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PostPosted: Tue Jan 30, 2007 2:03 am 
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I am going to fabricate control arms for my Mustang II uprights. I dont have a set to jig and copy, but i was wondering if someone with a set could share some dimensional information.

Image

the plan is to use .156 wall 1" dom which will allow me to use 3/4 rod ends. because I am using coilovers instead of coil springs they dont have to be so fargin wide. So the width or angles on the arms is of no concern, I am more or less concerned with the upper and lower ball joint angle as well as the centerline distances from the ball joint to the centerline of the arms bolt points. I guess the dimesnions of d and e dont really matter but A, B, C, and the angle of X (if any) are important.

any info here would be much appreciated.


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PostPosted: Wed Jan 31, 2007 12:21 pm 
Okay - I'll give you what I've got for my Mustang II spindle setup. For the LOWER A-arm, Dimension E = 10 3/8", dimension D = 8", dimension B & C are the same at 1/2 of E (so, 5 3/16"), A = 12 1/2", and angle X = 0 degrees (there is no need to angle this on the lower A-arm, as the ball joint will accomodate a much larger angle than the kingpin inclination will generate). For the UPPER A-arm, E = 10 3/4", D = 8", again B & C are equal, A = 10 3/8", and angle X = 10 degrees (approx.). Here again, the angle is not critical, as the ball joint (I used Monoball joints) will accomodate quite a bit of angle on its own.

Bear in mind that you may have to change the length of the arms, depending on the width of your frame (mine is a book nose width) and the width of your rear axle, so the front track of the car is roughly the same as the rear track. There are some photos of my front suspension on my website for your perusal. Hope this helps...


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PostPosted: Wed Jan 31, 2007 12:28 pm 
Oh, and I should have mentioned that IMHO you should make the sides of the A-arms the same length, and make the upper a-arm assembly able to be adjusted fore-and-aft to adjust for castor angle. If you try to achieve castor by making the B & C dimensions different, you'll be stuck with whatever castor angle this results in, and you really won't know what this should be until the car's tested on the road. If it's welded-in castor, and it turns out to be wrong, you're kind of stuck. If you build longitudinal adjustability into the upper arms, you can dial in whatever castor angle you like. Mine are adjustable fore-and-aft for castor, up and down for camber, and they can be angled for anti-dive.


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PostPosted: Thu Feb 01, 2007 3:32 pm 
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thanks for all the info. What are your thoughts in terms of coilover angle and mounting position on the lower arm in terms of mounting distance from spindle?


the first pic was to get dims off the typical aftermarket style a arms.
but the ones I am making will use heim rod ends. what I imagine is standard is to find center point of the thread on the rod ends and use that position to set your final dimensions off of to give you even adjusability in and out.

Image
Image


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PostPosted: Thu Feb 01, 2007 3:54 pm 
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Location: Charleston, WV
T0M wrote:
thanks for all the info. What are your thoughts in terms of coilover angle and mounting position on the lower arm in terms of mounting distance from spindle?


the first pic was to get dims off the typical aftermarket style a arms.
but the ones I am making will use heim rod ends. what I imagine is standard is to find center point of the thread on the rod ends and use that position to set your final dimensions off of to give you even adjusability in and out.

Image
Image


The further inboard from the balljoint that you mount your coilover, the greater the pressure exerted on the control arm. You should try and get it as close to the balljoint as possible. Regarding the angle, the steeper the angle the more spring rate you need because the spring looses efficiency (if that's the right word.) the more that it is tilted. There are several calculators out there on the internet that will help you select a spring once you know your angle and your desired wheel rate.

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PostPosted: Thu Feb 01, 2007 11:29 pm 
I agree with chetcpo - keep the lower shock mount well out on the lower a-arm, and brace the hell out of it with welding (take a look on my website for pics of mine). Remember, the upper a-arm just locates the front end, but the lower a-arms take all the loading from the shocks/springs, impacts, most of the steering loads & braking loads, etc. In order to keep my shocks from laying down too much (consider that when your shocks are laid down some, the springs become "falling-rate", because they start to approach being horizontal as they compress), I made a frame brace/extension that kicks the tops of the shocks outboard. That allows my shocks to still be fairly vertical, while being fairly far out on the lower a-arms (again, pics on my website). As an added bonus, it means my big chrome 7" headlights have a nice place to mount... :D :D


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PostPosted: Thu Feb 08, 2007 12:54 pm 
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I just read in a recent post here that theres a tie rod style ball joint (moog es150r) that fits the pinto taper.

this would allow for a different type of control arm.
Image


which would be a better design ? having fixed screw in ball joints and adjustable heim rod ends for the pick up points, or having adjustable tie rod ball joints and fixed pick up points?


