ReadyLIFT 2.25-Inch Cast Iron Rear Block Kit | Anti-Rotation Ears | Model-Specific E-Coated U-Bolts | Net 1" Gain on 2007–2024 Trucks | 1999–2024 Chevy Silverado / GMC Sierra 1500 6-Lug | SKU: 66-3002

Verified Fitment

Does NOT fit:

• GM 1500 trucks with composite rear overload springs — explicitly excluded per ReadyLIFT; the composite overload spring geometry is incompatible with this block
• 2019–2024 GM 1500 trucks with composite mono-leaf rear springs — mono-leaf springs use round/circular U-bolts at the top of the leaf spring; this kit requires traditional steel leaf springs with square U-bolts; see identification note below
• 8-lug GM trucks (Silverado/Sierra 2500HD / 3500HD) — different rear block geometry; this is a 6-lug 1500-series kit only
• Silverado 1500 Trail Boss and Sierra AT4 — these trims use different factory rear suspension configurations; verify before ordering
• 2WD trucks 2007–2024 with a factory rear block already installed at a height other than 1.25" — net lift calculation will differ; measure factory block before ordering

Mono-leaf spring identification — mandatory check on 2019–2024 trucks: GM introduced composite mono-leaf rear springs as an option on the 2019+ T1 Silverado/Sierra 1500. The mono-leaf is identifiable by the U-bolt shape at the top of the leaf spring — round/circular = mono-leaf = this kit does NOT fit. Square U-bolts = traditional steel leaf spring = this kit fits. Check under the rear of your truck before ordering.

Net lift math by generation:

• 1999–2006 (no factory block): install this 2.25" block → gain 2.25 inches
• 2007–2024 (factory 1.25" block): remove factory block, install this 2.25" block → net gain of 1.0 inch (2.25 - 1.25 = 1.00)

Component Specifications

Anti-rotation ears — why they matter: Without anti-rotation ears, a rear lift block can twist on the spring perch under hard braking, acceleration, or cornering — shifting the pinion angle and creating driveline vibration. Cast-in anti-rotation ears interlock with the spring perch geometry to prevent that rotation. This is the same design philosophy as the factory GM rear block that this kit replaces.

Shock length verification — do this before ordering: At 2.25 inches of block height (or 1.0 inch net on 2007–2024 trucks), the rear axle drops relative to the factory shock mount, increasing shock extension travel requirement. If the factory shocks are near full droop already, the added block height will fully extend or over-extend them — binding the shock, causing premature wear, or damaging the shock body. Measure factory shock droop travel before ordering. If insufficient droop travel exists, order the ReadyLIFT shock extension (67-3809) alongside this block kit.

Field 4 — What Is and Is NOT Included

Critical Compatibility

Two spring type checks — both must be confirmed on 2019–2024 trucks:

1. Composite overload springs: If your 1500 has composite rear overload springs (a stiffer secondary spring pack), this kit is not compatible. Composite overload springs attach differently than standard leaf spring packs, making this block kit's geometry incorrect for that application.
2. Mono-leaf composite springs: The round/circular U-bolt at the top of the spring identifies a composite mono-leaf application. Round U-bolt = do not order this kit. Square U-bolt = traditional leaf spring = this kit confirmed.

6-lug only — 1500 series. The GM 1500 series uses a 6-lug bolt pattern. The 2500HD and 3500HD use 8-lug patterns and completely different rear block geometry. If your Silverado or Sierra is an HD model, this kit does not apply.

2007+ truck owners — do not stack the factory block with this kit. Remove the factory 1.25" block entirely and replace it with this 2.25" block. Stacking may be illegal in some states and creates an unsafe load path that can cause block separation under heavy braking or load conditions.

Shock droop verification is not optional. The shock extension (67-3809) protects shocks from being over-extended at the new block height. Verify factory shock droop travel before installation day — having 67-3809 in hand if needed prevents a second order and installation delay.

Installation Notes

Skill level: Beginner to intermediate — bolt-on rear block installation. No cutting or welding required. ReadyLIFT recommends installation by a certified mechanic.

Tools required: Floor jack and rated stands, basic socket set, torque wrench. For 2019–2024 trucks: side cutters or grinder to trim excess U-bolt length after installation.

Pre-installation — verify shock droop: With the truck on a lift or on jack stands with the rear axle at full droop, measure the remaining shock travel. If insufficient travel exists for the new block height, order the ReadyLIFT 67-3809 shock extension before scheduling installation.

Installation sequence:

1. Safely lift and support the vehicle with the rear axle at full droop.
2. Remove the factory U-bolts and lower the rear axle.
3. Remove the factory rear block (2007–2024 trucks only) — do not leave factory block in place.
4. Position the ReadyLIFT 2.25" cast iron block between the axle perch and the leaf spring. Ensure the anti-rotation ears interlock correctly with the spring perch geometry.
5. Install the model-specific e-coated U-bolts and thread nuts with washers.
6. Lower the axle to ride height.
7. Torque U-bolts to OEM specification at ride height — do not torque with axle at full droop.
8. 2019–2024 trucks: Trim excess U-bolt length per ReadyLIFT installation instructions.

Post-installation mandatory steps:

1. Re-torque U-bolts after 500 miles — blocks settle slightly under initial load cycling.
2. Alignment verification — recommended after any rear height change.
3. Headlamp aim adjustment — required.
4. ADAS verification — check all safety systems.

