Geometry correcting pins for Fabcar control arms
05-20-2007, 10:43 PM
#1
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Geometry correcting pins for Fabcar control arms
I'm looking at having some "geometry correcting" pins made up for Fabcar control arms. These would essentially be 1" longer than stock, so with a car that's lowered, the control arms would be about in the original factory position.
This will raise the roll center on lowered cars, improving the handling characteristics.
Along with these longer pins, a bump steer kit is also required -- which I'm looking at having fabricated, too. On 944s you always want the steering tie rod parallel with the control arm -- this way, as the control arm swings through its arc, the tie rods swing along an identical arc. Otherwise, when the suspension is compressed, your toe in/out settings will change, creating "bump steer".
If anyone else is interested in such a setup, let me know. If I can get enough people interested, we'll get a small price break. I don't have all of the figures in yet, but I expect the kit will cost about $800 (control arm pins, new tie rod ends and steering knuckle pins).
I don't know the size of the Charlie Arm mono-*****, but if the bore is 1", then these would also work. I know the Racer's Edge control arms are NOT 1" dia, but I also know that Racer's Edge has a geometry correcting kit (although I don't think they have a bump steer kit -- if they do, let me know, and I won't waste my time on that!)
This will raise the roll center on lowered cars, improving the handling characteristics.
Along with these longer pins, a bump steer kit is also required -- which I'm looking at having fabricated, too. On 944s you always want the steering tie rod parallel with the control arm -- this way, as the control arm swings through its arc, the tie rods swing along an identical arc. Otherwise, when the suspension is compressed, your toe in/out settings will change, creating "bump steer".
If anyone else is interested in such a setup, let me know. If I can get enough people interested, we'll get a small price break. I don't have all of the figures in yet, but I expect the kit will cost about $800 (control arm pins, new tie rod ends and steering knuckle pins).
I don't know the size of the Charlie Arm mono-*****, but if the bore is 1", then these would also work. I know the Racer's Edge control arms are NOT 1" dia, but I also know that Racer's Edge has a geometry correcting kit (although I don't think they have a bump steer kit -- if they do, let me know, and I won't waste my time on that!)
05-20-2007, 11:16 PM
#2
Racer
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BTDT! The results were not good. 4140 failed, and then 4340 failed. It is obviously very dangerous when these pins fail.
Also the tie rod relocation ruins the steering feel because you have a long flexy bolt in single shear.
I love Solidworks!
Also the tie rod relocation ruins the steering feel because you have a long flexy bolt in single shear.
I love Solidworks!
05-20-2007, 11:35 PM
#3
Rennlist Member
Chris - do remember where the pin failed at - at the bj knuckle, the control are joint, etc? I wonder if you could go with a 19mm pin like the Charlie arms to help strengthen the pin. The guys at Worldwide Motorsports ran longer pins on their Charlie Arms apperently without problems - I was considering getting a set from them for my Charlie arms but am still evaluating the risk vs. reward. As you said - high cost of failure.
05-20-2007, 11:57 PM
#4
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Thread Starter
Can you enlighten me as to what BTDT means?
I was contemplating 19mm pins, but I'm afraid that'll induce new problems (see pic).
Does anyone know situations where the Fabcar pin has failed? I personally have seen two accidents involving side impact front collisions (my parts car that a PT Cruiser squaffled -- bending a Fabcar control arm and breaking the strut; and a recent track accident I had that bent the strut). Anyhow, in both situations, the control arm pin did NOT fail (but, needless to say, they weren't/won't be used again).
Solidworks is nifty, but I'm still getting the hang of it.
I was contemplating 19mm pins, but I'm afraid that'll induce new problems (see pic).
Does anyone know situations where the Fabcar pin has failed? I personally have seen two accidents involving side impact front collisions (my parts car that a PT Cruiser squaffled -- bending a Fabcar control arm and breaking the strut; and a recent track accident I had that bent the strut). Anyhow, in both situations, the control arm pin did NOT fail (but, needless to say, they weren't/won't be used again).
Solidworks is nifty, but I'm still getting the hang of it.
05-21-2007, 08:21 AM
#5
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BTDT= Been There Done That!
The pins break where the radius is to neck the pin down to 17mm (or 19mm)
I think that the Fabcar pin is well designed but when you increase the length you increase the bending stress. This stress is cyclical and eventually the part fatigues and breaks.
I was shocked at how quickly they broke.
The nature of fatigue failures in steel parts means that basically the harder you can corner and brake, the faster the part will fatigue. Below a certain level of grip, however, the part will never fatigue. Our parts must be designed so they operate in this range.