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PostPosted: Thu Feb 08, 2007 2:00 pm 
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I think the adjustable pickup points allow more alignment options. You can change caster as well as camber with those. My question is why not use adjustable pieces on all three corners of the CA? :P

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PostPosted: Sun Feb 11, 2007 2:29 am 
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zetec7 wrote:
Oh, and I should have mentioned that IMHO you should make the sides of the A-arms the same length, and make the upper a-arm assembly able to be adjusted fore-and-aft to adjust for castor angle. If you try to achieve castor by making the B & C dimensions different, you'll be stuck with whatever castor angle this results in, and you really won't know what this should be until the car's tested on the road. If it's welded-in castor, and it turns out to be wrong, you're kind of stuck. If you build longitudinal adjustability into the upper arms, you can dial in whatever castor angle you like. Mine are adjustable fore-and-aft for castor, up and down for camber, and they can be angled for anti-dive.


so how would I design the top to properly adjust castor? Lets say I am going to use the tie rod on the upper and the screw in ball joint on the lower using the tie rod to set the camber and the heim ends to set the castor.

would the rod ends being parallel(like in the top pic) still be able to create enough offset to change the castor by pulling in one end and pushing out the other or would I be better off angling the rod ends outwards(like in the bottom pic)) to give me more castor adjustment?
Image
Image


Last edited by T0M on Sun Feb 11, 2007 2:33 am, edited 1 time in total.

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PostPosted: Sun Feb 11, 2007 2:33 am 
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chetcpo wrote:
I think the adjustable pickup points allow more alignment options. You can change caster as well as camber with those. My question is why not use adjustable pieces on all three corners of the CA? :P
im starting to think thats best. :ack:


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PostPosted: Sun Feb 11, 2007 8:35 am 
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Comparing sphericals to bushings is like comparing apples to oranges. There are too many variables, such as add-on rubber seals, types of races, and materials. To have a fair comparison, I will compare based on a bushing that costs near the same price as a spherical.

Sphericals do not last as long as bushings because loading is concentrated in a smaller area and dirt more easily penetrates the joint. More vibration is transmitted with sphericals depending on the durometer of the bushing. Sphericals require spacers between the frame mounting ears for clearance.

Sphericals are not required on the frame pivot end of lcas and ucas unless the frame designer has created the need (i.e. to replace a strut rod). As long as the bushing length is not long enough to cause binding, cam bolts installed on the lcas can be used for adjustment of caster & camber (i.e. stock miata). A spherical used in the above designs requires dissasembly for adjustment.

Sphericals or "johnny joints" should be used with a non-independant axle instead of bushings. When one wheel goes over a bump, the axle needs to be able to twist in its mounts. The rock crawlers call this "articulation". The idea is to minimize bind to allow the dampers and springs to do their thing while reducing the stress in the frame mounts.

An oem tie rod is a better choice for the upper balljoint replacement than a spherical because it is designed for a dirty environment, is often offset to allow its use where a standard spherical would need to be a special type to prevent binding, and is lubeable. Lubing cleans the tie rod of any contaminated grease, water, and dirt that may have entered the joint. Sphericals dont need lubing but they dont displace water and to use a aerosol to remove the dirt would probably remove the lubrication.

The tie rods taper provides a much greater contact area than a straight bore. The internal race has a much greater contact area than the typical spherical used to replace it.

IMHO, a street driven vehicle should have bushings and oem type joints where practical. A fair weather hot rod or race car should have sphericals. Do what you want. It will be cool either way.

