Leaf Spring Axle Shim

The leaf spring axle shim or wedge is the part of your leaf-sprung vehicle that modifies the angle between the leaf spring itself and the spring perch on the axle. Getting shims is the preferable and affordable option to cutting the spring perches off and welding in new ones on a corrected angle, which takes a lot of work and requires a lot of careful measurement.

Dos

• Before buying your leaf spring axle shims, you need to first know what angle to make your shims in. You need to measure your driveline angle before and after suspension modification first. This will serve as your baseline measurements to restore your ride back to normal alignment after modifications.

• If you forgot to make measurements, then measure the height difference of the front-rear on the spring perch then get the perch's length. From those measurements, you can work out an angle. For instance, if your 6-inch perch has a 1.5-inch difference, then you need a 14-degree angle shim.

• Buy only the highest quality shims made of topnotch billet aluminum that's about aircraft grade in composition. After all, choosing a brittle cast alloy shim is like flirting with death. It can be a pain to have your rear axle shims break on the trail; however, it could be downright fatal to have your shims break on the front axle.

• To be more specific, get a nice solid billet aluminum shim blocks with built-in angles. This solid material ensures that your vehicle is held up even when faced with the heaviest of loads from the biggest and most rugged of vehicles.

• You can also purchase lift blocks as shim variants for trucks with a spring-over axle up front and a spring-under axle on the rear. They add drop to a spring-under axle and lift to the spring-over axle. For the sake of correcting the pinion angle, they might even have a bevel cut in the top.

• You can even ask for made-to-order shim customizations composed of mild steel if you feel that the available commercial shims are low-grade and have limited angles. Steel shims are more breakage-resistant and could ensure better fitment.There's the option to weld the steel shim to the spring perch to eliminate worries about shims falling, twisting, or breaking on the trail.

Don'ts

• DON'T buy the first shim set you seefor your leaf spring axle. To be more specific, you need an exact angled shim instead of just the default angle or two provided by shops both online and offline. Shims come in three, four, six, and eight degree angles.

• DON'T buy cheap cast alloy aluminum that easily breaks for your shimming needs. Instead, go look for a nice strong billet aluminum that's almost comparable to steel in strength but absolutely outdoes it in terms of corrosion. You don't want easy-to-dent and warp-prone shims that are as brittle as rusty iron in your car.

• DON'T stack up your shims or lift blocks. This will cause themto become more likely to collapse if your U-bolts are only even slightly loose. Speaking of which, your longer U-bolts have a tendency to stretch and loosen up, which necessitates the occasional re-torque for safety's sake.

This modification might be required for your ride when your pinion is out of alignment due to the angle where your longer spring shackles are bending. It's also useful in correcting steering geometry or shifting from a single-cardan to double-cardan driveshaft as well, among many other reasons.