Zr2 front suspension

KvetL5P · March 18, 2025

4 hours ago, Epsilon Plus said:

The u-bolts wouldn't but the block just sits under the lowest leaf between the leaf and the axle perch. Would prob just need to source longer u-bolts from somewhere. I can measure my block if you need to know exact lift. If the 3500s are already 1.5" taller in the rear from the different spring packs, then it's a wash anyway.

Rear ZR2 lift is only needed for those who want the stock rake or just to say they have the full lift. Those just looking for the factory "level" can leave the rear stuff out.

Good to know! I didn't realize that the larger springs made the 3500s higher in the rear. Did you have to do any other mods to run 37x12.5s?

Chuck FB · March 18, 2025

35 minutes ago, KvetL5P said:

Good to know! I didn't realize that the larger springs made the 3500s higher in the rear. Did you have to do any other mods to run 37x12.5s?

While admittedly I haven't physically measured the main leaf spring pack thickness in my 3500 to compare with the 2500, what I did notice is that the length of the bottom overload leaf is shorter on the 3500 which is interesting. But as to the rear of a 3500 sitting up higher by eye vs a 2500, I would have to say no.

The reason a 3500 has longer ubolts is that the upper overload pack that sits on top of the main pack adds height to the over all spring pack and therefore requires longer ubolts to strap that all down to the axle housing, but the thickness of those upper overload springs don't affect the empty ride height. It would have to be a spacer block "under" the main leaf pack that sits on the axles spring pad "perch" that would add ride height. I haven't measured how much thread is sticking below the ubolt nuts but its probably not enough for much of a spacer block before running out of length. I've had numerous ubolts made over the years from pickups to highway tractors at a spring shop and they just need to have the proper length of rod that is pre threaded stock on each end ( and the correct diameter ) and know the profile of the bend and inner width of the bend they will have to make. typically on more popular suspensions they will have the information in their system and just require to know how long to make the ubolts Also its very common that the thread pitch of the rod material they have has a finer thread than a factory ubolt so new special deep nuts nuts will be required which the spring shops have in stock as well as the thick hardened washers to slip onto the ubolts for the nuts to go against if required. Not sure if any of this is of help ... oh and more than likely a spring shops ubolt material is not going to have some fancy gold or silver colored plating on it, just basic raw steel and if desired it can be degreased and painted before installing. No doubt the "fancy" custom ubolts from a lift company that are plated have a nice price attached.

kylant · March 18, 2025

i am pretty certain the rear height is the same 2500 vs 3500. the top overload spring makes the 3500 a 3500. it doesn't add any height to the pack. the main leafs appear to be the same thickness.

i have had several sets of u-bolts make a spring shop. they are generally $25 each. super easy to have them do it

Chuck FB · March 18, 2025

11 hours ago, kylant said:

i am pretty certain the rear height is the same 2500 vs 3500. the top overload spring makes the 3500 a 3500. it doesn't add any height to the pack. the main leafs appear to be the same thickness.

i have had several sets of u-bolts make a spring shop. they are generally $25 each. super easy to have them do it

I do find it odd why they felt the main pack bottom overload leaf needed to be different between the 2500 and 3500, there obviously is some reason to them designing it that way though.

kylant · March 22, 2025

for those of you who have made the swap, how is the ride without the DSSV shocks?
i am after the best ride possible.

my plan was to do the swap and run a set of Cognito comfort ride torsion bars. however, cognito says those bars won't work with the at4x/zr2 suspension.

so wondering if a traditional level kit with those bars or the factory "level" would give a better ride ??

GMCnewbie · March 22, 2025

2 hours ago, kylant said:

my plan was to do the swap and run a set of Cognito comfort ride torsion bars. however, cognito says those bars won't work with the at4x/zr2 suspension.

This is not completely true. I spoke with someone a few weeks ago when I ordered my comfort ride torsion bars and leaf springs. They said the bars will work, but it requires you to purchase new torsion keys. It would be great if they mentioned that on their site. The SKU for the Cognito keys is 110-90771.

I plan to start the install process tomorrow morning for my swap. I went with the Fox 2.5 HTO shocks for my truck. No clue how good they are. I had the Fox 2.0 shocks on my Power Wagon and liked them. The advertising claims the 2.5 HTOs offer more control for these trucks. We'll see how it goes.

Edited March 22, 2025 by GMCnewbie

kylant · March 22, 2025

9 hours ago, GMCnewbie said:

This is not completely true. I spoke with someone a few weeks ago when I ordered my comfort ride torsion bars and leaf springs. They said the bars will work, but it requires you to purchase new torsion keys. It would be great if they mentioned that on their site. The SKU for the Cognito keys is 110-90771.

I plan to start the install process tomorrow morning for my swap. I went with the Fox 2.5 HTO shocks for my truck. No clue how good they are. I had the Fox 2.0 shocks on my Power Wagon and liked them. The advertising claims the 2.5 HTOs offer more control for these trucks. We'll see how it goes.

hey. thanks for that info. so their leveling keys just need to be bought? that makes sense. I imagine the bars on the x/2 are just cranked and there is no more room to crank with the stock keys.

throw in a lighter bar that needs to be cranked more, there would not be any room. add a reindexed key and there will be adjustment.

one person also said the comfort ride full leafs and the mini-pack leafs have about the same ride quality. don't really see how that is possible??

i guess it all depends on who you talk to there...