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PostPosted: Sun Feb 11, 2007 6:38 pm 
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Miatav8,MstrASE,A&P,F wrote:
Comparing sphericals to bushings is like comparing apples to oranges. There are too many variables, such as add-on rubber seals, types of races, and materials. To have a fair comparison, I will compare based on a bushing that costs near the same price as a spherical.

Sphericals do not last as long as bushings because loading is concentrated in a smaller area and dirt more easily penetrates the joint. More vibration is transmitted with sphericals depending on the durometer of the bushing. Sphericals require spacers between the frame mounting ears for clearance.

Sphericals are not required on the frame pivot end of lcas and ucas unless the frame designer has created the need (i.e. to replace a strut rod). As long as the bushing length is not long enough to cause binding, cam bolts installed on the lcas can be used for adjustment of caster & camber (i.e. stock miata). A spherical used in the above designs requires dissasembly for adjustment.

Sphericals or "johnny joints" should be used with a non-independant axle instead of bushings. When one wheel goes over a bump, the axle needs to be able to twist in its mounts. The rock crawlers call this "articulation". The idea is to minimize bind to allow the dampers and springs to do their thing while reducing the stress in the frame mounts.

An oem tie rod is a better choice for the upper balljoint replacement than a spherical because it is designed for a dirty environment, is often offset to allow its use where a standard spherical would need to be a special type to prevent binding, and is lubeable. Lubing cleans the tie rod of any contaminated grease, water, and dirt that may have entered the joint. Sphericals dont need lubing but they dont displace water and to use a aerosol to remove the dirt would probably remove the lubrication.

The tie rods taper provides a much greater contact area than a straight bore. The internal race has a much greater contact area than the typical spherical used to replace it.

IMHO, a street driven vehicle should have bushings and oem type joints where practical. A fair weather hot rod or race car should have sphericals. Do what you want. It will be cool either way.

i just wanna make sure my castor is correct and I dont get bump steer :)


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PostPosted: Sun Feb 11, 2007 8:02 pm 
There's no way I know of to calculate the required castor angle - basically, if you make it adjustable (by engineering some way to move the upper a-arm fore-and-aft), and you leave yourself adjustment range from, say, 5 to 10 degrees, somewhere in there you'll find the right amount empirically (whatever is the right amount for comfortable self-centering of the wheel).

As far as bump steer is concerned (a change in toe-in during suspension travel changes), my understanding is that if you draw a straight line between the upper inboard a-arm pivot and the lower inboard a-arm pivot, the knuckles (ball-and-socket joints inside the rack boots) in the steering rack (BTW, the length of the outer arms is NOT a factor in bump steer, but IS in toe-in!) should center on this line. Other things are a factor too, of course, (for example, whether your rack is higher or lower than the steering arms on the spindles), but this one is the easiest to accomplish, and the most effective in reducing bump steer. I had to narrow my rack 2" for it to line up on this line, but moving the suspension fully through its travel results in no change of toe at all, ergo - no bump steer! 8) 8) 8)


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PostPosted: Sun Feb 11, 2007 9:05 pm 
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zetec7 wrote:
There's no way I know of to calculate the required castor angle - basically, if you make it adjustable (by engineering some way to move the upper a-arm fore-and-aft), and you leave yourself adjustment range from, say, 5 to 10 degrees, somewhere in there you'll find the right amount empirically (whatever is the right amount for comfortable self-centering of the wheel).


are we on the same page that if you are going with a tie rod upper balljoint that the only way to be able to adjust the upper ball joint forward or backwards for positive or negative castor is by putting adjustability at the chassis pickup points?

Do you see what i am asking in the last reply about whether to have the adjustable pickup points paralell or diagonal?


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PostPosted: Mon Feb 12, 2007 4:54 am 
Yep, that's it. I made my inboard a-arm attachment points adjustable, by having the inboard ends bolt to a bracket that can be slid forward or backward for adjustment. Coincidentally, they also have some up-and-down and tilt adjustability as well, which allows for anti-dive adjustment and extra fine-tuning of camber (normally this arrangement is tuned for camber by the use of shims under the inboard a-arm mounts, as per Mustang II design).

The adjustable pickup points are parallel, by the way (there are photos of my setup on my web page - the page takes a few moments to fire up, though).

I hope that helps...


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