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Old 04-13-2006, 06:40 PM
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Advise about building my own 4-link

SuicideDoors.com has parts to build your own 4-link for what ever. Im wanting to put one together for my 76 GMC, swb, 2wd, pu. The ? is, they sale different length tubes, an 1" od 18" 24" 30" 36", and a 1.5 od 18" 24" 30" 36", which of thiese tubes lengths should i consider for my application? If anyone has some input, on building a 4-link, it would be much appreciated. As far as frame work goes, all the spring hangers were removed last year, when i painted the frame with POR-15, and were just bolted back inplace. H*ll i even took out the big cross member, in the middle of the frame, so i could get behind it, and bolted it back in. So now im planing to do a 4-link. They have all the brakits to use for this project, i only need some kind of an idea of how long the lubes should be. (Please Advise)
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Old 04-13-2006, 08:02 PM
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I moved this to suspension for more answers to the questions.

thanks.
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Old 04-14-2006, 06:26 AM
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While you might be ahead buying some of the brackets and bushings at the site, I certainly wouldn't buy the tubing when they don't even tell you the wall thickness. You can buy the tubing at any material supplier. I'd use mild steel and go heavy on the wall thickness. Doesn't make that much difference in weight and it's your life we're talking about. You're not building something for Formula One.

Link lengths should be as great as conveniently practical. This minimizes angle changes as you encounter irregularities in the roadway.

As for bushings, you might consider going to a shop that rebuilds leaf springs. The Mopar rubber bushings work quite nicely. If you insist on adjustability, use Heims only where needed.

And, why a 4link? You really only need 3 (and a Panhard, of course). Go to page 6 at:

http://home.earthlink.net/~whshope

and you'll find a setup spreadsheet for the 3link which will give you dynamic cancellation of the driveshaft torque. In other words, whatever the driveshaft torque, the rear wheel loading...left to right...will be equal.

If you choose a 3link with a single lower link, be particularly careful about the strength of that single link. If you can picture 6 copies of your car, stacked vertically atop that single link without it failing, then the link is probably strong enough.

If you insist on a 4link, there is another page, at that same site, which has setup instructions for the same kind of dynamic driveshaft torque cancellation. This does, however, yield some roll oversteer, which you might find objectionable. (The "oversteer" in roll oversteer is somewhat of a misnomer, since wheel loadings, while cornering, are unaffected and, therefore, the stability parameters remain unchanged. Steering wheel angle changes, however, mimic those associated with "true" oversteer and can trouble some drivers.)
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Old 04-14-2006, 09:05 AM
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Quote:
(The "oversteer" in roll oversteer is somewhat of a misnomer, since wheel loadings, while cornering, are unaffected and, therefore, the stability parameters remain unchanged. Steering wheel angle changes, however, mimic those associated with "true" oversteer and can trouble some drivers.)
You said that right!
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Old 04-14-2006, 07:38 PM
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ThanX for the info, i believe you kind of talked me right out of building the 4-link.
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Old 04-15-2006, 06:14 AM
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Dude,
I built my own 4-link for the rear. I used two pieces of 2x4 square tubing for the rear brackets. I cut holes in them for the axles with a 3 inch hole saw. The front brackets were already welded to the frame or I would have made them. I also bought a used straight axle and the bars were too short for the brackets that came on the frame so I chose to have new bars made that were longer. Speedwaymotors.com has lots of parts also such as heims and bushings and such. Just remember that someone already mentioned tubing wall thickness. I'd go with at least 1/8 inch wall thickness. More than that is probably overkill as the heim threads will give before the tubing.

Last edited by gasser34; 04-15-2006 at 07:14 AM.
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Old 04-15-2006, 11:48 PM
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This is something I made up a few years ago. By now 100's of guys have used it do help them design their suspensions.
http://www.pirate4x4.com/forum/showthread.php?t=204893

As for tubing sizes and wall thickness...
Offroad guys are quite abusive. Some guys have problems bending 2" OD x .500" wall hardened Chrome-Moly steel

If you plan on putting the 'bags on the lower links you will need them to look more like a "truss" than a "link".
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Old 04-16-2006, 05:57 AM
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My comments on wall thickness were based on loads imposed by drag slicks. As Triaged has noted, offroad requirements can be even more stringent. And, when you go from 4 links to 3, it follows that loads are increased. This is particularly true when the "odd" link is below, where required wall thickness, with a typical car, would most likely be far more than 1/8 inch. A specific application would require a study of the relationship between tubing diameter, wall thickness, weight, weldability, and availability.
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