Common Questions

How do I know if my 2019–2024 Silverado/Sierra has mono-leaf composite springs?
Look at the rear leaf spring where the U-bolt wraps around the top of the spring pack. If the U-bolt is round/circular in shape, you have mono-leaf composite springs — this kit does not fit. If the U-bolt is square-cornered, you have traditional steel leaf springs and this kit fits. This is a 30-second visual check from under the truck.

My truck is a 2007 Silverado 1500 — how much lift will I get?
Net 1.0 inch. The 2007+ GM 1500 came from the factory with a 1.25" rear block. When you remove the factory block and install this 2.25" block, the math is 2.25 - 1.25 = 1.00 inch of net additional rear lift.

My truck is a 2003 Silverado 1500 2WD — how much lift will I get?
2.25 inches. The 1999–2006 GM 1500 did not have a factory rear block installed. Installing this 2.25" block gives you the full 2.25 inches of rear lift.

Do I need the ReadyLIFT shock extension (67-3809)?
It depends on your current shock travel. The shock extension is listed by ReadyLIFT as a "may require" item — meaning it's application-dependent. Verify your factory shock droop travel before installation. If the shocks are near full droop already, order 67-3809 alongside this kit to prevent shock over-extension.

Why can't I stack blocks to get more height?
Block stacking creates a multi-piece stack that can shift, separate, or migrate under load — an unsafe condition that can result in sudden suspension geometry change under braking or cornering. Stacking may also be illegal in some states under motor vehicle safety standards. ReadyLIFT explicitly designs this kit to eliminate the need for stacking — a purpose-built single block at the correct height is the safe and legal solution.

Does this fit my Trail Boss or AT4?
The Trail Boss and AT4 models have different factory rear suspension configurations. Text (469) 407-7538 with your exact trim, model year, and drivetrain and we'll confirm compatibility before you order.

The Obsidian Take

The 66-3002 is the standard 1500-series rear block upgrade across nearly three decades of GM half-ton trucks — from the 1999 GMT800 through the current T1 generation. The net lift math tells the story clearly: 1999–2006 2WD owners get the full 2.25 inches; 2007–2024 owners swap out the factory 1.25" block and net 1.0 inch of additional rear lift. Both outcomes are valid depending on what you're building — the 1.0-inch net gain is the ideal complement to a 2-inch front leveling kit on a 2007+ truck.

The cast iron and anti-rotation ears are the product. Every competitor that makes this kit cheaper is cutting corners on one of those two elements. Cast iron at this weight carries factory-equivalent load capacity without the deformation risk of extruded aluminum. Anti-rotation ears prevent the pinion angle shifts and driveline vibration that a block without ears can produce over time under load cycling. ReadyLIFT built the ears in because that's how the factory block was built.

The two spring type checks on 2019–2024 trucks are the critical pre-order steps. The mono-leaf spring U-bolt identification takes 30 seconds. The composite overload spring check takes slightly longer — look at the spring pack. If you're uncertain about either, text (469) 407-7538 before ordering. The shock droop check is the third pre-order step that prevents a callback — verify travel, and order 67-3809 if needed before installation day.

This SKU is for: 1999–2024 Chevy Silverado and GMC Sierra 1500 6-lug owners (2WD and 4WD on 2007–2024 trucks, 2WD only on 1999–2006) who want to restore towing rake, pair a rear block with an existing leveling kit, or achieve a leveled lifted stance — running traditional steel leaf springs (square U-bolts) without composite overload springs, Trail Boss, or AT4 configurations.

This SKU is NOT for: 8-lug Silverado/Sierra 2500HD or 3500HD owners, mono-leaf composite spring 1500 trucks (round U-bolts), GM 1500 trucks with composite overload springs, Trail Boss or AT4 owners without prior confirmation, anyone planning to stack this block with the factory block, or anyone who hasn't verified shock droop travel before installation.

SAE J2492 Warning
⚠ WARNING: By installing this product, you acknowledge that the suspension of this vehicle has been modified. As a result, this vehicle may handle differently than factory-equipped vehicles. As with any vehicle, extreme care must be used to prevent loss of control or rollover during sharp turns or abrupt maneuvers. Always wear seat belts, and drive safely, recognizing that reduced speeds and specialized driving techniques may be required. Failure to drive this vehicle safely may result in serious injury or death. Do not drive this vehicle unless you are familiar with its unique handling characteristics and are confident of your ability to maintain control under all driving conditions.

Manufacturer Data Disclaimer
Product specifications, fitment data, and feature details are sourced from ReadyLIFT manufacturer documentation and verified third-party technical references current at the time of publication. ReadyLIFT reserves the right to modify product specifications without notice. Confirm 6-lug configuration, spring type (traditional steel leaf — not composite mono-leaf or composite overload), Trail Boss/AT4 status, and shock droop travel before ordering. OFAS is not responsible for incompatibility resulting from mono-leaf spring applications, composite overload spring applications, 8-lug HD truck misidentification, factory block stacking, or shock over-extension.

Prop 65 Warning
⚠ WARNING: This product can expose you to chemicals including lead and lead compounds, which are known to the State of California to cause cancer and birth defects or other reproductive harm. For more information, go to www.p65warnings.ca.gov.

Non-Returnable Notice
This item is non-returnable once installed. Verify 6-lug configuration, spring type, Trail Boss/AT4 status, and shock droop travel before ordering. Questions before ordering? Text (469) 407-7538.