Leaf Spring Sag and Replacement: Diagnosing Ride Height

Start with a walk-around before you ever put the truck on a lift. Uneven stance — one corner sitting lower than the others — is the most obvious tell. Stand back 15-20 feet and look at the truck square from the side and rear.

Other signs to check for:

• Visible gap or separation between leaves in the pack, especially near the center bolt
• Rust streaks or shiny wear marks where leaves are rubbing against each other abnormally
• A leaf sticking out past the edge of the pack — this usually means one has cracked
• Clunking or popping noises over bumps, which often means a broken leaf shifting
• Uneven or accelerated tire wear on one side, a downstream symptom of a sagged spring changing your alignment geometry
• Bottoming out on moderate bumps when loaded, when it never used to

If you find a fully broken leaf, don't drive it any further than you have to. A broken main leaf especially can lead to loss of axle control.

Eyeballing it gets you in the ballpark, but if you're diagnosing sag for a warranty claim or trying to decide if a spring needs replacing, you need real numbers.

• Park on a flat, level surface — this matters more than people think, even a slight grade throws off your reading
• Measure from a fixed reference point on the frame straight down to the center of the axle, or to the ground depending on OEM spec
• Take the measurement on both sides and compare side-to-side, not just against a spec sheet
• Check the load — measure empty and loaded if you can, since some sag only shows up under weight
• Compare your numbers against OEM spec for that make, model, and axle position — front and rear specs are different, and steer vs. drive axle specs are different too

Write down what you find. A half-inch difference side to side is worth investigating. An inch or more, and you're looking at a spring that's done its job and needs replacing.

Front leaf springs and rear leaf springs don't fail the same way or get replaced for the same reasons, so don't treat them identically.

Front springs carry steering geometry along with weight. Sag up front changes caster angle, which affects steering feel and tire wear fast. If you're seeing cupped or feathered tire wear along with a low front end, the spring is likely part of the problem — but remember, steering geometry work is safety-critical and any adjustment or diagnosis tied to steering angles should get signed off by a certified tech.

Rear springs typically deal with more raw load-carrying duty, especially on straight trucks and trailers. Sag here shows up more in ride height and axle wrap under acceleration/braking than in steering feel.

When you're replacing one side, seriously consider replacing the pack on the other side too, even if it's not showing the same wear. Springs age together under the same duty cycle, and mismatched stiffness side-to-side creates handling that's uneven under load or in a hard stop — again, tie this back to a qualified tech since it touches braking and handling behavior.

This is where a lot of guys get burned buying based on price or a rough cross-reference instead of the actual application.

• Match the capacity rating to your GAWR (gross axle weight rating), not just what fits physically — an undersized pack will sag again fast under real load
• Match leaf count and arch to OEM spec for your chassis; more leaves isn't automatically better if it changes your ride height or spring rate outside of what the axle and steering geometry were designed around
• Check taper leaf vs. multi-leaf design — taper leaf packs ride softer and lighter but aren't always rated for the same capacity as multi-leaf in heavy-haul use
• Verify eye-to-eye length and mounting style matches your hanger and shackle setup exactly — this isn't a spot to eyeball a close match
• Buy from a supplier who can confirm the pack against your VIN or axle tag spec, not just a generic size chart

When in doubt, pull the tag off your old spring or axle and match specs directly rather than going off memory or a rough visual comparison.

Swapping a leaf spring pack isn't just unbolt-and-bolt-back-on. Once new springs are in, ride height, axle alignment, and often wheel alignment need to be checked and corrected. New springs sit differently than worn ones, and that changes pinion angle, caster, and toe.

• Torque all U-bolts and hanger bolts to per OEM spec — under-torqued U-bolts are a common cause of leaf spring pack failure shortly after replacement
• Re-check ride height after installation and let the truck settle overnight before final measurements if possible
• Get a full alignment check afterward, especially on steer axles
• Inspect and replace worn bushings, shackles, and pins while you're in there — reusing worn hardware on a new spring pack is a false economy

Because this work directly affects wheel-end stability, steering control, and braking behavior under load, final installation and alignment should be signed off by a certified tech before the truck goes back in service.