Warning-Consider who's writing this-it is long...
From bone stock to current setup, and at various points temporarily in between, I've had a range of up travel from as little as 1.5" up to the current 6" up now. On down, I've had a range probably in the 3"-6" neighborhood if I had to guess. I know the up travel I've had because I've hated it at many points throughout the build for various reasons. With the new build, up travel was one of the most important things I wanted out of the new setup. It was a bit more difficult for me to accomplish due to lift height as I was not interested in lifting the rig any higher to get it. I run well used 3" springs so gaining max up travel was a bit of a job to make it work properly. I had been running right around 4" up at that time, and still hated it for my use. I was set on optimizing useable travel out of the setup which meant 12" shocks and due to very trusted friend's advice and advice of the custom shock tuner, I went with 50/50 travel for best performance. That meant 6" up and 6" down out of the 12" shocks, on my old 3" springs.
In order to make that happen, several issues came up along the way that needed addressed. On the surface and probably most glaring issue was shock mounts-front and rear both, you absolutely must have custom mounts to fit a shock this size. Mine are the same at all corners. I built custom out-board towers at both ends in order to fit them. My shocks have remote reservoirs and I honestly screwed up in the rear as I "overlooked" dealing with the shock's remote res tube. I had originally intended to run my reservoirs in front of the shock on top of the frame. I had stuffed my shock towers so high in the fender well though that it was impossible to fit the hose between tower and body. I clearanced a bit out of the fender but wasn't enough and should have just left well enough alone. This became an issue that I had created and had overlooked being my "first time" build of this nature. I ended up stuffing the reservoirs to the rear on top of the frame and behind my rear anti-rock arms. This type of error will not be possible on a TJ length rig or something with no stretch. I had JUST BARELY enough space to make this work after shifting things around and building custom angled mounts to support the reservoirs.
I suppose I should have prefaced with I wanted this to all work without cutting the tub and with running the factory fuel tank-no fuel cell for this build. I have a little girl who loves riding in the Jeep so back seat and rear storage is mandatory and would not be sacrificed for any reason.
The actual fitment of the shocks was relatively easy once towers were built. From there, there are many other changes that were necessary to gain the up travel with the new link design
In the rear, keeping factory gas tank and gaining most up travel possible, I had a number of issues to deal with. The factory gas tank was one of them. I have run stock, kilby skid with no BL, kilby skid with BL, Savvy skid with BL, and now my "modified" setup. In order to gain most up travel, I had to deal with the tank. This was fine as the tank was still an issue on my low slung LJ and I beat the hell out of it all the time. I wanted to raise it so this was just perfect timing. I ended up raising the tank even more than the Savvy skid allows for in highest position and pushed it back as far as I could with more mods. My Specific tank mods likely won't be necessary for maximum up travel on other rigs so I'll skip exactly what was done here as it is elsewhere in my build. With the tank relocated however, it was time to push the axle back and see what cleared and what didn't. I run a triangulated 4 link rear with link bridge/truss and 2.5" JJs mounted on top of that truss/link bridge. This meant running the truss as low to the diff as I could as the 2.5" JJs in the mounts require nearly 3" of clearance in their own right. Yes it's less than that, but still even after shaving the mounts and making things as tight as possible, it's still a large chunk of room to deal with to get 6" up with short springs. At full stuff, I ended up notching and modding one of the LJ tubs lower tub supports that run the width of the tub. This gained around or over 1/2" up at the top of the diff. Due to my lower arm triangulation and mounts on the axle, my arms came in contact with the frame at around 5" up relatively speaking. In my case, this meant cutting the frame and building an inner notch to allow the lower arms to stuff up literally inside the frame rails on the lowers at full bump, and boxing everything in for strength. Not visible from the outside of the rig, but underneath and inside, I've notched out a large section to allow for this at full stuff. With these mods in the rear, I was able to get a full 7" of up travel possible on the short springs yet I'm running 6" with the shocks and have a little room to spare for clearance without contact above everything.
With the rear done, the real fun was on the front. Again, I wanted 6" up at all corners and new towers done similar to the rear for ease of fitment and keeping everything the same. Shocks at all corners are the same, all arms/joints are the same, etc. The towers required clearancing the Metalcloak aluminum inner fenders and again, fitment of the reservoir and hose clearance. Lower shock placement was a bit different than the rear as you have the lower arm to deal with here-in the rear, it's on the other side of the tube and out of the way.
