Rear Shackle Mods - Crash/Gearwhine Others?

I have been contemplating welding a similiar plate over my rear shackle box that I think both of you (and others) have already done. I hope to get rid of my blocks and add more articulation. I saw in the archives that I will get about 2" of lift, but how can I figure out exactly where to weld on the new hanger to get the maximum droop and compression out of the springs?

I figured I would:
1) measure the max. length of the springs by laying a string along the length of the spring from eye to eye
2) measure the length of the springs (eye to eye) under normal load.
3) measure the amount of uptravel to bumpstops
4) make a scale drawing to determine max length of springs in relation to the bumpstops limiting uptravel

Am I thinking too much? Is there something I am missing? What did you guys do to figure this out? Did you worry about it?

Thanks for the help, I hope to do this this weekend

I have leafs up front, so I had to figure out where I wanted to mount the shackle so I could get the best shackle angle. I used the same style shackle that an XJ/MJ uses in the rear, then welded 2 pieces of 1/4" plate with several holes in them. this way I could move the shackle's top end forward or backward if the springs sag or I find that it doesn't give enough compression or droop.

thats a good idea, does the 1/4 plate on each side interfere with the shackle at full compression? (stock style or 2" longer than stock shackle) I am unsure about a front end, but I think if I have two plates or brackets running the length of the plated factory shackle box, that hang ~ 1.0-1.25 inches down from the top plate that they may limit the rear swing of the shackle under full compression? I will have much more droop than compression, so at full compression I want my shackles to lay flat on the top plate to get max front swing & articulation. Thanks for the idea though, I may be able to just shorten the amount of rearward adjustment or length of the brackets, that will work.

Just add a couple holes so you can adjust. Then if you ever decide to change your shackle length you have the variability to tune in the rear suspension a bit more.

http://community.webshots.com/photo/64838123/70343261CHaGmc

Also, don't forget lowering that mount will tilt your pinion upward which could cause vibes depending on your setup. Maybe not, but it should be thought of either way.

just put the extra holes there, then when you figure out which one you want you can chop off the others if they're getting in the way.

i don't think you'll be able to set it up so that the shackle lays flat at compression. my understanding is the effective spring-rate increases as the shackle angle flattens.

I think you're really overthinking this, just set it up with the shackle at a 30-45 degree angle from verticle and I don't think you'll be disappointed.

I welded up my hanger to have about a 45* angle. But what I neglected completely when doing it was that I had no load. It bangs the frame all the time if I have some weight. I still haven't gotten to fixing it.

I say weld the hanger on very loosely, but enough to not break sitting in one place. Set the jeep down, and load your jeep to a decent amount but not too much. At static load try to get a 20-30* angle. That seems to be a decent angle to get max up and down travel. 45* is not great for compression, but great for droop.cut and reweld if it's off. It shouldn't take more than one cut and reweld after seeing what your initial set-up came to.

I take shackle angle as a guess and check thing, you're almost never going to get what you want first try. _nicko_

Thanks for the info! Driveline angle should not be a problem once I ditch the blocks for this mod. I think I am going to do the measuring explained in my first post to get in the ballpark, then fine tune later. Obviously though not THIS weekend. The outlaws dropped in for a weekend visit! So no jeepin for me.