Cognito 1" Block & 16" U-Bolt Kit | 2011-2026 Silverado/Sierra 2500HD/3500HD 2WD/4WD

The Obsidian Vision

On a 2011–2026 Silverado or Sierra 2500HD/3500HD, a 1-inch rear block and U-bolt kit is the foundational rear lift component that sets the rear ride height increment required to level the truck, accommodate longer rear shocks, or achieve the stance target of a complete front-and-rear lift system — and the quality of that block and U-bolt assembly determines whether the rear axle stays precisely located under tow load or shifts under the torque and lateral forces that a heavy-duty platform generates. The Cognito 1-Inch Block and 16-Inch U-Bolt Kit delivers that foundation with 1-inch cast steel blocks finished in semi-gloss black powder coat and heavy-duty zinc plated straight U-bolts sized at 16 inches for the GMT900 and T1 2500HD/3500HD rear axle — a USA-made assembly engineered to hold axle position precisely under the sustained loads of a Duramax diesel at maximum tow rating. At 1 inch of rear lift, this kit is the correct component for fine-tuning rear stance, accommodating longer rear shocks in leveling applications, or serving as the rear lift increment in a complete Cognito suspension system.

Concierge Fitment Guarantee

Every order is manually reviewed by our technicians to ensure 100% compatibility with your build before we ship.

Engineering Breakdown

• Lifts the rear of the 2011–2026 Silverado/Sierra 2500HD/3500HD exactly 1 inch via cast steel blocks positioned between the rear axle perch and the leaf spring pack, providing the precise ride height increment required for leveling, shock length accommodation, or complete suspension system rear lift without altering spring rate or leaf pack geometry.
• Secures the rear axle to the leaf spring pack under sustained tow loads and hard acceleration through heavy-duty zinc plated straight U-bolts sized at 16 inches for the GMT900 and T1 HD rear axle housing, preventing the axle shift and spring walk that result from undersized or corroded U-bolt hardware.
• Maintains rear axle alignment and pinion angle geometry at the 1-inch lift increment through the cast steel block's precision-machined seating surfaces, ensuring the axle remains centered and the driveline u-joint operating angles stay within specification at the new ride height.

Rear lift blocks function by repositioning the rear axle perch relative to the leaf spring pack — the block sits between the axle perch pad and the spring center bolt, raising the axle by the block's height while the U-bolts clamp the entire assembly together. The structural integrity of both the block and the U-bolts is critical: a block that deforms under tow load allows axle rotation (wrap), and a U-bolt that stretches or corrodes allows the axle to shift laterally under cornering and braking loads. Cognito's cast steel blocks are powder coated semi-gloss black for corrosion resistance and machined to consistent height tolerances that ensure even load distribution across both spring perch contact surfaces. The 16-inch zinc plated straight U-bolts are sized for the GMT900 and T1 2500HD/3500HD rear axle housing diameter and provide the clamping force required to maintain axle position under the high torque reaction loads generated by Duramax diesel powertrains at maximum tow rating. All components are manufactured in the USA.

Audit Table

Verified Fitment (OFAS Standard)

✅ CONFIRMED:
2011–2026 Chevrolet Silverado 2500HD 2WD/4WD
2011–2026 Chevrolet Silverado 3500HD 2WD/4WD SRW & DRW
2011–2026 GMC Sierra 2500HD 2WD/4WD
2011–2026 GMC Sierra 3500HD 2WD/4WD SRW & DRW

❌ REQUIREMENTS:
Requires rear pinion angle check post-installation — at 1 inch of rear lift, verify driveline u-joint operating angles remain within GM's specification before towing at rated capacity.
Requires U-bolt torque verification after the first 500 miles of use — U-bolts can relax slightly after initial load cycling and must be re-torqued to specification to maintain axle clamping force.
Requires rear alignment check if the vehicle is used for precision towing or if any lateral axle shift is suspected after installation.

Installation & Technical Notes

Estimated Install Time: 1–1.5 Hours DIY Install (with basic lift equipment, hand tools, and torque wrench)
Alignment Required: Pinion angle check recommended post-installation — verify driveline u-joint operating angles are within GM's specification at the 1-inch rear lift height.
Torque Specifications: Refer to Cognito's included instruction sheet for U-bolt torque values — torque in a cross pattern with the suspension at ride height under load. Re-torque after the first 500 miles.
Block Orientation: Verify block center pin alignment with the spring center bolt hole before torquing U-bolts — misalignment will cause axle shift under load.
Towing Note: After installation, verify rear ride height and pinion angle under full tow load before extended towing at rated capacity. U-bolt clamping force must be confirmed at operating load.

Wheel & Tire Fitment

This kit provides 1 inch of rear lift — wheel and tire fitment at this lift height is unchanged from factory on the 2011–2026 Silverado/Sierra 2500HD/3500HD platform. No additional fender clearance modifications are required for standard tire sizes at 1 inch of rear lift. For builds running 35-inch or larger tires, verify inner fender clearance at full compression with the new rear ride height before finalizing wheel and tire selection.

Our team is standing by to verify your specific rear axle configuration, tow setup, and lift system before we ship. Purchase with confidence; we review every build.