A better solution would be to make a proper tapered ball joint pin that fits into a Fabcar or Charlie arm, and then make a billet spindle assembly that fixes the geometry problems and gets rid of the tiny wheel bearings and weak hubs.
Not easy or cheap.
The pins break where the radius is to neck the pin down to 17mm (or 19mm)
I think that the Fabcar pin is well designed but when you increase the length you increase the bending stress. This stress is cyclical and eventually the part fatigues and breaks.
I was shocked at how quickly they broke.
The nature of fatigue failures in steel parts means that basically the harder you can corner and brake, the faster the part will fatigue. Below a certain level of grip, however, the part will never fatigue. Our parts must be designed so they operate in this range.
A better solution would be to make a proper tapered ball joint pin that fits into a Fabcar or Charlie arm, and then make a billet spindle assembly that fixes the geometry problems and gets rid of the tiny wheel bearings and weak hubs.
Not easy or cheap.
05-22-2007, 08:30 AM
#7
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Thread Starter
Originally Posted by Schuepbach
all you need to do now is import that solid works file into patran and run a stress/strain analysis on it
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05-22-2007, 12:30 PM
#9
Race Director
Originally Posted by Premier Motorsp
BTDT= Been There Done That!
The pins break where the radius is to neck the pin down to 17mm (or 19mm)
I think that the Fabcar pin is well designed but when you increase the length you increase the bending stress. This stress is cyclical and eventually the part fatigues and breaks.
I was shocked at how quickly they broke.
The nature of fatigue failures in steel parts means that basically the harder you can corner and brake, the faster the part will fatigue. Below a certain level of grip, however, the part will never fatigue. Our parts must be designed so they operate in this range.
A better solution would be to make a proper tapered ball joint pin that fits into a Fabcar or Charlie arm, and then make a billet spindle assembly that fixes the geometry problems and gets rid of the tiny wheel bearings and weak hubs.
Not easy or cheap.
The pins break where the radius is to neck the pin down to 17mm (or 19mm)
I think that the Fabcar pin is well designed but when you increase the length you increase the bending stress. This stress is cyclical and eventually the part fatigues and breaks.
I was shocked at how quickly they broke.
The nature of fatigue failures in steel parts means that basically the harder you can corner and brake, the faster the part will fatigue. Below a certain level of grip, however, the part will never fatigue. Our parts must be designed so they operate in this range.
A better solution would be to make a proper tapered ball joint pin that fits into a Fabcar or Charlie arm, and then make a billet spindle assembly that fixes the geometry problems and gets rid of the tiny wheel bearings and weak hubs.
Not easy or cheap.
Guys, I agree with Chris here. Both from a theory persective on the longer pin AND I trust his experience with 951 from years ago. LISTEN TO HIM!
05-22-2007, 01:06 PM
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Originally Posted by evil 944t
Van, solidwork's Cosmos program can stress test it too.
oooh forgot about that too, i don't know much about solidworks, basically you need create a mesh, add constraints, and add forces. Also dont forget to enter material properties
05-22-2007, 06:15 PM
#11
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Wow, the COSMOSMotion software looks great, if any of you do a suspension simulation for the 951, please share your findings.
http://www.solidworks.com/pages/prod...Suspension.pdf
Also, does anyone make an aftermarket Caster adjustment pin for the 951?
It would be nice to try more caster than the stock 3 deg...
http://www.solidworks.com/pages/prod...Suspension.pdf
Also, does anyone make an aftermarket Caster adjustment pin for the 951?
It would be nice to try more caster than the stock 3 deg...
05-22-2007, 07:40 PM
#13
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Thread Starter
That car was an ebay find. A PT Cruiser ran a light... Your guess at speed is as good as mine, but probably 45+ MPH.
The driver and passenger of the 944 walked away with just scratches and bruises.
BTW, I've gotten enough negative feedback about extending the control arm pins, I'm going to abandon that project for now. If anyone has any other ideas, let me know.
I did, I think, come up with a good design for a bump steer kit, however (see pic). By using a pin (green part) that will be in tension and a sleeve/standoff (brown part) that will be in compression, I think it would be even be more solid than the current tie rod end -- eliminating any flexing that Chris mentioned a concern about earlier.
The driver and passenger of the 944 walked away with just scratches and bruises.
BTW, I've gotten enough negative feedback about extending the control arm pins, I'm going to abandon that project for now. If anyone has any other ideas, let me know.
I did, I think, come up with a good design for a bump steer kit, however (see pic). By using a pin (green part) that will be in tension and a sleeve/standoff (brown part) that will be in compression, I think it would be even be more solid than the current tie rod end -- eliminating any flexing that Chris mentioned a concern about earlier.
