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Old 12-20-2008, 05:39 PM
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Rear Triangulated 4 link set up

Greetings all, I'm trying to set up the rear suspension on my '37 Ford truck. It's a triangulated 4 link.

What I've done so far:
I have the rear centered/squared in the frame and welded temporary tabs to hold it at ride height so I don't/can't bump it out of position.
I had the 4 link tabs welded to the housing by Outlaw Performance, so they are in the correct place.
I've bolted the 4 link arms in to the rear housing brackets and have the front lowers clamped (not welded yet) to the bottom of the frame rails. The upper front mounts are just hanging there, not located/mounted yet.
I've made sure the lower arms are the same length, as well as the tops (shorter than the bottoms)

With the lower arms bolted to the rear end housing and clamped below the frame rails the lower links have an 8 degree drop going forward (front pivot lower than the rear pivot).

My quandary:
Should I just make the upper 4 link arms the same 8 degree drop? In essence having them be parallel to each other. The more I read about instant centers, wheel hop, over/under steering (how that relates to rear suspension set up still confounds me) etc just confuses me more.

I've looked at the charts/formulas from a few fellow posters here on the site, but I don't have some of the info that I think I need to "fill in the blanks".

As I don't have any mounting points on the frame for any of the link arms, I can put them where they should be, but I'd prefer to do it right the first time. Should I just make them all at a zero degree angle? I can pocket the bottom of the frame rail and move the front lower mounting point up to make it level.

I'm still building the truck, so I don't have a total weight of the truck to figure out any CofG.
I do have wheelbase: 112"
Rear tire height: 32"
Front tire height: 26"
I just haven't measured, but can get the length of the upper and lower arms.

I thought it would just as simple as putting the brackets to the frame and welding them on, just making sure nothing had a bind. Seems to be a little more complicated than that.

The truck will see basic street duty, towing a 6' x 12' enclosed trailer 4-5 times a year. It won't be drag raced, except for maybe the rare occasion.

Any simple guidelines to work with would be greatly appreciated.

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Old 12-20-2008, 07:36 PM
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If you angled the uppers down the same angle of the lowers the back end will squat a whole bunch under acceleration. Not the best solution. You either need to angle the uppers down a good bit more than the lowers or make the lowers flatter and angle the uppers down a bit less.
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Old 12-20-2008, 07:38 PM
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If I level out the lowers and keep the uppers at, say 8 degrees down in front, would I be ok?
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Old 12-20-2008, 07:57 PM
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That will actually give you some anti-squat as opposed to the pro-squat you would have with them both angling down at the same angle. How much...I don't know...not enough info. Take a SWAG at the CG (use cam height off the ground), plug it into the equations, and build it. If you don't like it you can always change it or even make multiple mounting bolt holes in hopes that you like the way one set works.
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Old 12-20-2008, 08:55 PM
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I was in the exact same situation as you when setting up my chassis, and like you became more confused the more information I got, So I can't explain why, but I have ended up with the lower bars level and the uppers slightly higher in the front. car drives and handles great. 120" wheel base,5.0 mustang setup converted to coil overs with aftermarket bars. have some frame pics in my photo album.

Last edited by Sixguns; 12-20-2008 at 09:31 PM.
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Old 12-20-2008, 11:19 PM
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If your setup is the type where the lower bars are parallel when viewed from the top, the angle of those bars in side view is very important as that is what determines the angle of the roll axis of this type of suspension. What that means in a nutshell is the closer to level the lower arms are, the higher the roll axis and the rear roll center tend to be. Without knowing the center of gravity of the car, you will just be taking your best guess as to what angle to install them (this much you know).

With the car at finished ride height, if you were to angle the lower arms up toward the front somewhere in the 3-5 degree range, and angle the uppers down toward the front a similar amount, that should get you in the range of 40-60% anti-squat. A good happy medium. If you were to make the frame mounts with multiple mounting holes you could play with the settings and see what works best for you. Adjust the bars for roughly 60% of the thread of the adjustable end is in the bar, make sure the pinion angle is correct, and that the tire is centered in the wheelwell before welding the mounts.

Andy
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Old 12-21-2008, 05:52 AM
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I copied the following from my post in another thread. The reference to "binding" was with regard to a NON-triangulated 4link.
*************

First, weight transfer is determined by total weight, CG height, wheelbase, and acceleration. Nothing more. The only thing left to "adjust" is just how much of that weight transfer is carried through the links and how much through the rear suspension springs. With 100% anti-squat, it's carried entirely through the links and the springs see none of it.

Having each link pair parallel is great, in that there is no binding during cornering, but, as you pointed out, you get excessive squat if the pair is also parallel to the ground. If, however, the links are parallel to the no squat/no rise line (100% anti-squat), you still avoid the binding and, at the same time, have no squat or rise. This requires an angle with a tangent equal to the CG height divided by the wheelbase.

