rear 3 link design help - JKowners.com : Jeep Wrangler JK Forum
 
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post #1 of 18 Old 12-23-2011, 05:17 AM Thread Starter
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rear 3 link design help

I've been searching on the net for a answer but just keep coming up with 3 link calculators. Is there like a % to go by when building a 3 link. I read somewhere 70% not sure if that's right. Need to know if the upper link is supposed to be equal or less to the lower links. Right now from eye to eye the lowers will be at 39 inches. Need to know where to set the upper at. I measured and I can get a 37" upper under there just barley. But was thinking it might need to be shorter then the lowers like 32"s or around that. Any help I appreciate it.
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post #2 of 18 Old 12-23-2011, 08:16 AM
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Sir

Are you talking about running an independent 3 link with a track bar or are you talking about a "tri-link" rear that removes the rear track bar?

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post #3 of 18 Old 12-23-2011, 09:02 AM Thread Starter
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3 independent links and track bar. Similar to your design. I'm using the currie bridge and have my lower mounts welded up on the frame kinda like the RE long arm kits. The lowers are going to be 39"s. I was just under there again and i measured the upper for 30"s that's 9" difference. Think that would be ok to go with? I might be able to go a couple inches longer on it.
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post #4 of 18 Old 12-23-2011, 09:11 AM
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I will just post up my results:

Lowers: 31"
Upper Centered 3-link: 29"
Trackbar/Factory Currie Length
16" coilovers 5" up/ 9" down

I never use calculators as they depress me.
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post #5 of 18 Old 12-23-2011, 10:06 AM Thread Starter
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Quote:
Originally Posted by cjcraig7 View Post
I will just post up my results:

Lowers: 31"
Upper Centered 3-link: 29"
Trackbar/Factory Currie Length
16" coilovers 5" up/ 9" down

I never use calculators as they depress me.
So you are only at a 2" difference... I'm still not sure if having a shorter upper link will affect how the pinion angle will stay while going though the suspension cycle. Two inches is not much at all. How do you think 6 to 9inches of difference would do? Think the angle would stay in check?
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post #6 of 18 Old 12-23-2011, 10:45 AM
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Quote:
Originally Posted by frankie945 View Post
So you are only at a 2" difference... I'm still not sure if having a shorter upper link will affect how the pinion angle will stay while going though the suspension cycle. Two inches is not much at all. How do you think 6 to 9inches of difference would do? Think the angle would stay in check?
We both have high pinion RJ60s and I assume a CV driveshaft. I set my center limit strap at 4 inches of droop.

A lot of people don't run a center limiting strap; with 16 inch travel shocks and the flex capabilities that this 3-link has, I wouldn't be without one. I have witnessed a lot of trail carnage with 10-12 inch of unload over a ledge.

I hate the cliche' but I consider myself a bit old school. I tend to think about it while I am welding it. Then change it if it doesn't work in the real world.

39 inches is a lot of lower link, probably more than a fully skinned 4-door is going to exercise.

Possible go with whatever upper 3-link length you can get, then tack on the lowers and cycle the suspension. You can always shorten the lower links before you finish it up. I would pay more attention to the frame side upper/low link separation myself, but you are pretty much boxed in by the design of the JK on that based upon where you have to stick that upper frame side center link.
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post #7 of 18 Old 12-23-2011, 11:45 AM
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Quote:
Originally Posted by cjcraig7 View Post
We both have high pinion RJ60s and I assume a CV driveshaft. I set my center limit strap at 4 inches of droop.

A lot of people don't run a center limiting strap; with 16 inch travel shocks and the flex capabilities that this 3-link has, I wouldn't be without one. I have witnessed a lot of trail carnage with 10-12 inch of unload over a ledge.

I hate the cliche' but I consider myself a bit old school. I tend to think about it while I am welding it. Then change it if it doesn't work in the real world.

39 inches is a lot of lower link, probably more than a fully skinned 4-door is going to exercise.

Possible go with whatever upper 3-link length you can get, then tack on the lowers and cycle the suspension. You can always shorten the lower links before you finish it up. I would pay more attention to the frame side upper/low link separation myself, but you are pretty much boxed in by the design of the JK on that based upon where you have to stick that upper frame side center link.
That is some good advice!

70% would be the mininum we would recommend. Check out the seperate between the two and remember the operating angles will be different between the upper arm and lower arms so cycling the suspension to see what happens to the pinion angle and instant centers is important!

RK
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post #8 of 18 Old 12-23-2011, 12:00 PM Thread Starter
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Quote:
Originally Posted by cjcraig7 View Post
We both have high pinion RJ60s and I assume a CV driveshaft. I set my center limit strap at 4 inches of droop.

A lot of people don't run a center limiting strap; with 16 inch travel shocks and the flex capabilities that this 3-link has, I wouldn't be without one. I have witnessed a lot of trail carnage with 10-12 inch of unload over a ledge.

I hate the cliche' but I consider myself a bit old school. I tend to think about it while I am welding it. Then change it if it doesn't work in the real world.

39 inches is a lot of lower link, probably more than a fully skinned 4-door is going to exercise.