GMCnewbie · March 26, 2025

On 3/22/2025 at 7:38 AM, kylant said:

i guess it all depends on who you talk to there...

That's absolutely correct. I have zero experience with butt-in-seat with either the comfort ride leafs or mini-packs. I chose the comfort ride leafs as it wouldn't require me to take apart the leaf pack. I'm just replacing the entire setup. Much easier in my mind.

I've spent the last 4 days under and around my truck working on the complete suspension swap. This project is not for the faint of heart for sure. I've done a suspension swap on my wife's Expedition 2 years ago and assumed this would probably be a little more difficult because of the leafs and torsion bars. Man was I wildly off the mark on that assessment. This has been a beast. That said, it's not the worst job in the world assuming you're technically capable and have all the right tools readily available. I have completed the majority of the work, but I'm waiting on Fox to ship me mounting bolts for my new shocks (they failed to include them in the boxes). So the front end is just waiting on those bolts, which should be here tomorrow, and I'll be able to wrap that up. I'm also waiting on the leaf spacer as I somehow forgot to add that to my order back in Oct. So for now I've installed the new shocks in the back and will do the leafs and other parts in the rear in another week or so when the parts arrive.

I will share what I consider helpful tips and tricks in the next few days. I'm mentally beat at the moment and want to get the shocks installed and the truck running before making the list. My hope is these items will help the job go a little easier for anyone else considering this project. There's been a lot of trial and error for me on this one as I've never owned a truck with torsion bars or leafs before.

OS RR · March 26, 2025

Experiences like that are why I lean towards Cognitos "standard" kit with tubular arms (along with Bilstein shocks, and SuperSteers steering kit). I've already confirmed with them that it works from stock to 3". I'm only looking for ~1.5" to mimic a Z.

I understand what it takes to rip the suspension out. Just not sure I wanna do it in my drive way. Loosening the T bars and swapping Uppers seems much easier.

Edited March 26, 2025 by OS RR

kylant · March 26, 2025

i have done suspensions on nearly all my trucks. i am pretty proficient at it. the last full IFS kit i have done was years ago though. that involved cutting, etc...

this swap doesn't appear like it would be too difficult. i am looking forward to the final thoughts and review.

i honestly feel swapping the mini-pack would be easier than the full leafs on these trucks. supposedly the whole hitch needs to be removed the swap the leafs

GMCnewbie · March 26, 2025

28 minutes ago, kylant said:

i honestly feel swapping the mini-pack would be easier than the full leafs on these trucks. supposedly the whole hitch needs to be removed the swap the leafs

I've seen that comment as well about ripping out the hitch. I was under the truck on Sat and didn't get the sense that I needed to go that far with it. You do have to remove the spare tire though to get to one of the shackle bolts. I'm hoping that's all I need to do. Regardless, I'm in for whatever's needed at this point. I just want to get it done. lol

1 hour ago, OS RR said:

Experiences like that are why I lean towards Cognitos "standard" kit with tubular arms (along with Bilstein shocks, and SuperSteers steering kit).

You're not wrong with that line of logic. I chose not to go with the aftermarket lift specifically because of the geometry involved with the steering and axles. I've read that just doing the UCAs with lifts has a greater potential for causing issues down the road with failures in those areas. Again, I don't have first hand experience to speak to that, but the comments I read spooked me enough to go the full swap route instead. At the end of the day it's your truck right. They're selling a ton of kits. I can't image they're terrible or anything. I honestly only wanted a minimal lift to clear larger tires. I'd love to go with a 3-4" lift, but my wife is 5' tall and struggles getting in and out as it is. lol

GMCnewbie · March 26, 2025

The other thing I'll add quickly to this is that I did all the work by myself. My son helped for a few hours one day grabbing tools and drinks for me, but I did all the heavy lifting. I wish I had an extra set of hands and another set of eyes on this. That would've helped make this job a lot easier as the parts are not light at all. And I struggled with removing a few pieces because I wasn't looking at something in the right light. I eventually got to the right place, but I had to step away and reset to get there.

Edited March 26, 2025 by GMCnewbie

OS RR · March 27, 2025

2 hours ago, GMCnewbie said:

You're not wrong with that line of logic. I chose not to go with the aftermarket lift specifically because of the geometry involved with the steering and axles. I've read that just doing the UCAs with lifts has a greater potential for causing issues down the road with failures in those areas.

I'm guessing GM came to the same conclusion but probably because of warranty purposes.

kylant · March 28, 2025

GMCnewbie,

do you think the diff drop brackets can be used without the new knuckles and lower control arms?

basically use them with an aftermarket leveling kit?

thanks

GMCnewbie · March 28, 2025

7 minutes ago, kylant said:

do you think the diff drop brackets can be used without the new knuckles and lower control arms?

basically use them with an aftermarket leveling kit?

I would guess so. I don't believe the diff carrier brackets give much of a drop from what I could tell holding the bars next to each other. Someone else here might have better details on the true differences between the two brackets as I was exhausted by the time I got to the carrier brackets.