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Unread 12-11-2012, 12:52 AM   #1
stratostix
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Rear stretch shackle angle

Im in the planning stages of a 6" (or so) rear stretch. Im doing a lot of research on the subject but i'm finding conflicting opinions as far as shackle angle. In my current stock shackle location, my booms basically sit vertical. But i'm seeing some folks saying that once the stretch is done, the shackle should be sitting at a 45 degree angle when loaded. This makes no sense to me. I dont see how it should be any different when stretched. Anyone care to chime in?

PS: I should mention that i will keep my SUA set up for now. I'll also be using the same 4" lift YJ leafs. Basically relocating both shackle mounts and spring hangers rearward.

Thanks.

Edit: Perhaps that advantage would be increased droop?

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Unread 12-11-2012, 05:55 AM   #2
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What you are missing is that your current set up is not "right". It should be 45 degrees, stretch or no stretch
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Unread 12-11-2012, 06:01 AM   #3
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Quote:
Originally Posted by stratostix

Edit: Perhaps that advantage would be increased droop?
The goal of a suspension and travel is to keep the tires on the ground. Droop can allow the tires to drop enough to hit the ground. Only having a little uptravel is not as big of a deal as only having a little down travel.
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Unread 12-11-2012, 09:29 AM   #4
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particularly with a sua system you are hobbled by design with reference to droop. an exaggerated shackle angle can help. if your shackles will be mounted on the rear bumper you will definitely want a bit more angle so the shackles dont bottom out on the bumper itself at full droop. the too long shackle dilemma that bothers many people no longer pertains to you when moving mounts and doing a custom setup. use longer shackles and at an exaggerated angle. the fun part is its up to you.
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Unread 12-11-2012, 12:23 PM   #5
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Ok I understand the advantage. My boom shackles may actually already sit at a bit of an angle (the booms can look a bit deceiving in that respect) but definitely not 45 *
Anyways, I'll make sure to set things up accordingly. The way I see it now, the idea should be to have the shackles sit vertical at full droop then. Correct?
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Unread 12-11-2012, 01:03 PM   #6
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At full droop, the shackles usually point in on an angle
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Unread 12-11-2012, 07:02 PM   #7
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Quote:
Originally Posted by grandboost98 View Post
At full droop, the shackles usually point in on an angle
i guess i meant vertical-ish because i do understand that the shackle will naturally point inward. But i can't imagine the "inward" angle being that dramatic.
I'm pretty much the only leaf sprung jeep in my group so i rarely get to see how the shackles operate while i'm driving my own jeep. I can only imagine or look at pics.

Edit: I take that back. From looking at some of my wheeling pics, the shackle does seem to be almost inline with the spring at full droop.
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Unread 12-12-2012, 12:52 AM   #8
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Ok so i'm doing more and more brainstorming about how i wanna go about this....

We're talking about shackle angles so i did a little diggin and found some pics of how my rear shackles currently sit (my jeep is 60 miles away from me right now, cant actually look at it) and it looks like the rear shackles actually sit more or less vertical on level ground (front ones have more of an angle). Now, my initial plan was to keep my current springs and just move the spring mounts and shackle hangers back 5" to accomplish the stretch. Basically just moving the stock configuration 5" back.

But now I'm thinking, why not just relocate the spring mount 5" rearward but keep the stock shackle hanger location... I did some calculations and i figured that if I get some 6.5" (eye to eye) boom shackles made and sit them in the stock hanger location at the preferred 45 degree angle, i would be able to hook up the spring there with my 5" stretch (The angle and added shackle length would allow me to hook up the spring further back). 2 birds, 1 stone. Are you following? My only concern would be to make sure that the booms do not hit the crossmember at full stuff. What are your thoughts on this?

Edit: After doing even more research, it looks as tho setting the shackles at a 45* angle is better suited for flatter springs that arched ones. In that case, i'll be stickin to my original plan. Here's a link that might explain some of the reasoning behind this: http://www.pirate4x4.com/forum/jeep-...le-basics.html
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Unread 12-13-2012, 11:18 AM   #9
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that article is written assuming all other parameters are stock. this doesnt necessarily apply to you. example: longer shackles effect castor/pinion angle. true for a stock jeep false for everything else. the add-on post is complete crap and false.
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Unread 12-13-2012, 11:28 AM   #10
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Quote:
Originally Posted by fratis
that article is written assuming all other parameters are stock. this doesnt necessarily apply to you. example: longer shackles effect castor/pinion angle. true for a stock jeep false for everything else. the add-on post is complete crap and false.
It does make sense tho that the spring rate would stiffen for an arched SUA spring with a shackle sitting at 45*. Droop goes up, yes, but I'd be stiffening the ride. But I see how this would apply differently to a flat sprung SOA set up. Tell me if I'm wrong. I'm just trying to get a handle on this.

Edit: this is the reason why I'd rather sit my shackles at an angle closer to vertical for now. I don't care about the other stuff. Basically it's spring rate vs droop.
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Unread 12-14-2012, 12:42 AM   #11
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as long as the angle isnt exaggerated to the point of not allowing the spring to flatten out the angle itself has nothing to do with spring rate. you arent going to notice a difference in ride going from a shackle with an angle of 50* vs. 70*. dont know where that guy dug that up. makes no sense.
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Unread 12-14-2012, 04:02 PM   #12
stratostix
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Quote:
Originally Posted by fratis
as long as the angle isnt exaggerated to the point of not allowing the spring to flatten out the angle itself has nothing to do with spring rate. you arent going to notice a difference in ride going from a shackle with an angle of 50* vs. 70*. dont know where that guy dug that up. makes no sense.
Right. As long as the shackle can swing back far enough to flatten out the spring. That makes absolute sense. Thanks for the feedback. It all makes more sense now. I'm gonna go ahead and do some math now
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Unread 01-18-2013, 08:08 PM   #13
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Ok I've been planning this out as well, and I haven't seen anything on length of shackle?

I'm planning on switchin back to stock length boom shackles, but I don't want to have to switch them again with longer ones when I do my stretch.
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