RC Drivetrain Hack: How to Replace and Shim Bearings Properly

If you have upgraded your brushless motor, installed a high-discharge LiPo, and tuned your ESC to perfection, but your top speed is still lagging—you might be ignoring the most critical friction points on your vehicle.

Bearings are the tiny, hidden workhorses of your RC car. They support your wheel axles, differential outputs, and motor shafts, taking the brunt of every jump, power-slide, and crash. Over time, dirt penetrates the seals, the internal grease dries up, and the metal balls start to grind. A seized bearing doesn't just slow you down; it generates immense heat that will melt your plastic hub carriers and snap your driveshafts.

Whether you are trying to squeeze every ounce of speed out of a sprint car on the dirt oval or looking to bulletproof your 4WD basher, fresh bearings and proper shimming are non-negotiable. Here is how to swap and shim your bearings like a pro.

1. The Diagnosis: How to Tell if a Bearing is Blown

You shouldn't wait for a wheel to lock up before checking your bearings. Make it a habit to perform the "Spin Test" during your regular maintenance teardowns.

• The Spin Test: Take the wheel off. Remove the hex hub and the axle pin. Spin the bare axle with your fingers. It should rotate silently and infinitely smooth.

• The "Gritty" Feel: If you feel a crunching, sandy resistance, the internal balls are damaged or heavily contaminated. It’s time for a replacement.

• The "Wiggle" Test: Grab the axle and wiggle it up, down, left, and right inside the hub. If there is massive slop (movement), the bearing has collapsed internally or worn down.

2. Steel vs. Ceramic Bearings: Which Do You Need?

When it’s time to replace, you have two main choices. Matching the bearing to your driving style is key.

• Rubber-Sealed Steel Bearings: The industry standard for heavy-duty off-road bashing. The thick rubber seals create a physical barrier against mud, water, and fine dust. They have slightly more friction but offer maximum durability in terrible conditions.

• Ceramic Bearings: The ultimate secret weapon for dirt track racing. Ceramic balls are lighter, harder, and perfectly round compared to steel. They generate practically zero friction and run incredibly cool. If you are racing late models or IMCA modifieds where corner speed and rolling resistance matter, ceramic is the only way to go.

Check out Bermco RC Part's premium ceramic bearings here: 

3. Removing the Old Bearings

Getting a rusted or seized bearing out of a plastic hub can be frustrating. Never try to pry them out with a sharp flathead screwdriver, or you will gouge the plastic housing!

1. The Push Method: Take your 2.0mm hex driver and push through the back side of the hub, pressing evenly against the inner metal ring of the bearing to pop it out.

2. The Heat Trick: If a bearing is completely rusted and seized inside an aluminum hub carrier, do not force it. Take a heat gun or a hair dryer and heat the aluminum hub for 30 seconds. The aluminum will expand slightly faster than the steel bearing, allowing it to drop right out.

4. The Art of Shimming: Eliminating Slop

Dropping a fresh bearing into the hub is only half the job. Due to manufacturing tolerances, there is almost always a tiny gap between the wheel hex, the bearing, and the axle cross-pin. If your wheel can slide in and out along the axle, you have "slop." Slop destroys handling and causes the wheel to wobble at high speeds.

How to Shim an Axle:

1. You need an assortment of Axle Shims (ultra-thin metal washers, usually 0.1mm, 0.2mm, and 0.3mm thick) that perfectly match the diameter of your axle (e.g., 5mm or 8mm).

2. Install your fresh bearings into the hub, push the axle through, and insert the metal cross-pin.

3. Slide the axle back and forth. Take note of the gap between the cross-pin and the outer bearing.

4. Remove the pin and slide a thin shim onto the axle so it rests flat against the bearing.

5. Reinsert the pin and test again.

6. The Perfect Fit: Add or remove shims until there is zero back-and-forth play on the axle, but it still spins 100% freely. If the axle binds and becomes hard to turn, you have over-shimmed it! Remove a 0.1mm shim.

5. Installation and Lubrication

Before you press your fresh, perfectly shimmed bearings into place, remember these golden rules:

• Press Evenly: Always press a bearing in completely flat. If it goes in crooked, it will warp the metal casing and bind immediately.

• Oil New Bearings: Even brand-new bearings benefit from a single drop of premium, low-viscosity RC bearing oil. It displaces moisture and provides instant lubrication on the first run.

Roll Smooth, Drive Fast

A perfectly shimmed, fresh set of bearings transforms an RC vehicle. Your top speed will increase, your motor will run significantly cooler, and your cornering will feel locked-in and precise.

Upgrade Your Rolling Resistance! Stop letting blown, gritty bearings hold your chassis back. Whether you are looking for ultra-durable rubber-sealed kits for your backyard basher, or high-performance ceramic bearing sets to dominate the dirt oval, head over to the Naughty Boy RC online store. As your dedicated online warehouse, we stock the premium bearings, precision shims, and dedicated lubricants you need, shipped lightning-fast straight to your door.