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Old 12-22-2008, 12:05 PM
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suspension geometry

hello all,
i'm planning a complete frame for my 1983 cadillac coupe deville and fabbing my own rear independent suspension and control arms, also fab the front independent front, as i've read in couple post the front should be 5 degrees for caster tilting a arm back 5 degrees, and have read to have control arm in the front tilted at a up ward angle for geometry, but no one has given a degree of this angle ?, i bought the book STREET RODDERS CHASSIS & SUSPENSION HAND BOOK, and was informational, but did'nt really give any degree angles for any kinda references, mostly talked about mustang 2 front ends as kits, knowing you need to have the a-arm in a up ward tilt so the geometry keeps camber with in the right geometry, and knowing no need for caster in the rear as they don't turn, mainly need a camber and a toe adjustment for rear suspension, so looking for some kinda base reference on settings of degrees for a base setting, or a book that maybe bought or anyone have a point of reference. as i've found a couple post with some diagrams. as i'm going to fab my own rear spindles and using bear hobs from a S/10 4X4 front and axles, and a 1982 -1992 camaro rear center cut it down and have axles custom made so can bolt S/10 inner CV joint to, been planning it in my head just as of yet, but planning doing a drawing soon of said rear suspension i have got in my mind,
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Old 12-22-2008, 07:10 PM
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Been there, done that.

What you need is Carroll Smith's book Tune to Win. By the time you get through absorbing Mr. Smith, you'll be able to construct what he calls "paper dolls" and roll the suspension through bump and droop to get everything sorted out.

I hunted and read everything I could get my hands on trying to figure out IFS. Nothing made any sense until I read Smith. Then it all just fell into place. Constructed an IFS that had zero bump steer through 9" of travel (4 1/2 in bump, 4 1/2 in droop) and made 3 degrees of camber gain at full bump with minimal scrub.
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Old 12-22-2008, 11:19 PM
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Designing and understanding the geomotry of a front end is a TALL task.

You could study for a year and not have the understanding it takes to pull off what goes into it.

Tilting the "a arm" back doesn't give you caster. Caster is the leaning of the "knuckle" or spindle back. The degree you lean it depends on what you are going to use the car for, and it depends on a number of other factors in the design as a whole.

The less caster as a rule, the more the wheel "bites" as it goes around a corner, thus, a degree or two would be more for a canyon carver. While the more positive caster gives you less rolling resistance. Five degrees is on the high side and more for a highway car. Big BMWs or Mercedes will have 5-7 for instance. A salt lakes car going for super high speeds will have something like 18 degrees positive caster!

The leaning IN of the pivot points on your knuckle or spindle is called "SAI" or Steering Axis Inclination, or "King pin Inclination" on a straight axle car.

The lean of the tire is called camber.

The tilting of the upper control arm is for "anti dive" (basically).

The shorter upper control arms give you the neg camber when the tire goes up as the car is leaning into it giving the tire more bite.

There is a TON to learn, why not just copy a KNOWN suspenson that will give you what you are after? A seventies Camaro is a good all around design that with a few tweeks and a few trick add ons can make for a super overall suspension.


Brian
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Old 12-23-2008, 01:19 AM
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holy cows, an intelligent question and what a bag of worms you are opening. CASTOR:

positive castor on a simple straight front axel car as an example (ifs works the same way) the car will raise and the tires will tilt away from the turn, as the car leans away from the turn the tires will again become 90 degrees to the pavement, thus max traction. the lifting of the front of the car as you turn the wheel is what causes the wheel to return to center if you let go of it after the turn. i run 8* positive on my straight axel gasser and can hold the wheel with 2 fingers and focus on the tach and the shift points. on my 2 road race cars i run 3-6* positive castor, it gives good road feel and still allows good centering of the steering. don't go anywhere near 0 or negetive castor, the car will be squirelly or uncrollable. as brian said, leaning the top of the spindle back increases pos castor.

ALSO, as brian pointed out, KPI (king pin inclanation, or the ball joint centerlines should intersect with the center of the tire at the pavement. this reduces scrub on the tires.

CAMBER:
this has to be factored in with castor and body lean in and out of corners. camber should always be 90 degrees to the pavement, but you also have to factor in tire distortion. i find that stiff shocks (KONIs set stiff) big sway bars and regular springs give me the most predictable and consistent results through high speed turns.

as far as toe, you should set the the the front toe at the front to 1/8 toe-in, anything close to 0 toe or toe-out will make the car once again squirrely.

as for your pics. the SLCAs (short-long control arms look pretty good) the mounting points may not be quite right. as far as brian's suggestion to look at a camero's suspention set-up, i would model mine off a C-4 corvette (sorry brian) the C-4s could do 1G (or close to it on the skid pad) i've read anything between .92 Gs and 1+Gs.

