Zr2 front suspension

GMCnewbie · May 25, 2025

1 minute ago, kylant said:

do you have a Chevy or GMC?

2024 GMC 2500 AT4

Chuck FB · May 25, 2025

18 minutes ago, GMCnewbie said:

2024 GMC 2500 AT4

I wonder if there is a difference in the height of the underside of the fender trim on a GM vs a Chev, with how random the factory sets the torsion bar height its hard to know and of course depends which factory tires one has or if measuring with factory tires at all and at what pressure, so many variables. Probably some way of figuring it out by measuring down to a certain spot on the frame for example.

GMCnewbie · May 25, 2025

6 minutes ago, Chuck FB said:

I wonder if there is a difference in the height of the underside of the fender trim on a GM vs a Chev

Great question. My guess is there's a difference and I say that simply because of the shape of the fenders between the Silverado and Sierra. But I have no clue. I shared my numbers simply to give folks an idea of what they might get from this type of swap. I was honestly surprised by how much lift my truck got. The front was initially higher (over 43") before I dialed it back a bit.

Not sure if I shared this already, but I went back and swapped my torsion keys again to the Cognito keys as the stock keys didn't give enough lift.

KvetL5P · May 25, 2025

16 minutes ago, GMCnewbie said:

Not sure if I shared this already, but I went back and swapped my torsion keys again to the Cognito keys as the stock keys didn't give enough lift.

Interesting, i'm going to be doing the suspension maxx keys with the zr2 swap.

kylant · May 25, 2025

13 hours ago, GMCnewbie said:

2024 GMC 2500 AT4

i have a '25. my measurements are nearly the same. still have to dial in final ride height.

I am pretty sure the chevy fender arch is higher than the gmc.

i had a little rattle coming from the passenger side. i could faintly hear it, but when i sat in the passenger seat, it was more noticeable. so i went back over all the bolts and checked torque. I found the lower shock bolt was loose even though I marked it as torqued . torqued it, and the rattle is gone.

revrnd · May 25, 2025

22 hours ago, GMCnewbie said:

The factory obviously didnt do a great job of dialing in the ride height of my truck as the driver side was 3/8" lower front and back.

I have no knowledge of the K2XX or T1XX assembly process but after the GMT400 model run, I saw no special fixture being used to set the Z height near the end of assembly. In the orginial Oshawa truck it was done on the 'flat top'/main line after the truck was pretty much complete & before initial start up.

I assume the other truck/SUV plants used the same tool. One of our tool makers made some revisions to improve durability & ease of use. Corporate showed some interest.

I havent looked under my truck @ the torsion adjusters or measured ride height.

Edited May 25, 2025 by revrnd

Chuck FB · May 25, 2025

33 minutes ago, kylant said:

i have a '25. my measurements are nearly the same. still have to dial in final ride height.

I am pretty sure the chevy fender arch is higher than the gmc.

i had a little rattle coming from the passenger side. i could faintly hear it, but when i sat in the passenger seat, it was more noticeable. so i went back over all the bolts and checked torque. I found the lower shock bolt was loose even though I marked it as torqued . torqued it, and the rattle is gone.

Speaking of suspension hardware torques as certain components would be more prone to needing a follow up re-torque after some use such as the rear leaf spring ubolts for example, GM's method of torquing the ubolts to 74 lb ft and then an additional 180 degrees of rotation doesn't work well with doing a typical bolt torque check because by their metric that would suggest loosening the ubolts to re-torque to 74 and then doing the 180 degree turn. I highly doubt most shops including spring shops would mess with that whole ordeal but instead have as is stated for ubolts that a spring shop makes up, each thread size has a standard torque value and that is that. So the other day I thought I would see what they felt like for torque on my truck with the little bit of use its had and crept up on my torque wrench setting to see about where it would start turning and seemed to be around 100 or less lb ft which for that size/diameter ubolt is certainly well under what it could be in my estimation anyway. As I noted those factory ubolts have formed/rolled threads so the threads are larger in diameter than the stock material but the material is 5/8 which is a pretty hefty size which they should be for an HD truck. I did torque mine up more in steps to a number I won't list but was very conservative based on bolt or ubolt charts, based on size and thread size and pitch. I've seen comments about the GM pickups having sounds coming from the spring packs after some use of the vehicle and I believe GM themselves saying the corrective action or one of them was to re-torque the hardware which totally makes sense as its no different on highway tractors etc, they have an initial stretch and settling period as its clamping a series of parts together and have to retighten them after being in service a while.

Chuck FB · May 27, 2025

I thought this might be interesting for those doing the lifts and he also noted a certain measurement distance which is from the underside and in this case the actual GMC brand fender to the center of the hub and I've mentioned this measurement tactic before simply because it eliminates anything to do with the wheel/tire diameter and zeros in on the actual height of the suspension front or rear for comparison purposes from one truck to the next. That was mentioned early on in the video. Yes the total height from the fender to the ground is very relevant as well as that gives the total suspension and tire package height as a whole for the finished product. He also made a comment about the wheel size and back spacing and although he did not mention what that wheels offset was it sounded to me like a certain amount of positive offset by the numbers he threw out. Certainly another company to pick their brain about lifts and wheel and tire combo's they run and its talking to the horses mouth as per the actual lift company rather than someone merely flogging their install shop.

