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Old 07-17-2006, 01:35 AM
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Rear air suspension design

Here's a look at my triangulated 4 link air spring design. The control arms are made from 3/16" wall 1 1/2" tubing with a 7/8" NF nut welded to one end for adjustment, and a 7/8" bolt threaded in with a section of tube welded to it to hold the bushings. I got tired of the expensive and tiny street rod poly bushings and used poly bushings for a 70's Chev rear leaf springs. They are beefy and use 9/16" bolts - Energy Suspension has them in packages of 6 so I got two packages and used a couple for engine mounts too. They look tidy and work excellently. I mounted the air springs ( Universal Air, double convoluted )on the lower control arms, this provides more travel, and used shocks for a lifted 70's Chev blazer for almost 10" of travel. The triangulated setup does eat up space but doesn't require a Panhard bar to locate it. I used a 4" single exhaust setup to help ease the space issue and mounted the shocks behind the axle. This arrangement rides super with only 45psi and handles very well. Up front I used Universal Air single convoluted springs mounted to pedestals welded to the axles. Moving them inboard from the stock coil spring location increases the wheel travel for a given amount of spring travel. By the way, if you don't recognize it, the front end is from a 78 Ford F150, twin I-beam. I used it for it's appearance - kind of like an old axle-beefy construction, 11 1/2" discs, easy to mount and there's a million of them out there for cheap! The older ones also use a nicer looking forged trailing arms or hairpins or you can fabricate your own hairpins maybe using those two spare rear poly suspension bushings to mount them at the rear. It is a bit wide for most applications but since the axles are forged steel, shortening them would not be a problem. In this setup, I tweaked the end that mounts to the pitman arm to work with the GM steering box. Flaming River seems to think this is their own brilliant new idea with their new Dominator front end kit but Ford used it for over 30 years!
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Old 07-17-2006, 07:13 AM
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VERY VERY NICE WORK! thanks for posting those photos, you work clean and on a budget, I like that 10X more than your high buck hot rods.... This is not criticism just a word of caustion (for your agrivations sake) I noticed your using the festo fittings on your bags... (this is just my personal experience) I have helped multiple rodders in my area get rid of their festo's all of em work great for the first little while but it seems like as the vehicle gets more time under its belt (driven) the vibration and pressure cycling tends to make em leak, and I'm not talking about a onsey twosy leak....for example the most recent truck we converted to brass pressure fittings. When the truck was first built it would hold its pressure for over 5 days, a month after it would cycle the compressor on after 1 hour....thats some serious leakage. we changed the festos out....no problems....just keep an eye on it...beutiful work!
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Old 07-17-2006, 07:37 AM
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I agree, very nice work. My only concern would be the poly bushings with the rather large lateral distance between the rear mounts of the upper links. The total elimination of binding while cornering, with a triangulated 4link, is only obtained with a true "V" arrangement. I'd suggest you monitor the wear on the poly bushings and, if excessive, switch to rubber.
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Old 07-17-2006, 01:58 PM
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Very nice work. I like how you used a HUGE single exhaust to clear all of it. It sure does look very well packaged. It looks like your front wheels could use a bit more backspacing to help out the steering geometry.

How much does your camber and caster change with ride height? I think you will have a very small range of where the front end can be while driving and not kill the tires.

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Originally Posted by BillyShope
My only concern would be the poly bushings with the rather large lateral distance between the rear mounts of the upper links. The total elimination of binding while cornering, with a triangulated 4link, is only obtained with a true "V" arrangement.
I have heard this in more than a few places but I don't think it is correct. The reason that the suspension binds up in roll/articulation is because of the bushings (poly or rubber) not wanting to let the link twist (you will need half the roll angle worth of twist in the bushings at each end). If spherical rod ends are used on a suspension like this there will be no binding whatsoever (but I don't think a street car is a good place for rod ends). This can be evidenced by the offroad guys getting 45deg of articulation (as long as you don't run out of angularity in the rod ends).

The binding because of the bushings would be the same for any other 3 or 4-link suspension (3-link binding less only because it has fewer bushings to twist). The recent way the factory has gotten around this is to use bushings with voids in them to reduce their influenced on the roll stiffness while still keeping the same front to back stiffness.

