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ZR2/AT4X Part Numbers & Conversion Info

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Since the introduction of the ZR2 HD, many of us have waited for the parts to start hitting the market. They are now rolling out so let's build a thread where we can compile all the info on part numbers and related notes about converting a Z85 (standard) or Z71/X31 suspension over to the 1.5" lifted ZR2/AT4X.


First some press release links to the uninitiated:


ZR2/Bison - AT4X/AEV Edition


Long story short, the ZR2/AT4X has a factory 1.5" lift, extra underbody protection, and special dampers. The 1.5" lift is desirable because of the way it goes about gaining the extra height. Unlike aftermarket systems that use different torsion keys or attempt to ease up on the ball joint angle with a different upper control arm; GM uses a new upper control arm, lower control arm, steering knuckle and differential drop strategy. This allows for the 1.5" lift to maintain proper factory spec ball joint and CV axle angles without compromising ride or capability.


A few notes:

-So far it seems these parts will work on both gas (L8T) and diesel (L5P) powered HDs. At this time only the Multimatic DSSV shocks have unique gas/diesel/Bison/AEV Edition specs.

-The pricey Multimatic DSSV shocks are not required to run this 1.5" factory lift. Only proper shock height of an aftermarket shock will be required. For example the popular Bilstein B8 5100 is advertised for vehicles with 0-2" of lift.

-If you are looking for more of a leveled look, skip the rear lift blocks and leave the back of your truck stock. Going up 1.5" in the front should level out most factory HDs from a visual perspective.

-So far the complete part change list is UCAs, LCAs, Knuckles, Diff Drop Brackets, and Shocks for the front. Lift blocks, U-bolts (same as 3500 HD), Jounce Bumper Extension and Shocks for the rear. A one piece Front Skid Plate, Underbody Skid Plate (need confirmation on placement) and Transfer Case Skid Plate round it out. Bison/AEV Edition include unique part number Shocks and unique stamped steel Skid Plates (that at this time are extremely expensive).

-RPO for ZR2 is ZRX

-RPO for Bison is ULV


Part numbers:



Upper Control Arms:

Driver : 85144988

Passenger: 85144989

Lower Control Arms:

Driver: 85144990

Passenger: 85144991


Driver: 85144996

Passenger: 85144997

Differential Bracket:

Driver: 86787383

Passenger: 86787384

Mutltimatic DSSV Shocks (non-Bison/AEV Edition):

Front Driver: 86557795 (Unknown if Gas or Diesel only)

Front Passenger: 86557796 (Unknown if Gas or Diesel only)

Bison: Unknown



Lift Block x 2: 87844916

U-Bolt (same as 3500HD) x 2: 11610959

Jounce Bumper Extension x 2: 85565250

Mutltimatic DSSV Shocks (non-Bison/AEV Edition)

Gas x2: 86557751

Diesel x 2: 86557750


ZR2 Skid Plates (need confirmation whether AT4X is the same):

*Possible Front Skid Awaiting Confirmation* Underbody (need more placement details on where this is on truck): 85637479

Transfer Case: 85569359 (may need additional holes drilled in aft crossmember. Need more details)


Bison Skid Plates (need confirmation whether AEV Edition is the same):

Steering Rack: 85550010

Underbody (need more placement details on where this is on truck): 85550011

Transfer Case Skid Plate: 86513097


More info to come as it becomes available. Thanks to those on this forum that have done a lot of the leg work on this already @Joe97281 & @newdude


Edited by Epsilon Plus
Information adding/correcting.
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Thank you for this post!! I'm trying to determine if the DSSV shocks 86557795/86557750 will work on my 2020 Denali 2500 with stock suspension. Would a leveling kit with UCAs work? I don't want any more lift than necessary. 


I just got off the phone with a dealer and they show the rear shocks as not available so I'm hoping they just haven't landed yet. 


Appreciate whatever guidance you can provide!

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Any info on the electronic locking rear diff components and compatibility? That would be a mod I’d be interested in doing. 

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  • 3 months later...
Posted (edited)

I wish I could edit the original post as planned, but apparently that option times out. That said, here is some relative follow-up information from the larger discovery thread. This thread can serve as more of an up to date quick reference without digging through the minutia.


- This conversion works on both gas and diesel and has been successfully completed using all factory 2024 ZR2 parts on 20-23 trucks. GMC owners should substitute verbiage where necessary. X31 = Z71 and AT4X = ZR2 and AEV Edition = Bison. The swap mules on this site were Silverado but all of this will work with Sierra.


- At this time DSSV front shock usage will require modifying the hard and possibly soft brake lines on 20-23 trucks to accommodate the very large shock bodies of the DSSV. 2024+ non-ZR2s may not have this issue but no confirmations at this time. The preferred shock usage with this conversion is Bilstein B8 5100s as the standard versions of them allow for stock to 2" extra lift and are a perfect size fit for this 1.5" factory lift. Alternative to DSSVs if you want something in that quality/performance range try King remote reservoir shocks. At least they are rebuildable compared to DSSV and are of similar price range and arguably superior quality.


-85637479 is the confirmed front one piece ZR2 skid plate that replaces the plastic steering guard of all 4x4 trucks and the metal front diff skid of Z71 trucks. No extra bolts are required unless going from a non-Z71. The skid plate will be necessary to purchase when doing the full conversion as it allows room for the 1.5" differential drop. The stock Z71 skid will hit the diff if re-used. Non-Z71 trucks will have the bolt holes drilled and tapped already there waiting for the skid.


