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Old 02-20-2004, 10:55 AM
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Question Suspension from scratch?

Im helping a buddy build a frame and suspension for his Avenger (FiberFab GT40 Kit Car). The original plans call for Corvair front suspension. He has decided to go with something of our own, based on what a lot of Street Rodders do, a Mustang II style front with coil over shocks. Heidts nor Fatman have anything available for such a kit car. I have laid out on CAD the framework, Mustang II spindles, rotors, rack, tie rods and lower control arm and now we want to fasten everything. I still need to figure our how to do the upper A arm and figure out which length coil over we need. Ive measured Mustang II upper A arm mounts and it seems as though they (shaft) are laid back 7 degrees. We want to use some over the counter A arms but I have no idea what the centerline distance is between the two parallel legs that make up the U shape of the A arm? We want to use rod ends on each end of the A arm for adjustment. To fasten to the frame it will have a long bolt through one rod end, through a tube welded to the frame on the 7 degree angle, through the other rod end and nutted with bushings of course. We want to use the wide type lower A arm but have no idea on the distance between the two parallel legs are? On the wider style, lower A arms do you still need to use a Strut Rod? We are setting it up with the lower A arm parallel to the ground but does the upper one go parallel or have some angle. We clipped off a Mustang II front end for measuring but are not going to use it, it was just for reference, this is where most of our dimensions have come from. How to calculate coil over length? We run dirt track stock cars here in PA and are using some of our brain power from that and are applying it to the kit car (maybe no a good idea!). The above questions are all that we have left (I think!). Any help is greatly appreciated and I hope I am able to get my questions across without too much confusion. Are there any web sites out there to help on building a suspension from scratch?

Thanks,

Doug Bender
1966 Fairlane 390/C6

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Old 02-20-2004, 12:08 PM
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If you E-mail your cad file in dwg format I might be able to help you with the design.
Walt
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Old 02-21-2004, 08:31 PM
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Thanks

I appreciate your offer, what kind of help are you offering? Do you have knowledge of some of the dimensions that I need?

Thanks,
Doug
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Old 02-22-2004, 10:40 AM
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Hey Doug... Cool project you have going here...
If I can make a few suggestions...?
The 7 degree angle on the upper arm shaft is mostly for anti-dive.
Instead of welding your tube solid for the "A" arm mount use an adjustable cross-shaft which uses spacers for Camber adjustment and slots in the arm mount welded to the frame for Caster and Anti-Dive adjustments. This method is much easier to adjust then using rod ends which requires the upper bolts to be removed every time it needs to be adjusted.
If you can get one of the aftermarket suppliers to provide dimensions you will be lucky. I would just buy the pieces you want to use and design right from them.
The upper arm inclination (whether up or down) determines roll center which is a compilation of trajectories shot through all of the suspension points. King Pin axis, upper and lower ball stud centers and inboard bushing points all effect the articulation of the suspension.
If you use off the shelf components and design to a current suspension "BUCK" you really shouldn't have to be concerned with most of these issues.
Mark
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Old 02-22-2004, 11:52 AM
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If you want to duplicate the factory setup just measure a stock one in the junkyard...but for all the trouble you have gone through and the redesign you are attempting I would just go with parallel arms with the proper caster put into the offset of the upper arm. I would also just weld up you own arms instead of adapting stock pieces, that way you can utilize off the shelf tie rod ends with the threaded interface already tapped in the tubes before welding.

All the other factors you are discussing are part of chassis design and have specific purposes for being there, if you want to know why I suggest you pickup a book called Race Car Engineering and Mechanics, it explains all the factors and gives you a good understanding of the components and how they interact and the geometry changes possible.

It's pretty hard to go wrong with a simple tie rod end parallel link arm and aftermarket spindle setup, you could spend a lot more adapting a factory setup if you account for your time and labour.
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Old 02-22-2004, 08:26 PM
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Re: Thanks

Quote:
Originally posted by fairlaniac390
I appreciate your offer, what kind of help are you offering? Do you have knowledge of some of the dimensions that I need?

Thanks,
Doug
I have designed many IFS units from Mustang II to scratch built. I have many of the dimensions from stock and aftermarket parts. Most of what your doing will be determined by the componants that you are using and the frame that you're fastening it to. If you are using a stock width Mustang Rack, spindels and lower a arm lenght then the upper a arm angle and length will also have to be the same as Mustang. The angle of the upper a arm, To the ground, will determin what roll center that you have established. The wide lower a arm does not need an additional strut rod.
Like I said..... If you e-mail your cad file I can probably help. Walt
walts@sonic.net
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