What are Grease Zerks and Where to Find Them

Christian Spaccarotella
6 Minutes

Grease is an essential part in preventative maintenance, but it also plays a major role in the heavy duty vehicle industry. Most mechanical parts require grease, and wherever grease is needed, grease zerk fittings will be found. Zerks are the pieces needed to grease a heavy duty vehicle. There are many methods to greasing such as manual lubrication using a grease gun or manual pump, an automatic pump, or oil bath lubrication. The one that is most common and most accessible is manual lubrication with a grease gun. Of all the parts that branch across multiple systems like suspension and brakes, grease zerks are the most influential piece, yet the easiest to overlook.

What is a grease zerk?

A grease zerk is a relatively simple design. At its core, it's a fitting designed to keep grease within the mechanism. It pairs with a specialty tool, like a


grease gun, allowing grease to be injected into the mechanism at manufacturer’s specifications. Essentially, it allows you to put grease in a specific location instead of all over.

The basic design of the grease zerk is a nipple with a metal ball placed at the end of a spring. When pressure from the grease gun is applied to the fitting, the spring compresses removing the ball from the nipple opening and letting grease flow into the mechanism.

Where are grease zerks found?

To understand how to grease a zerk fitting, first you should know where they're located. The best way to find the zerks is to visually inspect the trailer. They are easily found on brake systems, but only drum brakes, not disc brakes. Breaking that down a little further, drum brakes have s-cams and slack adjusters that both need to be greased in order to complete the function of drum brakes. Disc brakes are operated by air, but are similar to your car brakes which have a rotor and caliper design-no grease is required for them to operate. According to FULLBAY who focuses on heavy duty equipment, these are the main places grease zerk fittings are found:

  • wheel ends
  • Hinge or pivot joints (hoods, covers, 5th wheel mounts)
  • 5th wheel plate and lock
  • Steering linkages
  • Drivelines
  • Clutch linkages
  • Pedals and levers

Zerks are found in all the major systems of heavy duty equipment, and they ensure that they stay functioning properly. Without greasing them regularly, pieces will wear down causing issues, causing brake failures and other systems failures that can lead to accidents like rollovers.

The Fifth Wheel

Since LGT is a trucking company, we should mention one of the most important places to grease on a semi truck. The fifth wheel despite its name is not actually a wheel, but rather a wear plate that connects your tractor to your trailer. It is the essential piece to hauling semi trucks, so in other words, you want this piece to function properly.

There is no right or wrong way to grease the fifth wheel. A grease gun could be used to apply the grease in a certain pattern. Some shops will use their hands with gloves to spread the grease out as well. Truck stops offer grease packets that you can put on your fifth wheel that will pop when connecting to the trailer king pin.

What tools do I need?

Multiple types of areas calls for different types of grease guns and fittings. The two most common grease guns are manually powered and air powered. Manually powered grease guns are a lever that uses seals to pump grease through the grease zerk, aka hand pump. Air powered grease guns use an air cylinder in place of the hand pump in order to apply pressure to the grease pump through the zerk.

Lastly, there are several different types of grease gun fittings to fit special applications. The general grease zerk pushing the ball back into the zerk and then applies grease. The second common type of grease gun fitting is a needle fitting.


This type of grease gun fitting allows you to add grease directly past the ball in the zerk and is designed for hard to reach areas. The best example of when to use this is with cryogenic trailers. The driveline has small u-joints that will not allow a standard grease gun fitting to reach the grease zerk. The only alternative our team has seen is grinding down the normal grease gun fitting on each side to allow access to the grease zerk.

How to fill a Grease Gun

A quick tutorial on how to fill a grease gun might be in order, since we are talking about greasing zerk fittings. There a few different ways to refill a grease gun. The first is the suction loading method. Where you partially submerge the open end of the gun into an open container of grease. Although it might be the most accessible to do on your own, it is not recommended due to the risk of contamination from the lid being open.

The preferred method for filling a grease gun is with a bulk fill manual lever pump.

This video will explain these processes in more detail.

Safety Tips for Lubricating

Lastly, some quick tips for when you finally need to grease your truck and trailer. Machinery Lubrication has a few helpful tips for maintaining your grease guns and fittings:

  • Use a clean cloth or rag to wipe the fitting before using it to clear any debris. Also use the grease gun caps to keep contamination out.
  • Make sure to inspect the grease fitting beforehand to know if any replacements are needed.
  • Conspicuously mark the grease fitting with the type of grease being used. Avoid changes where possible.
  • Learn proper grease gun operation and know the delivery volume per shot. Have grease guns calibrated occasionally to insure proper volume delivery.
  • Some grease guns develop pressure up to 15,000 psi. Exercise caution to avoid over packing and/or seal damage.
  • Keep guns clean, avoiding laying them on dirty surfaces. Repack on a clean bench using a gun loader fitting.
  • Keep grease guns covered when not in use.
  • Exercise caution to ensure safety. Make changes such as piping out fitting to avoid danger.
  • When repacking grease guns from a pressure line, wipe down the fitting and the pressure line to prevent contamination. When repacking with tubes, move to an environmentally controlled area, such as a control room, to replace the tube.

Properly greasing and maintaining your grease zerks is an invaluable practice in preventative maintenance. Their role of lubricating and ensuring things run smoothly is one of the most important aspects of vehicle maintenance, and learning what they do, where they are located, and how to lubricate them will set you on the right track.

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