How Many Pumps of Grease for Trailer Wheel Bearings? My Easy Explanation

When it comes to maintaining trailer wheel bearings, there’s often a debate about how much grease should be used. Some argue that over-greasing can lead to issues like elevated temperatures or the rollers sliding instead of rolling. On the other hand, some prioritize using grease as a protective barrier against dirt and water. So, the question arises: how many pumps of grease should be applied to trailer wheel bearings? 

The number of pumps of grease needed for trailer wheel bearings depends on the specific design and requirements of your trailer. While some people suggest packing the bearings full of grease, others advise using only a small amount. The key is to strike a balance between lubrication and avoiding over-greasing and basically, it ranges from 3 to 5 pumps on average.  It’s important to follow the manufacturer’s guidance and recommendations for your particular trailer and axle system.

Maintaining your trailer’s wheel bearings is crucial for smooth and safe operation. By understanding the appropriate amount of grease to use, you can ensure optimal performance and extend the lifespan of your trailer’s bearings. So, whether you’re a trailer owner or simply curious about the best practices for this essential maintenance task, keep reading to discover the answer to the question of how many pumps of grease are needed for trailer wheel bearings.

How Many Pumps of Grease for Trailer Wheel Bearings

Determining Grease Amount for Wheel Bearings

The amount of grease needed depends primarily on whether the trailer hub uses a grease zerk fitting or if the bearings are hand-packed.

Determining Grease Amount for Wheel Bearings

For Bearings with a Grease Zerk Fitting

Most small utility trailer axles have a grease zerk fitting on the end of the spindle. This allows new grease to be pumped directly into the cavity between the inner and outer bearings.

When lubricating these types of bearings, the generally recommended approach is to pump grease slowly while rotating the wheel until you see grease just start to seep out from the outer bearing seals. As grease reaches the outer races full of rollers and starts getting pushed out, that indicates adequate lubrication between the bearings.

It’s best to start with slow, small pumps on the grease gun, just half pumps at first. Go up to full pumps as you get close to the point where you see grease seeping. I typically add grease in 3-5 pump increments, spinning the wheel and checking for leakage each time.

The total number of pumps needed depends on the size of the hub and how depleted the old grease was. But most small 4.80 x 12 utility trailer tires require between 3-15 full pumps of the grease gun to adequately fill and coat the bearings.

For Hand-Packed Bearings without Fittings

Many boat trailers, larger capacity trailers, and vintage campers require manually packing wheel bearings by hand since a zerk fitting is not present.

When packing bearings by hand, the goal is to fill the cavities between the individual roller bearings within the inner and outer bearing sets. Work the grease thoroughly between each roller to displace any old contaminated grease.

Once the bearing sets are packed full, coat the inner races in the hub as well as the spindle surfaces with fresh grease before carefully installing the bearings. You can also put a very light coat of grease in the hub, between where the inner and outer bearings sit.

Why You Need to Grease Your Wheel Bearings?

There are two primary reasons why routine lubrication of trailer wheel bearings is so critical –

1. Lubricating and Protecting Bearings

The main purpose of adding fresh grease is to keep the inner and outer bearings properly coated. The lubrication reduces friction as they rotate at highway speeds, extending their service life. It forms a protective membrane to inhibit moisture and contaminants.

Without adequate lubricant thickness and coating, metal-on-metal contact occurs within the bearings as they roll. This greatly accelerates wear, tear, pitting, and eventual failure.

2. Contaminant Barrier

The other key job of the grease is to act as a barrier within the hub, keeping external contaminants like water, dirt, and road grime from ingress.

As you drive and create heat buildup in the hub, condensation forms which can carry contaminants deeper into the bearings if inadequately lubricated. The grease membrane blocks this deteriorating effect.

Reasons You Shouldn’t Over Grease

While complete lubrication is critical, adding too much grease can cause major problems including –

Overheating and Seal Failure

Excess grease has nowhere to expand as the bearings heat up at speed on the highway. The increased pressure can push out grease seals and lead to overheating. It may try to escape through the tiny seals, taking contaminants along with it back into the hub.

Indications of Too Much Grease

a) Fresh grease leaking out around the seals, usually slung along the brake assembly from wheel rotation

b) The hub feels abnormally hot after driving as grease cannot ventilate properly

c) A minor wheel end shimmy or vibration develops from grease imbalance

The key is using just enough new grease to coat components without overfilling the crowded hub.

How to Pump Grease into Trailer Wheel Bearings?

If your trailer axle uses grease zerks, here are the proper steps for refreshing the lubricant –

Step 1. Prepare Properly

Start by leveling the trailer, chocking wheels for safety, and verifying the parking brake is set. Then jack up the end needing maintenance and secure on adequate jack stands.

Step 2. Access Wheel End Components

Remove the plastic hub cap, cotter pin, and dust cap from the spindle end, and the spindle nut and flat washer. Pull the hub to expose the inner bearing and seal.

Step 3. Pump New Grease

Identify the grease zerk fitting on the end of the spindle. Wipe any grime off the tip so your grease gun nozzle can sit tightly. Firmly press the grease gun head to the zerk.

Slowly pump fresh grease while rotating the wheel periodically. Go in small increments, checking for leakage after each few pumps up to the recommended volume.

Step 4. Reassemble Properly

Once adequately lubricated, carefully repack the bearings and components in reverse order. Spin the wheel to check for smooth rotation without friction or noise before torquing the spindle nut.

Step 5. Final Steps

Install a new cotter pin through the spindle nut and bend the legs to secure. Reattach the dust cap and hub cap last after lowering the jack. Finally, torque wheel lugs to specification.


Bearing wear is unavoidably accelerated every mile a trailer rolls down the road. But proper regreasing techniques help reduce deterioration substantially between tear-downs. Using the manufacturer-recommended grease amount keeps components fully lubricated without the risks of overfilling. Checking hub heat and leakage signs allows for adjusting the volume as needed. Proactively maintaining wheel ends prevents costly roadside repairs down the road.

Frequently Asked Questions and Answers

How often should I grease my trailer wheel bearings?

A: Most manufacturers suggest fully regreasing every 12 months or 12,000 miles. Increase frequency for heavy-use trailers or commercial applications.

What type of grease should I use?

A: Always use a high-quality NLGI #2 lithium complex, multi-use grease rated for high-temperature wheel bearing applications.

What is the best way to check if trailer wheel bearings need to be repacked?

A: Jack up the trailer grab the tire at the top/bottom and shake aggressively. If you feel any discernible play or clunking, the bearings likely need to be fully cleaned and repacked.

Similar Posts

Leave a Reply

Your email address will not be published. Required fields are marked *