If you've ever spent an afternoon bolting a new rack to the floor, you already know that automotive lift shims are the unsung heroes of a functional garage. You can buy the most expensive, top-of-the-line two-post lift on the market, but if your concrete floor has even a slight pitch—which almost all of them do for drainage—that lift isn't going to sit straight. That's where shims come in to save your sanity and, more importantly, your equipment.
It's easy to look at a small piece of slotted steel and think it's just a scrap of metal, but in the world of heavy lifting, it's a precision tool. Most people don't realize how much a quarter-inch slope over five feet can affect the geometry of a car lift. When you're suspending several thousand pounds of steel over your head, "close enough" isn't really a phrase you want to use.
The Reality of Uneven Garage Floors
Let's be honest: perfect concrete doesn't really exist. Even if the slab was poured by a pro, most shop floors are designed with a subtle slope so that water and melted snow run toward the door or a drain. While that's great for keeping your feet dry, it's a nightmare for installing a lift. If you bolt the base plate of a lift post directly onto a sloped floor, the top of that post is going to be leaning.
When one post leans away from the other, you're putting massive stress on the synchronization cables, the pulleys, and the carriage bearings. You might notice the lift "chattering" as it goes up, or maybe one side locks into the safety teeth before the other. Most of the time, this isn't a mechanical failure of the lift itself; it's just a leveling issue. Using automotive lift shims allows you to square everything up so the lift operates exactly how the engineers intended.
Why Your Lift Needs to Be Perfectly Level
It isn't just about making things look straight. When a lift is out of plumb, the center of gravity shifts. Think about a two-post lift. If the posts are leaning even slightly outward, the weight of the vehicle is pulling on the anchor bolts at an angle they weren't designed to handle. Instead of a straight vertical pull, you're introducing leverage that wants to pry the bolts out of the concrete.
Safety locks are another big factor. These locks are mechanical catches that click into place as the lift rises. If the lift is crooked, the carriages might not hit those locks at the same time. You'll hear a click-click instead of a solid clack. If you're working under a car and one side is sitting on a lock while the other is still hanging by the cable, you've got a recipe for a very bad day. Automotive lift shims ensure that those safety mechanisms stay synchronized.
Picking the Right Materials for the Job
You'll see a few different types of shims out there, but for automotive work, steel is king. You might find some plastic versions used in lighter construction or window installs, but you don't want those anywhere near a vehicle lift. Under the pressure of a four-ton truck, plastic shims can compress or even shatter over time.
Most automotive lift shims are made from plated steel to prevent rust. They usually come in a "horseshoe" shape. This is a deliberate design choice, not just for looks. The slot in the middle allows you to slide the shim around the anchor bolt without having to completely remove the nut or lift the entire post off the ground. You just loosen the anchor slightly, pry the base plate up a hair with a crowbar, and slide the shim in.
They also come in different thicknesses—usually 1/16", 1/8", and 1/4". It's like playing a high-stakes version of Tetris. You'll likely need a variety pack because you never quite know how many you'll need until the level is sitting on top of the post.
How to Use Shims During Installation
The process is usually a bit of a back-and-forth dance. Once you've drilled your holes and set your anchors, you'll stand the posts up and tighten them down finger-tight. Then, you break out the long level or a plumb bob. You check the post from the front and from the side.
If you see a gap or the bubble on the level is off-center, it's time to start shimming. You'll slide the automotive lift shims under the low side of the base plate. The goal is to get the post perfectly vertical—or "plumb"—before you final-torque the anchor bolts.
One thing to keep in mind: don't just shim one corner. You want to support as much of the base plate as possible. If you only put a shim under one bolt hole, you're creating a pivot point that can cause the base plate to flex or the bolt to bend. It's better to use two or three shims spread out to create a solid, level foundation.
Signs Your Lift Might Be Out of Whack
Maybe you didn't install the lift yourself, or maybe it's been in the shop for five years. How do you know if you need to revisit your automotive lift shims? There are a few telltale signs.
First, listen to the sounds. A lift that is perfectly level usually sounds smooth. If you hear a rhythmic "thumping" or a grinding noise coming from the columns, the carriage might be rubbing against the internal tracks because the post is leaning.
Second, look at the wear patterns. If you see the grease on one side of the post is being wiped clean while the other side is untouched, something is crooked. Finally, check your locks. If one side clicks significantly later than the other, your leveling is likely off. Over time, concrete can settle or anchors can stretch slightly, so it's worth checking the level every year or so as part of your shop maintenance.
When Shimming Isn't Enough
While automotive lift shims are great for most situations, there is a limit to what they can do. If you find yourself stacking an inch of shims under one side of a post, you have a bigger problem. Most manufacturers have a limit on how high you can shim—usually around 1/2 inch.
If the floor is so slanted that you need a mountain of shims, the anchor bolts won't have enough thread engagement in the concrete. In those cases, you're looking at more serious fixes, like pouring a new reinforced concrete pad or using a non-shrink grout to create a level pedestal for the lift to sit on. Shims are for fine-tuning, not for rebuilding a foundation.
Don't Forget the Re-Torque
After you've spent the time getting everything perfectly level with your automotive lift shims, you're probably ready to start wrenching. But there's one last step people often skip: the follow-up.
New anchors and shims tend to "settle" after the lift has been used a few times. After you've cycled the lift with a vehicle on it ten or twenty times, go back and check the torque on those floor bolts. You might find that a shim has shifted slightly or the base plate has compressed down onto the shims. Tightening everything back up ensures that the level you worked so hard to achieve actually stays that way.
At the end of the day, using automotive lift shims is just about doing the job right. It's one of those small details that separates a professional setup from a DIY disaster. It takes a little extra time during the install, but it pays off every time you hit the "up" button and hear those safety locks clicking in perfect unison. Plus, it gives you that peace of mind when you're standing under a 6,000-pound diesel truck—and that's worth the price of a few pieces of steel.