GMCnewbie · May 27, 2025

Cool video with good information. I'm not a fan of cutting the bumper if at all possible. That's why I'm blowing more money on a bumper extender (set of washers basically) to give a little extra space for the new tires. I really liked how they addressed the front "mud flaps" by heating them and pressing them back a bit. Much nicer look than removing or cutting them.

Chuck FB · May 27, 2025

7 minutes ago, GMCnewbie said:

Cool video with good information. I'm not a fan of cutting the bumper if at all possible. That's why I'm blowing more money on a bumper extender (set of washers basically) to give a little extra space for the new tires. I really liked how they addressed the front "mud flaps" by heating them and pressing them back a bit. Much nicer look than removing or cutting them.

I agree that if one is wanting to do a certain modification such as the lift in this case and install larger tires, trying to accomplish it within a perameter of not doing permanent damage to the truck ( that I presume is your goal ), one needs to know all the parts and tricks to make that happen. Unfortunately the outfit you bought the wheels from probably didn't know what they were talking about and that is showing up now with that wider arc of tire movement as you steer so the tire is able to reach further forward and rearward then it would have with a factory offset wheel. I watched another video they did fairly lately of a truck they put an 8" lift on and 38" tires, well that got into trimming the bumper and cutting part of the rear structure of the lower fender ( front of cab ) and removing the mud flap all together to cram a tire that large into the wheel well so that really gets into a permanent butcher job.

GMCnewbie · May 27, 2025

Yup, trying to avoid "permanent" changes to the truck wherever possible. Everything I've done so far can be "easily" swapped back to stock if the next owner wants. I'm not switching back as I love the look and ride quality of the new setup.

kylant · June 22, 2025

Rear Spring Unit Bolt Nut[4x]: First Pass: 74 lb ft, Second Pass: Loosen 270degrees, Third Pass: 74 lb ft, Final Pass: 175 - 185degrees

are these really the torque specs for the stock u-bolts? this seems low

Chuck FB · June 22, 2025

2 minutes ago, kylant said:

Rear Spring Unit Bolt Nut[4x]: First Pass: 74 lb ft, Second Pass: Loosen 270degrees, Third Pass: 74 lb ft, Final Pass: 175 - 185degrees

are these really the torque specs for the stock u-bolts? this seems low

That's what is being said, I have no shop manual to confirm but also I never tried backing off a set of these ubolts so that I could then torque to 74, and then turn the additional 180 degrees and try to figure out what actual torque is being applied to the ubolts. It is a course thread which appears to be about 10 threads per inch in imperial measurement terms so a half turn would certainly do something in ramping up the ultimate torque value but to what, good question. Consulting a typical ubolt chart doesn't do much good either as the thread pitch is nothing like what a spring shop would handle, I can't be sure if its a grade 5 or grade 8 although in theory its probably along the order of a grade 8 as that is the common material used in spring shops I believe but only GM knows what the spec is. Is it considered plated threads or non plated, dry or lubed. There are so many more questions then answers. If only they would just give a normal torque value but no, can't make it easy.

The closest chart I find is a bolt chart using a grade 8 bolt that is 5/8 thread with an 11 pitch ( course thread ) and they specify 160 lubed and 210 dry threads. I just know that the non threaded material of these ubolts measures 5/8 but the threads are larger in diameter due to being rolled threads.

I can almost hear what a spring shop would say if I went to my local shop to see what they would torque a factory GM ubolt to, that they don't know because they throw them away and make up their own and use the ubolt torque chart ... that's my guess !.

If anyone wants to go through the pains of taking a near new truck with clean non rusty threads and loosen them off and then use the torque method GM says and then use a beam scale torque wrench to see what it reads when the nut begins to move, list your findings here !.

GMCnewbie · June 22, 2025

2 hours ago, kylant said:

are these really the torque specs for the stock u-bolts? this seems low

Damn! I had these on my list of torque specs and didn't even catch this one. I totally looked past this as it called out the rear spring "unit bolt" rather than u-bolt. Oh well. I googled the torque spec for the u-bolts on the 2024 GMC 2500 u-bolts and the AI response said 110lb ft along with a number of search results. I went with 110. I don't think I damaged anything as I did a check of the stock bolts on both sides before I removed them. Both sides appeared to be tightened to roughly 110lb ft based on my torque wrench. This is by no means scientific, but it was what I had available when I was working in my truck.

Edit: forgot to add I switched to the 3500 u-bolts due to the spacer added for the AT4X setup.

Edited June 22, 2025 by GMCnewbie