I would say that 100% anti-squat is particularly important for a competition car, in that a rear end bobbing up and down means rear tire loads are also varying with time. For a street car, parallel links that are also parallel to the no squat/no rise line will result in some loss in ride quality. Placing the IC on the line at a height equal to the tire radius will restore ride quality, but, unless it's a triangulated 4link OR a 3link, binding is a problem.

The no squat/no rise line passes through the rear tire patch, with the effects reversed as the IC is positioned behind the rear axle.

I discuss these matters more fully at:

http://home.earthlink.net/~whshope
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Old 12-21-2008, 08:25 AM
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Alumnicraft, I installed an Air Rides Technology trianglelated 4 bar suspension in my 36 Ford PU which has the same frame as your 37. My front and rear tire diameters are the same at 28.5 inches. The front suspension is basically a Fatmans Mustang II. You can view and read about how I set this up by clicking on Project Journals and then clicking on Project Journals Archives when the page comes up. Then click on the picture of a Green and Black 36 Ford PU. If you could post some pictures of your work to this point, we may be able to offer more viable suggestions. From what I gathered from your post, you are going to have a severe nose down rake with the 32 inch rear tire diameter or you have modified your rear kick up or put a big C notch in the frame. With my 28.5 inch tires, I occasionally experience the frame bumping the rear axle housing.

I built my setup with the lower control arm parallel with the ground and the upper parallel with the lower. This was what ART instructions recommended and I have been very happy with the results other than the occasional bump. A small C notch would have taken care of that and I will get around to doing that in the future. My set up is a good ride and it seems to hook the 475 HP as good as could be expected on a 2600 pound pickup that is inherently light in the rear.

By the way, I will be starting a build of a 37 PU in the near future so would be interested in seeing all the pics and hearing your ideals you are entertaining.

Trees
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Old 12-21-2008, 10:03 AM
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Perhaps this article from a ten year old issue of Four Wheel & Off-Road magazine will answer all your questions.
http://www.4wheeloffroad.com/techart...t_2/index.html

If you are still confused feel free to ask more questions.
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Old 12-21-2008, 03:18 PM
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I stopped up at my shop and took some pictures of the rear suspension set up and measured a bunch of dimensions which I will post later tonight. I was working from memory as to what dimensions I needed, so hopefully I'll be able to plug them into the Excel charts provided by Triaged and BillyShope.

I REALLY appreciate all your input. The fog is starting to become a little clearer.
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Old 12-21-2008, 06:54 PM
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The way that I did this on my truck, a full custom frame and suspension, nothing factory. I set the truck at ride height on jack stands, and did the bottom bars parallel to the ground. Then I ran a string parallel to the ground and went to the middle of right behind the front bumper. I had the uppers set a little higher at the back, and angled them down to the same spot behind the bumper. I can't remember the exact numbers, but there was a few degrees of drop for the uppers. All I know is that I have 14" of lift with airbags, frame to 14" ground clearance, with no pinion change at all.

http://www.streetsourcemag.com/forum...topic_id=85853

Read that if there are any more questions, extremely helpful.
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Old 12-21-2008, 08:21 PM
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Here's some of the dimensions I took earlier today. One that I didn't think of until on the way home from church tonight was the front to back distance between the upper and lower front pivots. I have the arm lengths, but the top is around 45 degrees to the bottom, which is parallel to the frame rail.

Anywho, here are the dimensions I took today:
Upper arm length 15 1/2"
Lower arm length 23 1/2"
Rear pivots are 7 3/4" apart with the top about 1/2" forward of the bottom (which is centered under the axle)

Lower Arm mocked up with a 4 degree upward angle (back to front):
12 5/8" front lower pivot to ground
11 1/2" rear lower pivot to ground

Upper arm mocked with a 5 degree downward angle:
18" front upper pivot to ground
19" rear upper pivot to ground

First picture was taken with the 8 degree downward angle

second was taken with the rear pivot in the same place, but the front was raised to get a 2 degree upward angle

Third show about 3" of space available that I could lower the rear pivot down so I wouldn't have to have the front pivot so high on the frame rail. I'm thinking that the farther apart the vertical dimension between the front pivots the stronger the resistance to the rear housing changing the pinion angle, i.e. if the front pivots are the same distance apart as the rear pivots the pinion angle will stay the same thru the suspension travel.

I have my pinion angle set at 3 degrees up.
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Old 12-21-2008, 08:46 PM
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Here is the Photoshop rendering of what I'm hoping it will end up like. I've got to reduce the file size of all my other pictures down to the 300kb size to be able to show them.

If you want, I have a full folder of pictures over at Hub Garage
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