Possible go with whatever upper 3-link length you can get, then tack on the lowers and cycle the suspension. You can always shorten the lower links before you finish it up. I would pay more attention to the frame side upper/low link separation myself, but you are pretty much boxed in by the design of the JK on that based upon where you have to stick that upper frame side center link.
Thanks for the help. The bridge is going to be here next week and hopefully the joints too so I'm trying to get everything ready. My upper measurements are more like guesstiments right now but I know they are with in inches. I'm making the upper mount for the middle link now. Going to make the upper as long as I can like u said. I still need to make the mount on the axle bridge but not sure on how tall till I get the bridge welded on the axle. I know I need to try and keep the upper and lowers parallel as much as I can. I 'm new to this stuff so I'm kinda learning as I go. Once I get her all back together I will post up some pic's.

Either 12 or 14" travel RRD shocks are going on the rear. I will probably need limit straps to run the 14s but I wouldn't have a problem doing that.

Last edited by frankie945; 12-23-2011 at 12:13 PM.
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post #9 of 18 Old 12-27-2011, 05:57 PM
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I put that upper bridge joint right on top of the hat. The 9/16 mounting hole is 2 1/2" up.
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post #10 of 18 Old 12-28-2011, 08:02 AM Thread Starter
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Quote:
Originally Posted by cjcraig7 View Post
I put that upper bridge joint right on top of the hat. The 9/16 mounting hole is 2 1/2" up.
Thanks, I was looking close at your build how you trussed that bracket up looks really good. I will be watching your build on the front. Sounds interesting what you are doing with it.

I'm heading to work on that upper bracket now. I'll go 2.5 up for the hole than another inch up for anti squat adjustment. Was hoping to have this done by the weekend but seems it takes over 3 weeks to get 4 RK joints shipped to me. :-(
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post #11 of 18 Old 01-01-2012, 05:42 PM Thread Starter
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Update

I worked hard on this all day today by myself. I'm really happy how it has turned out. Thanks for the help cjcraig7 and Rock Krawler.

Here is how it started out a week ago

[IMG][/IMG]

Tapping is a pain in the butt.

[IMG][/IMG]

Welded on the bushing from poly performance. Had to turn down the 1.75 to 1.5 on the bushing end so I could get more to weld too.

[IMG][/IMG]

The RK joints arrived friday afternoon. Thank you RK!

[IMG][/IMG]

Ran out of 1/4 so I had to use 1/2 for the upper bracket on the bridge. It's not going anywhere. And I had trouble getting the first two bolts all the way tight on top of the bridge. Going to have to re tap them tomorrow.

[IMG][/IMG]
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post #12 of 18 Old 01-01-2012, 05:46 PM Thread Starter
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Upper frame link.

[IMG][/IMG]

1/4" bracket I made. Put it up high as I could.

[IMG][/IMG]

Flex pic's.. Need longer rear sway links and shocks there still off my old teraflex 2.5 kit.

[IMG][/IMG]

[IMG][/IMG]

[IMG][/IMG]

[IMG][/IMG]

Last edited by frankie945; 01-01-2012 at 07:35 PM.
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post #13 of 18 Old 01-01-2012, 05:55 PM
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Nice homebrew.

What poly joint did you use?
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post #14 of 18 Old 01-01-2012, 06:34 PM Thread Starter
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Quote:
Originally Posted by cjcraig7 View Post
Nice homebrew.

What poly joint did you use?
Thanks! Almost all of it was cut on a band saw. Wish I has a plasma.

Just used the ones in the builder section, think it was 18 bucks a piece. I feel no vibes at all and drives great! Less squat on take off now also. It was super quite when I was flexing it out. Should have bought the krawler flex joints though. I kinda screwed up making the lowers 1 inch too long so I don't have any adjustment to make them shorter, there threaded all the way in. In a few weeks I will probably order the better joints and fix my adjustment problem cause I want to move the axle forward 1/2'.

http://www.polyperformance.com/shop/...t-p-16605.html
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post #15 of 18 Old 01-02-2012, 03:23 PM
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The reason I asked you about the joint was I saw tape on joints in the picture. You did take the bushing out before burning them in...right. The tape was for paint?
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post #16 of 18 Old 01-02-2012, 04:36 PM Thread Starter
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Yes, I got the bushing kit. Pressed them with the press after welding them. They have a tapered edge on the end and were a bitch to press in.

Heck to make the upper link I couldn't get the solid round hot enough to bend. Torch was almost out of gas. So I cut it with the band saw to the mid way point heated it up in a vise and bent it. Then I filled it in with weld. Worked out good. Thing drives great on the street can't wait to get it off road now. Need new shocks. And then starting on building a front D60. Seems it will never end..
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post #17 of 18 Old 01-02-2012, 06:13 PM
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Wow, nice fab work. That baby flexes great!

08 2Door Red Rubicon. Rock Krawler 5.5 Longarm Coilover, Polly rear Coilovers. AEV hood & wheels, 37"KM2s, JE Reel 1350 shafts, 5.38 Yukon gears, Superior axles, Shrockworks stubby, Fab Fours rear, sPod, Rebel Offroad brakes, Warn winch and lots more.

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post #18 of 18 Old 01-03-2012, 07:52 AM
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No problem at all! Great work sir!

RK
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