Rear flex...help...and stuff...

[FJBen]

I'm not overly impressed with most linked suspensions people just piece together. You really have to do your research and get all the geometry perfect to end up with something that works right. Most the time getting that link geometry right involves building the chassis around your suspension. I have wheeled with a lot of people that don't have their roll center high enough and there junk flops way too easy off camber. I have also wheeled with a lot of people that don't have their squat values even close to dialed and their pile hops like crazy, while my leafed rear end with proper setup on the wrap bar hooks with no hopping involved. One particular person had the proffits kit and the thing just didn't work, which is why i'm not a fan of prefabricated link geometry. Not trying to steer anyone away from getting their kit all the brackets and stuff is great but make the geometry work with your particular truck, COG wheelbase, that sort of stuff.

I would not use 80 parts all those links are way too short to start with, your roll center and anti-squat would suck…

thats the part Im' afraid of with the links. I'll get the number wrong and it will flop and wheel like crap...But in all honesty...it can't be *that* hard...I suppose if you model it "similar" to a heep rear, it should work well.

You really think the 80 rear would be all wrong??? There's a page that someone swapped the full suspenion (i wouldn't do the front) and it seems to be working real well on a 40.

I know the springs wouldn't work..but it's all basically geometry...plug it into the calculator and go correct? The lower links have to be close to 34" or in that range. if you used them top/bottom and did the geometry on the 4 link calcs....

I know the longer leaf springs would probably be the easiest. maybe using stock XJ rear springs, or dakota rears? But I don't really want to mess with flipping the rear/doing rear d-shafts right now...so that might screw me over.

Because even with the longer shackles...it still doesn't really flex for poo at the rear.

 

[bustanutley]

Building a 4link is a huge can of worms. I had a system designed and ready to rock for my 40, took me months of reading to understand all the terms, know how everything worked a gather what the true general consensus was for the type of numbers you should end up with for it to work with the type of terrain you intend to wheel on and just how you want your pile to work. The hardest and most important variable you need to have before you start is the COG of your truck in the z-axis. Lots of people use the location of the top bolt on the bellhousing, but that is just a guess and to do things right there is a procedure to quantify that number. Last year I went to Moab first time since my SOA; a place full of ledges and climbs where link suspensions are supposed to be king, and my rear end worked so well I can no longer justify changing it, at least for now. I just need to pony up for shocks, right now I’m running treeroot junk yard specials, every single one mismatched. My front however gets some wrap and I need to address that.

As far as the 80 parts, I’m sure you could make it work, but I guarantee it would work better with new parts that you aren’t stuck with certain parameters.

The problem you are occurring is a simple one: the springs front to rear are not the same distance from the centerline of the truck, while the springs are virtually identical (same length, same spring +/- a few leafs).
My suggestion to simply make the rear flex without changing anything is move the rear shackle mounts forward until you end up with a 45deg angle on your shackle, I guarantee that will make it work mo better.