-The ZR2 transfer case skid is a partial direct fit. It will use (2) of the (3) bolts of the Z71 shield. If you are going from a regular 4x4 (non-Z71), you will need (2) 11518341 bolts (M10X1.5X25). The crossmember for the front skid holes will be drilled and tapped waiting for the skid. The rear of the skid will line up with the rear crossmember but you will need to drill and tap for (2) more of the same bolts, or alternatively like I did, drill through and use a through-bolt/nut/washer combo. I used a 3/8 stainless bolt with double washer and a lock nut. 2024+s may have the rear crossmember drilled/tapped for the ZR2 skid but need confirmation.


-The only item not reused on the swap is (1) of the (2) small 10mm bolts that help hold the brake hose bracket on the knuckle for each side. This sounds critical but the bracket holds on to the knuckle just fine in the stock divots and using the singular 10mm bolt. You can ziptie or figure out a way to secure the un-used top hole but the ZR2 knuckle is not drilled and tapped for it's usage in that spot. Use Loctite blue (low strength for future removal)  on the singular 10mm bolt if worried.


-There is two un-used bolt holes drilled and tapped on the UCA. These are for the routing of the 2024 brake lines that allow room for the DSSV. If you are converting a 2024+ over to ZR2 suspension, you may end up using these with your stock stuff and the above brake bracket bolt usage bullet point may not apply.


-ZR2s run LT305/70R18 (34.8x12R18) stock. Numerous ZR2 owners have converted over to 37s without trouble. This will largely depend on your wheel offset. I'm using a GM 18x8 with admittedly unknown offset, I am running Nitto 37x12.5s (36.5 actual height) with very limited rub on the front wheel liner. I've trimmed a small lower section of the liner and no longer have rub there. I have a touch of rub on the sway or frame at full articulation and turn lock but nothing audible, dangerous, or impactful long term. Those with custom wheel offsets that push the wheel out a touch should have no issues. Right now I'm sitting at 43 5/8" from ground to bottom of upper fender lip and about 44.5 in the rear using the full front/rear swap. I have not dialed it in all the way yet with the keys...etc until after I add the steering stabilizer (good idea when using 37s).


-Someone asked about using the e-Locker. This is likely a cost ineffective or impossible swap considering it is most likely tied into the BCM, ECM, and various other 4x4 modules. Just be happy with the good 'ol G80 that comes standard on all HDs. As far as fitting a unit in and somehow actuating it with something like a factory Aux switch? Well....get to experimenting.


I'll try to add more info as I learn it.

Edited by Epsilon Plus
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Posted (edited)

Relevant torque specs:


Front Lower Control Arm Ball Stud Nut: First Pass 37 lb ft, Final Pass 90 -100 degrees 


Front Lower Control Arm Nut [2x] First Pass 133 lb ft, Final Pass 45 -75 degrees


Front Lower Control Arm Bolt [2x] is torque to yield (single use) part number:  11549229


Front Shock Absorber Nut (top) [2x]: 48 lb ft


Front Shock Absorber Bolt: 118 lb ft


Front Stabilizer Shaft Bolt [4x]: 37 lb ft


Front Stabilizer Shaft Link (end links) Nut [2x]: 74 lb ft


Torsion Bar Support Bolt [2x]: 92 lb ft


Front Upper Control Arm Nut [2x]: 192 lb ft


Front Upper Control Arm Ball Stud Nut:  First Pass: 37 lb ft, Final Pass: 90–110 degrees


Front Wheel Hub Bolt [4x]: 133 lb ft


Front Wheel Hub Extension Nut [8x] 96 lb ft


Front Wheel Drive Shaft Nut:

First Pass: 244 lb ft, Second Pass: Loosen 45 degrees, Final Pass: 199 lb ft


Front Wheel Drive Shaft Nut is torque to yield (single use) part number: 11612295


Front Differential Carrier Bolt (Go from the top down on driver side): 81 lb ft


Front Differential Carrier Bracket Bolt [4x] (bolts that go from the bottom up on both sides through the large bracket openings): 118 lb ft


Front Differential Carrier Bracket Nut [2x] (bottom up, pass side): 74 lb ft


Front Differential Carrier Bolt[2x] (smaller bolts, bottom up driver side): 81 lb ft


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


Rear Shock Absorber Bolt -Upper: 70 lb ft


Rear Shock Absorber Bolt -Lower: 118 lb ft


Edited by Epsilon Plus
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Wow, lots of great info!

Checked a bit more into this and didn't find any issues with running a factory 20-22" wheel with this conversion.


Ordered most parts today including the skid plate.

Current plate sits right up against the diff so needs more space, just as you mentioned. 


Front sits right at 41" w/35x12.50-on stock 20's which are actually 34.5" and keys are cranked up a good ways at this point.  

Any indication of what dealers make of this conversion when it comes time for warranty work? 


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Posted (edited)

Wheel diameter won't be an issue, it will depend on tire width and wheel offset. Stock GM stuff should work fine and may only need minor fender liner trim.


This is the small amount I cut to alleviate the light rub on mine.





As far as dealer warranty it will depend on the service tech and whether they even notice. All the parts are GM stamped and painted black. No fancy looking aftermarket stuff....etc. On 35s they may just think you cranked the keys. If they were to measure or dig into the PNs they would figure it out or a very trained eye could tell a 24 ZR2 UCA from a 20-23 from the unused top holes for the brakes but most techs are just regular mechanics and not GM shade tree super fans like me. Officially, they have grounds to void steering and suspension warranty because of the numerous changes from stock. I'd rather not have Joey Bagadonuts service tech touching my truck anyway, so it matters not for me but for those concerned with warranty, default to a denial in your mind when modifying to this extent. 



Edited by Epsilon Plus
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