Quick answer
Yes, rear lift blocks are safe when they're used on the rear axle of a leaf-spring truck, at a sensible height, with new U-bolts torqued to spec. They're used in many factory-engineered lift kits. Never use blocks on a front steering axle.
How lift blocks work
On leaf-spring trucks, the axle is clamped to the leaf pack with U-bolts. A lift block is a solid spacer placed between the axle and the springs. Longer U-bolts clamp it all together, and the rear sits higher by the block's height.
Why people use them
- To match a front leveling kit or lift kit so the truck keeps some rake.
- As the rear half of many complete lift kits.
- To add a little rear height on a truck that tows or hauls.
Keeping blocks safe
- Stay moderate: 1 to 3 inch blocks are common. Very tall blocks increase leverage on the springs and make axle wrap more likely.
- Use new U-bolts: kits include longer U-bolts; never reuse stretched factory ones.
- Torque to spec and re-check after the first few hundred miles, when everything settles.
- Tapered blocks correct the pinion angle so the driveshaft doesn't vibrate.
- Check shocks and brake lines: taller blocks may need longer shocks and brake line slack.
What is axle wrap?
Under hard acceleration or heavy towing, the axle can twist the leaf springs into an S shape, causing a hop or shudder. Taller blocks add leverage, so wrap is more likely. Traction bars or add-a-leafs help on trucks that see heavy use.
When to skip blocks
For tall lifts or trucks that tow very heavy, many owners choose new lift springs or add-a-leafs instead of tall blocks. For load support, helper springs are the better tool.
Shop rear block kits from ReadyLift, Fabtech and Skyjacker, or see all suspension.
Frequently asked questions
Do lift blocks affect towing?
They don't change your tow rating, but they raise hitch height. You may need a ball mount with more drop to keep the trailer level.
Do I need an alignment after installing rear blocks?
Rear blocks don't usually change front alignment, but if you're also leveling or lifting the front, get an alignment.
Aluminum or steel lift blocks?
Both are used in quality kits. Steel and cast iron blocks are very strong; aluminum blocks are lighter. Follow the kit maker's design.