...but hey. Just think of it as already having an anti-roll bar on the back end
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Old 07-17-2006, 02:04 PM
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I was going to ask what body you were going to put on that work of art...but then I looked in your project journal...The body looks even better than the chassis. Too bad you live so far away. I would love to see that thing up close. That truck has it all (I wasn't expecting to see a truck body)!
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Old 07-17-2006, 04:55 PM
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Quote:
Originally Posted by Triaged
. The reason that the suspension binds up in roll/articulation is because of the bushings (poly or rubber) not wanting to let the link twist (you will need half the roll angle worth of twist in the bushings at each end). .
Binding, while cornering, can occur due to bushing bind and/or due to the linkage configuration. A 3link with Heims will not bind, but, if the Heims are replaced with bushings, there will be some bushing bind. A competition (non-triangulated) 4link will always bind, even when fitted with Heims, unless each link pair (right and left) is parallel OR unless one of the rear brackets is allowed to rotate on the axle housing. (The latter is done with oval track cars, but I've never seen it on a drag car.) When the two links of a link pair are parallel to each other, the angular relationship between the end brackets remains unchanged through full suspension travel. If, for instance, they are not parallel and the instant center is a finite distance forward of the rear axle, bind will always occur. Consider such a situation with the car turning left. Picture yourself looking at the rear suspension from the right side of the car. As the right rear wheel moves up, the right side links are attempting to rotate the rear axle housing in a clockwise direction about the instant center. On the left side, however, the linkage is attempting to rotate the housing in a counter-clockwise direction. This is linkage bind and has nothing to do with the use of Heims or bushings.

A triangulated 4link is essentially a 3link with the upper link splayed out to accept lateral loads. But, the more you separate the link ends at the crotch of the "V," the more it begins to bind like the competition 4link. I considered the suspension pictured to be "borderline," as far as causing trouble is concerned, hence my warning.
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Old 07-17-2006, 08:33 PM
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Kallie49

Thanks for the tip on the fittings, I assume you mean the plastic push fittings. So far no problems - the were all the local supplier had at the time, I've found it hard to come across anyone locally who is dedicated enough to stock or supply a decent range of fittings.
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Old 07-17-2006, 09:06 PM
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To; Triaged, re- front suspension

Yes, camber and castor does change as it does with all Fords with the twin I-beam front end. With the stock coil springs you have no control over ride hieght and over time as they settle, tire wear can be a problem - even carrying a load affects the front end ride hieght. However, with the air springs you simply adjust the pressure for optimal geometry and go with that, and if it is too high a pressure for a good ride, simply shim the lower mount to change the operating range of the spring and change the bumpstop hieght accordingly.
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Old 07-17-2006, 09:39 PM
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To; BillyShope re- rear suspension design

As to my setup being of a "borderline" design, I would say take a look under countless Ford, GM and Mopars sometime. They all have used variations of this design. Mine works and tracks just great, thanks.
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Old 07-17-2006, 09:53 PM
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Quote:
Originally Posted by ccrodder
As to my setup being of a "borderline" design, I would say take a look under countless Ford, GM and Mopars sometime. They all have used variations of this design. Mine works and tracks just great, thanks.
But, they use rubber bushings. I tend to be overly cautious on such matters, so you might never have any trouble. Still, if you're not going to use rubber bushings, I'd feel a lot better about it if you had been able to get those bushings closer together. Functionally, I'm certain you'll be quite happy with your present arrangement.
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Old 07-24-2006, 01:57 PM
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AirRide

CCRodder,
Very nice job on the frame etc.. I was wondering if you are going to use any type of load leveling device? I bought an AirRide Pro e system last year and have installed all of the hardware but the body is still not done so it's not on the street. AirRide came out with a leveling system but guess what, it won't work with the Pro e, only the Pro e 2 system. Of course for another $1200 you can change the old to the new. The old hasn't even left the shop yet and I don't feel like shelling out that much money for something I already have so I was wondering if you were using anything on your project?
Thanks,
Jim
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Old 07-24-2006, 11:05 PM
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Load levelling

Nah, I wasn't going to use a load levelling or "memory" system. More gizmos and wiring to mess with. I kind of just like to play with to ride hieght manually rather than giving over control to the evil computer...
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Old 07-24-2006, 11:14 PM
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Quite honestly (and I asked these questions when I put mine in cause I was looking at the computer memory systems as well) I was told to drive it without the memory system in place, get used too it and then make a decision on whether or not to install it....once you get used to your system you just know where you are sitting relative to your suspention, seeing as I was advised that the more fittings and sensors you have the more that there is to leak and maintain (and to brake which makes perfect sense to me anyway) I chose to not install the computer stuff....plus that kinda gear gets really expensive really fast....thats just my opinion tho...each to his own
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