The front end was a chore to say the least. There is a LOT going on with steering up front, track bar to deal with, diff cover clearance, truss, etc., etc., etc. Obviously keeping the link bridge/truss as low profile as possible to the top of the diff as the 2.5" JJs take up a lot of room. I had been running an old JKS track bar and due to design of that bar, I was limited in up travel to around 4" I think? I forget exactly. It was well short of my intended goals so I had to go with the new style Currie TJJ track bar with bigger bolts. It's off set at the joint and bent slightly different which gained the clearance needed to get that extra 2" up. It's not that simple though-just having the bar wasn't enough. I still had to grind out part of the gusset on the bar and I cannot run the standard zerk fitting at the joint, I need a low-profile zerk to grease it. In addition, I had to grind out part of the factory track bar mount to gain clearance with the truss at full stuff. That's just for the track bar and relatively minimal to say the least in the big picture. The truss also needed heavy grinding to clear even with the other track bar changes. As we're on the topic of the truss itself, mine is a standard U shape over top of the diff and does NOT spread full width. It is for tight clearance due to limited space, hence my use of "link bridge" as it does that more than the job of a "truss" if you get picky. It provides the base for the upper link, primary job if that makes sense. This link bridge also required heavy grinding to clear the oil pan at full stuff and a re-shape was necessary to allow for that. It needed clearancing in many places front/rear/sides, etc. due to steering, engine, mount interference, etc. Don't forget that on the front, in order to get it low, you need to cut the factory diff housing and eliminate the factory upper bushing from the diff itself, then grind things out to make use for low profile mount. On top of the bridge is again, the 2.5" JJs so location of the upper joint was of critical importance as it won't fit "just anywhere" to gain max up travel on a low spring. Placement is critical to clear everything. Keep in mind I have full AC on my rig and was not willing to sacrifice any of my "creature comforts" as I have precious rear cargo who is wonderful at letting me know when something isn't right.
With the joint placement determined, I then had to follow that joint to the other end through the arm. The arm placement and location ended up making contact with my driver engine mount and restricting up travel by a fair amount there as well. I ended up having to notch and clearance both my factory engine mount and re-brace it as well as modify my Savvy UA front crossmember mount in order to clear and provide max up travel at the same time.
There was more to it than this even, but I'm at a loss right now what else was dealt with. Those are the big issues. This was strictly to deal with getting the up travel I wanted, and left out total suspension design, link design and placement, etc. Up travel issues only. I wouldn't call them "problems", just issues that need to be addressed if you want to run max 6" up on a low spring like I have. I was only able to provide about 6.5" total up here in front I think it was and am running it at 6" for the shock. If I was willing to run a standard 4" spring, I'd have a lot more room to work with and getting the up travel would not be near as much work. This was just what I dealt with on mine as it's still somewhat fresh in my mind. Yours will likely be different.
My thoughts now with 6" up is simply that it is Awesome! For the first time ever with this rig, I am very happy with it's performance. Up travel is only a small fraction of the total package, but it is SO much nicer and SO much better to have as much as I could get with this than anything prior. The rigs performance is so much better on all terrain from simply keeping planted on rough washboard to climbing obstacles in low range and having the ability of the tire to stuff further into the well before lifting the entire front end of the rig helps keep traction to the ground much better than before as well as a more stable rig and more enjoyable to drive. I was in the bumps a lot with 4" up and found the front end lifting more than necessary due to lack of up travel which limited traction and was a hinderance in certain situations. As of yet, I haven't hit the bumps on higher speed stuff and have thoroughly enjoyed having more up over slow crawl stuff as that 2" extra has proven to be a huge improvement in the technical stuff. Very hard to describe how and what is happening as well as the feeling driving, but it is thoroughly enjoyable to say the least.
I won't say gaining max up is "hard" to do, but it certainly isn't easy either and there is more to it than one might think on the surface. It is SO worth the work though and I very highly recommend taking the time to do it. I'm very pleased to say I'm "happy" with the suspension for the first time ever on my rig. I bought it new in '05 off the lot and this is the 4th and final revision. It's taken over 7 years-almost 8 to get this far but it has most certainly been worth it in the end.
Sorry for the length, I warned ya!
Hopefully that helps address a few of the issues I faced with my setup in order to gain max up travel on my low springs. Something to think about if nothing else.
Best of luck,