Suspension Block and U-Bolt Kit

How lift blocks work

On a leaf-spring truck, the axle normally sits against the spring pack. A lift block is a spacer placed between the two, which raises the rear of the vehicle by the block height. Longer U-bolts hold the axle, block and spring together. Block kits are a simple, widely used way to level a truck that sits nose-low or to add rear lift to match a front lift.

Cast, fabricated, flat and tapered

• Cast iron blocks: OEM-style and common, often with an integrated pin and in some cases a bump stop.
• Fabricated steel blocks: made from steel plate and sometimes powder coated.
• Flat blocks: keep the axle angle as it is.
• Tapered blocks: angled so the axle pinion can be tilted back to reduce driveshaft angle.

Listed heights here run from 1 inch to 6.5 inches. Note that taller blocks increase leverage on the spring and axle, and tall blocks can cause axle wrap, so many people prefer new springs for larger lifts.

What to check

• Block height and taper angle.
• Spring width and U-bolt thread size and length: examples include 9/16 inch and 5/8 inch threads.
• Center pin style: single or double pin and size.
• Driveshaft type: some listings mention they are only for trucks with two-piece driveshafts, which may require a carrier bearing spacer.
• Air spring compatibility: some blocks do not suit factory or add-on air springs.

Installation and safety

Support the frame on jack stands and the axle on a separate jack. Replace the U-bolts with the longer ones provided, tighten them evenly in a crisscross sequence to specification, and recheck after driving. A lift changes driveline angles, brake line length and headlight aim, and may need shock extensions, so plan for those items and an alignment. A rear lift that is too large without the matching front lift can upset handling, and suspension modifications are safety related, so use a professional installer when in doubt. Check state regulations on vehicle height.

Consider how a lift affects the rest of the truck. Raising the rear without changing the front can create a rake, which alters headlight aim, steering feel and the way the truck handles under load. Many owners pair rear blocks with front leveling to keep the stance even. After installing blocks, check the driveshaft angles at the transfer case and axle, since a higher axle can cause vibration, and confirm brake lines and the parking brake cable are long enough for full droop.

Blocks also change how the axle responds to torque. Because the spring now sits farther below the axle, hard acceleration can cause axle wrap, where the housing twists and the spring becomes S-shaped. Traction bars or similar parts can help control this. Always use the supplied U-bolts and nuts and never reuse old ones, and recheck torque after the first few miles, because spring packs settle. Rust on the spring perch and the block seat should be cleaned off before installation so the surfaces sit flat.

Fitment

Match your exact year, make, model, cab and axle width to the product listing and manufacturer's specifications before choosing a product below.