, you toss away all the factory engineering geometry and end up with whatever you end up with.
not really, as you didn't change anything in the geometry, other than shorted the inner tie rods on the rack..
does the geometry change if I put a mustang II set up on a 35" wide rails, or a 32" rails, ? nope as the a arms/spindle etc didn't change nor did anything else other than shorter tie rods..
if I slice 4" out of the center of the c/v crossmember I haven't changed anything other than it's track width..
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Old 11-27-2013, 10:55 AM
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I thank everyone for responding. I have a question regarding the turning radius issue. Is this because the A arms are too short and move the tire too close to the frame? If so wouldn't this be helped by using wheels with more normal offset? As far as changing the inner tie rod ends goes, several of my daily driver Honda's have racks that are nearly identical and inner ends that are different lengths. Moog makes what they call "universal" inner ends. I don't understand the point of making other than original equipment parts if using these ends would cause steering issues. Is their a formula for the correct length of inner end that correlates to the width of the rack body? The "welders series" cross members look very good but that is such a small part of what you need.
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Old 11-27-2013, 11:23 AM
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your starting with 67 1/2 in track. by the time to hack this thing up your going to be well inside the frame rails which is going to create numerous problems with exhaust , steering etc . you would be better off leaving the axle under it. but it's your call .
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Old 11-27-2013, 11:27 AM
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Narrowing the crossmember and the rack will not in itself affect the turning radius. Clearance must of course be provided for the wheel/tire combo to reach the steering stops without contacting the frame. Changing the offset and size of the tire/wheel combo can provide this clearance as would narrowing the frame if necessary. Most likely though, a proper fitting wheel/tire package would be all that you need for proper clearance.

One point you seem to be missing though, is that you cannot make up the difference in the tie rods for the narrowing of the crossmember. The steering rack itself has to be narrowed, or use a narrower rack.

The best option is to locate a standard production steering rack that is narrower than the original by the amount you want to narrow the crossmember. Example-say you want to narrow the front suspension about 5 inches, go to the wrecking yard and find a rack that is 5" +/- narrower than your original (make sure that both racks have the pinion gear on the same side of the rack, either above or below) and purchase it. Then narrow your crossmember EXACTLY the amount of the difference in length between your new and old rack (measured to the pivot point of the inner tie rod end). Install mounts for the new rack on your modified crossmember. Make certain the height of the new rack relative to the crossmember is the same as the original. Once that has been completed, make up tie rods to connect the new rack to the stock outer tie rod ends. This last step may require some custom machine work or creative matching of OEM parts. Connect up your steering linkage and P/S lines and you will be good to go.

This is a great project and doesn't have to be expensive if you do some creative parts sourcing.

As a final note: Narrowing the front suspension will effect the Ackerman, but if the wheelbase of your project is shorter than the Crown Vic, the Ackerman may very well be correct for your chassis. If it is off a bit you won't notice it except maybe while driving around a gravel parking lot. Generally Ackerman is said to be right when the intersecting lines from the steering linkage meet at the center of the rear axle, but some designers locate that point forward or rearward of the axle for different reasons. I wouldn't worry about it.

Regards,

Andy
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Old 11-27-2013, 11:38 AM
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there is a huge amount of this crossmember outside of the frame. it barely works on f100 trucks. your going to be taking 10 inches or so out of it .
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  #27 (permalink)  
Old 11-27-2013, 11:48 AM
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Quote:
Originally Posted by gearheadslife View Post
not really, as you didn't change anything in the geometry, other than shorted the inner tie rods on the rack..
does the geometry change if I put a mustang II set up on a 35" wide rails, or a 32" rails, ? nope as the a arms/spindle etc didn't change nor did anything else other than shorter tie rods..
if I slice 4" out of the center of the c/v crossmember I haven't changed anything other than it's track width..
You need to do some reading, because it's clear that you don't know what you're talking about.....
Tune to Win: The art and science of race car development and tuning: Carroll Smith: 9780879380717: Amazon.com: Books Tune to Win: The art and science of race car development and tuning: Carroll Smith: 9780879380717: Amazon.com: Books
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Old 06-08-2017, 04:53 PM
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51 Dodge Wayfarer, Crown Vic front suspension

Hey Terry I was reading your post about the Crown Vic front suspension. I know it has been awhile since you posted if you could email me, [email protected] I have some questions you might have answers for. Thanks, Greg
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  #29 (permalink)  
Old 06-09-2017, 09:21 AM
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Quote:
Originally Posted by gergsggib View Post
Hey Terry I was reading your post about the Crown Vic front suspension. I know it has been awhile since you posted if you could email me, [email protected] I have some questions you might have answers for. Thanks, Greg
Click on his avatar and you'll see: "Last Activity: 10-04-2014 07:48 PM"

Russ
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  #30 (permalink)  
Old 06-10-2017, 11:35 AM
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When you mount a rack in any car, the inner pivots of the rack should be even with the inner pivots of the lower arms. That is so when it bounces the arms and tie rods bounce at the same angle. The tie rods must also be parallel with the arms or you will get bump steer -- when one wheel "bumps" up and down, that wheel will want to steer because the tie rod and lower arm don't move in the same arcs. So the rack width from pivot to pivot (inner tie rod ends... usually made onto the rack tie rods) has to be very close to the same as the distance between the lower arm pivots. If the rack is lower or higher the outer tie rod ends can be made lower or higher using spacers -- might need different outer tie rod ends though. If you have just a little bump steer you will probably not notice. I think the rack on my 63 Rambler (custom install, obviously) is about 1/4" higher than the lower arm pivots. I get a little pull on the steering wheel when one tire hits a bump, but not enough to be of any concern. Been driving it since 2003 that way.

Same with Ackerman. I computed what the Ackerman angle should be for my car, then looked at the alignment specs in a factory manual. Ackerman was off by 3-6 degrees! Obviously it doesn't have to be perfect, but the more off it is the more tire scrubbing you will have. Radials are a lot more forgiving! I can tell I'm getting a little scrub, but mostly when backing and turning sharp.
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