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Old 02-06-2008, 11:47 AM
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Performance and wishbone style suspension

Figured I'd post up this question too since I got such great help with previous questions. So my setup is really confined on my project and I'm doing a bunch of things at once, basically it's a 2001 Silverado I'm building it for performance, but also bagged and body dropped for that matter, so I need the lift, so shockwaves are out, (for now) plus I will be running upwards of 15" wheels out back so the frame is narrowed, with a 14 bolt rear end (big center section) inboard 4link bag placement shocks and the need of a center device (panhard) so to eliminate the clutter I contemplated running a 3 link suspension, two parallel bars on the bottom of the axle then building a cross bar right over the center section and have the upper bars meet there with a Johnny Joint.

Now my question is what negative effects can I get from running a 3 link wishbone instead of parallel 4 link and pan hard?

It's not a strict drag truck, but will see the strip every once and a while, but I still want to cruise the streets and have fun on corners.

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Old 02-06-2008, 12:09 PM
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Johnny what??

Hey ,Id like to help but do not know what a JohnnyJoint is???? (let me know) I just know that to keep rear axel housing from twisting, you need to have mts above and below the axel line, and a good panhard bar with wide back tires. good luck. ACE
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Old 02-06-2008, 12:30 PM
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Johnny Joint is like a heims except using a bushing around it, so it combines a bushing and a heims for superiority, and I know where the links have to be, just want to know the disadvantage of a parallel to a wishbone, I shouldn't need a pan hard with a wishbone, so I'm not sure what you were getting at.
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Old 02-06-2008, 02:04 PM
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There is no disadvantage to using a 3 link for your purpose. Do a search on the site here for 3 link and there are a few threads that can explain the dynamics of the 3 link vs 4 link with panhard bar..

You can also use a triangulated 4 bar and get the same effect, but it is a bit stronger than a single joint/wishbone at the top.

The only disadvantage I can see would be in exhaust routing...you run out of room with shockwaves, long travel and big exhaust pretty fast if you want a rear exhaust.

Later, mikey
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Old 02-06-2008, 03:44 PM
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thanks, and wow I just spent 4 hours reading this site full of stuff and finding links, for other sites and ready to get a calculator and set this thing up perfectly. Thanks guys!
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Old 02-06-2008, 06:27 PM
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I guess my main concern is that one bushing preventing all the side to side movement, call me skeptical. I was planning on putting the lower bars parallel then the upper bars meeting above the pumpkin (on a cross bar that is bent up and around the pumpkin) Is the wishbone seriously legit enough to put through high horse power? Or am I back at square one trying to fit 10lbs of crap in a 5lb bag?
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Old 02-06-2008, 11:28 PM
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Quote:
Originally Posted by GMracer
I guess my main concern is that one bushing preventing all the side to side movement, call me skeptical. ?

Triangulated 4 bar uses 8 bushings total.

It's stronger than 7 bushings.


later, mikey
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Old 02-07-2008, 06:54 AM
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I don't know squat about bags and all that...but..

Performance? on a wishbone style? Do you mean super long trailing arms going super long near the front u-joint?

If so, just copy the Nextel Cup cars rear arm setup..they are performance cars, right?

They use 60-66 chevy truck trailing arms Nascar has used those stock chevy arms forever
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Old 02-07-2008, 09:47 AM
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I'm talking about lower parallel links like a 4 link then a wishbone so the upper bars meet at one point above the center chuck and then angle out and mount above the lower link frame mounts I'll draw up a picture later to explain, it doesn't really matter about bags I'm just curious about the strength of this system.

I know triangulated has 8 bushings, so I may end up with that, but I figured if a wishbone setup was strong enough I would do it.
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Old 02-07-2008, 03:11 PM
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I don't think the difference between 7 bushings and 8 bushings will be significant. The highest load point will be the single connection at the top of the differential and we can calculate what that load will be.
Let's start with some basic assumptions, your engine can produce 500ft:lb of torque, first gear is a 3:1 reduction and for simple math you have a 4:1 reduction in the rear end. Let's also assume the center to center distance from the axle centerline on the rear end to the wishbone connection is 1.0 feet (12 inches). Under those conditions and not accounting for any mechanical loss the torque delivered to the rear wheels will be 500 x 3 x 4 = 6000 ft:lbs. The force delivered to the top link will 6000 ft:lbs / 1.0ft = 6000lbs.
Ultimately the real torqe applied to the links will be limited by your tire adhesion and even at 6000lbs when you consider the tensile strength of steel a reasonably sized link will have ample strength.
Just as a point of interest the force on the bottom links would be Torque divided by the distance from the lower link to the axle and that divided by two because there are two lower links.
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Old 02-07-2008, 04:17 PM
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That's fine if you only consider slowly applied linear stresses. Aren't shock loads calculated at several times the static loads?..Also, with one link at the top doing all of the work in locating the rear end laterally, which is a side load and the twisting that occurs during regular driving, you have 1 joint doing alot of work, and it would not be all that hard to divide the loads between 2 upper rod ends..



I'm no engineer, but I know that depending on 1 part to do the work that most use 2 joints for is asking for trouble, IMO.

I also know that people are doing it, and making it work. I'm just stating my opinion on that type of suspension.

Later, mikey
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Old 02-07-2008, 04:24 PM
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both you guys make very good points, I agree with you above above launching but side to side? like the next guy states is what I'm really worried about
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Old 02-08-2008, 01:30 AM
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Mikey was correct in saying my calculations did not acount for all of the forces, it was intended to give a feel for the magnitude of the forces involved and I should have made that clearer. For the most complete discussion of rear suspension design I have ever seen you should go to Billy Shope's website and poke around. http://home.earthlink.net/~whshope/
If space is at a premium it is possible to design a 3-bar setup that is safe and will perform well. Weigh all the factors, make your choice and get busy.
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Old 02-08-2008, 06:31 AM
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Yea I found his site, very informative. I'm not limited on space to the point I couldn't fit a parallel so a 3 bar is pointless because I still need a centering device, and if I run a pan hard or Watt's my bag and shock situation would be compromised. So I was trying to figure out if it'd be beneficial to just run one link (wishbone) or two links triangulated 4 link.

The only way I may be able to run a parallel setup is if the pan hard goes directly over the over, but then I run into clearance issues why I lay out, and would have to cut the bed floor, I already am raising the bed floor to hide everything, but I don't want to have to raise it more than I already have to.
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Old 02-08-2008, 06:48 PM
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well I stopped by a local chassis guy (who is narrowing my rear end) and we decided for my setup it'd be best suited for a triangulated 4link with the upper bars pointed towards the front. so I guess that is my final decision.
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