i could go on an on, but it's late. just be advised i am an old time alignment guy and know what i'm talking about.
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Old 12-23-2008, 09:55 AM
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i under stand alinement as i to have done front end alinements in many different alinement machines over the years, and yes be easier to use control arms from other cars, thought about corvette control arms and spindles, i'm a die hard GM guy and don't want any ford parts on my cars, and being a full size cadillac coupe deville also feel mustang 2 front not heavy enough for my cadillac, i know i maybe crazy for tricking out a large car like this but i like the car alot, and have 2 coupe devilles, a 1983 and a 1984, in 84 they only made 5,000 coupe devilles, so that one going keep close to stock, but the 83 planning to be my hot rod cadillac, the handling is slow on these cars, as to these cars are cruisers and not road handlers, as putting in a 472 with a fabbed intake using fuel injection as a 6 pack throttle body unit, but would like to have this car to go out looking for JUNKSTANGS, thank you for your info and input, yes i know alot geometry to deal with, with x-mas going on now can't find time sit down and draw out my design for the IRS & IFS suspension yet, so i'll be going to book store getting the book you have said about, i dig this site as i been getting alot input from many memebers on many projects, what steering rack would you say to use? as i guess would be alot to do with the width of my car, was thinking using a rack from a 1995 Z/34 monte carlo, with sport steering, i found a site where get about anything to fab a suspension www.welderseries.com there mostly for street rods but feel i can incorprate some these parts in my build. thank you again for your help!!!!. ASHES TO ASHES, DUST TO DUST, WAS NOT FOR FORDS MY TOOLS WOULD RUST!!!!!!
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Old 12-23-2008, 12:03 PM
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When I suggested going with a tried and true suspension I meant to COPY it not use the same parts, I'm sorry I didn't make that clear.

Brian
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Old 12-23-2008, 01:12 PM
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ok i was thinking that to and thank you for your input, very greatful!
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Old 12-23-2008, 04:13 PM
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Ralph, that link is solid gold buddy, thanks very much. It doesn't matter which rack you start with, but that is the key, to start with the rack and build the system around it. If you build the system to an arbitrary set of values and then try to match up a rack to it, you'll be pulling your hair out. I started an MII rack and then used Lincoln spindles with fabricated steering arms heliarced and gusseted to the front of the spindles. Why Lincoln? Because I had 'em and the brakes and ball joints were huge. I parted out a Mark V to get the front and rear suspension parts and 9 3/8" diff. I measured the length of a MII steering arm from the centerline of the ball joints to the center of the tie rod mounting hole on a friend's spindle. I made the fabricated steering arms with three tie rod mounting holes, the center one the same length as the stock MII, then one in front of that to slow down the steering and one to the rear of it to quicken the steering. I turned down bushings on the lathe and reamed them with a tapered reamer I bought from Speedway Motors (1 1/2" per ft. taper). Hole-sawed the arms, dropped the bushings in and welded them.

Your project probably won't have anything in common with the one I did, but I'm just throwing out some of the things I did in order to get your juices flowing.

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Old 12-23-2008, 06:01 PM
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472 Fuel Injection

A little off topic; What are you going to use for the fuel injection setup? I have a '67 Deville convertible that's receiving a '70 eldorado 500, and want to use FI. I've read about using a Ford 460 fuel injection system on the Caddi engine, and mid-seventies Eldorado FI. I even looked into Mega Squirt. What ideas do you have?
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Old 12-23-2008, 08:42 PM
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Quote:
Originally Posted by cacsmret
A little off topic; What are you going to use for the fuel injection setup? I have a '67 Deville convertible that's receiving a '70 eldorado 500, and want to use FI. I've read about using a Ford 460 fuel injection system on the Caddi engine, and mid-seventies Eldorado FI. I even looked into Mega Squirt. What ideas do you have?
Never thought about using 460 EFI on a 500, but it sounds viable. Price makes the adapter plates to put the 460 manifold on properly....
http://www.pricemotorsport.com/html/...apter_kit.html
and I would think a guy could rescue the 460 EFI intake and all the associated computer and other electronics from a boneyard.

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Old 12-24-2008, 12:53 PM
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as to my fuel injection set up, well going make the whole intake either out aluminum or stainless steel, and three throttle bodies from 4.5 cadillac the
HT-4500 motor, and yes use the mega squirt EFI and also the cadillac 4.1 EFI system, going to be a procressive system what i'm try to do, going run on the 4.1 EFI for just curising around, and have the mega squirt to come in later using a secound TPS sensor on the rear throttle body, but the center throttle body will have the stock injector bod with 454 injectors in the bod, so it will run on the center throttle body till you open the throttle, and than the multi port system kicks in, use cadillac dist. for a 425 HEI comptuter controled, or 368, and all the sensors, fabbed headers, and the mutli injector from a 4.5 cadillac, hopefully plan will come togethere!
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Old 12-24-2008, 01:27 PM
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You guys doing the big cads need to get to know the cad 500 guy in New mexico..he has the manifold base plate for building a custom intake as well as the head parts and pieces for the valve train..He goes 10.50 in a full size cad seville so he gets the results..he has the header flanges as well..great resource..if I were to go EFI on a 472/500 I would go with megasquirt myself but I do have some support for that sort of thing from the guys at the landspeed shop..

Sourcing of books and software on suspension I use Steve Smith Autosports for that as they have a lot of titles..mostly circle track but those guys do a lot with these suspensions and the lessons do apply..

Sam
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Old 12-25-2008, 06:04 AM
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yes i have his site, also my nephew machinest and has a water jet and laser machine to cut out most anything i need, and i also like making most my own stuff, part of hot rodding!, also been to 4 book stores now no one has the carroll smith's book, guess order it on line, hey thanks everyone, for all the input!!,
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Old 12-25-2008, 11:19 AM
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i'm sorry i put link to the welding site did'nt know! seen links in other post! so i'll not do it again! just seen other people asking questions and was trying help out with there builds, so very sorry hot rodder forum!!!
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Old 12-25-2008, 12:23 PM
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Quote:
Originally Posted by rachet ralph
i'm sorry i put link to the welding site did'nt know! seen links in other post! so i'll not do it again! just seen other people asking questions and was trying help out with there builds, so very sorry hot rodder forum!!!
Not to concern you too much..if one links to another forum such as this that provides tech info that works..we can tell usually if the site linked to is for personal gain..

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