Liftgate pump and motor assembly guide

PS, before reading, please read our Disclaimer at the bottom of this page 😊

What you'll discover in this article:

• What is a power unit?
• How do I find the correct parts for my power unit?
• Should I purchase a new power unit or rebuild mine?
  • Purchase new if your primary business needs to get back to work asap
  • Purchase new if many pieces of the power unit need to be replaced
  • Possibly attempt repair if…
  • Consider a repair when…
• Are there Universal Power Units?
• What are the basics of maintaining a power unit?
  • Ensure proper voltage
  • Confirm proper voltage and the ground
  • Change the fluid
• What’s next?

A power unit, also known as a pump and motor assembly, is the source of power for your liftgate’s overall operation. It converts the electric power into hydraulic pressure to operate your liftgate.

The liftgate power unit consists of a hydraulic pump, an electric motor, a reservoir, along with motor solenoid and control valves required for the pump to operate. When the motor is activated, it drives the pump, which pressurizes the hydraulic fluid. This pressurized fluid is then directed to the hydraulic cylinders, which extend and lift the liftgate.

Most single liftgate pump and motor assemblies come with a motor, motor solenoid, pump, valves mounted to the pump, and a reservoir.

Dual power units can be a bit more complex and may require other individual components. On dual units, there is commonly a primary power unit that will have a pump, motor, and reservoir; in this setup, the secondary power unit may only include a pump and motor. In that case, there may be an independent valve manifold with steel lines attaching to both primary and secondary units; the responsibility of this manifold is to help control the two power units. In a dual configuration a selector switch may be present to designate which pump is used, so that the power unit will operate one at a time.  

If you don’t have a detailed breakdown of your power unit to locate the parts needed, contact us today, we’re here to be your guide! Finding a detailed parts manual of the power unit to locate the individual components ensures the correct parts are provided.  

We’ll need a few key pieces of information from your liftgate to get started. Fill in the form below and we’ll be in touch shortly with next steps to fix your liftgate.

Like everything, it depends!

Purchase new if your primary business needs to get back to work asap

LiftGateMe is customer centric and always has our customer’s business in mind when offering advice. Saving money upfront is wonderful, but if an end user’s liftgate is vital for their main business to function, the time and effort to repair a power unit can quickly outweigh the cost and security found in purchasing a new unit.

Purchase new if many pieces of the power unit need to be replaced

Replacing the complete power unit is usually the most cost effective way to purchase the parts as they are cheaper together than individually. Doing so will save you time and frustration if you need to get back on the road asap and want to avoid troubleshooting the same issue twice.

Possibly attempt repair if…

If the reservoir is leaking, we can help! Most reservoirs are individually available, so replacing the entire unit can be avoided.

If a line or a fitting is leaking, those are commonly individually available. Contact us or consult your parts manual to locate the part number to order.

Consider a repair when…

If a seal fails, it may be more complicated. When this happens, the power unit may need a full disassembly and inspection to see how much damage was caused; during this process, an assessment of how much damage was caused to other parts of the system is needed as well. This is required because a damaged seal can send fluid right into the electric motor, causing it to short out or worse, catch fire if not taken care of properly! When fluid leaks out of a power unit, there is also a high probability that contamination will leak into it. This can cause many other failures; at this point, we often recommend replacing the complete power unit.

Whether you’re looking to replace the complete power unit or looking for an individual item, we’re here to help and relieve your stress. Fill in the form below and we’ll get you started now.

There are no “universal” power units for the liftgates.  

All liftgates have a specified pressure rating, function, and voltage. The pressure rating is calculated by a combination of four factors - the internal pump, the RPM of the motor, and the torque the motor outputs to the pump, and the amount of fluid it moves. The liftgate’s lifting capacity, speed, flow, and safety will change when any of these variables are altered which is why at LiftGateMe, we only sell OEM parts verified by the manufacturers.

Each power unit is so specific that several manufacturers, for many of their power units, do not offer individual components other than the motor, motor solenoid, or locking valve. They do this for your safety! If the wrong seals are used on a pump, it can cause bypass leaks which can lead to part failure and safety concerns. Improper seals can cause issues such as the liftgate jogging or jumping when in motion, the liftgate falling on its own, or, by causing leaks in other locations because the seals do not have the proper pressure to “lock” things in place. Purchasing the incorrect seals to save a few dollars can result in higher costs and, worst of all, cause safety issues.

Ensure proper voltage

Ensuring proper voltage is one of the largest factors in maintaining a power unit!  

Confirm proper voltage and the ground

Confirming the proper voltage and the ground, going to the unit, is one of the best methods to prevent a failure and is at the heart of the system.  

If your power and ground are insufficient, there will be a drastic difference in hydraulic output which can lead to breakdowns. For further help on power issues, we created a post, 6 step solution to ensure proper liftgate power, which can be found here to further assist.

Change the fluid

If there’s a leak or possible contamination, changing the fluid in your power unit is extremely important.  

Most power units have access to a drain plug on the bottom (just look underneath the power unit for this 😁); additionally, to access the drain plug, the pump housing commonly has an access hole.

Many power units have a decal noting how much and what kind of fluid to use. This information must be adhered to for your safety and the integrity of the gate. For more information on liftgate hydraulic fluid, check out this article - Liftgate Oil Guide.

If the whole system needs to be drained and refilled and you are unsure how to proceed, contacting the manufacturer may be the best way to get that information through their tech support teams.  

We recommend making sure you are fully aware of this process, before getting started, to ensure your safety and to prevent further damage to the liftgate systems.

When disassembling a motor from a pump, two main issues can occur. First, the end bearing for the motor drive may get stuck and seize inside the pump. Second, if the motor is pulled too far, the armature of the motor may fall out of the motor brush assembly. Be wary of both because cutting corners at this point can lead to larger issues.

Seized End Bearing inside a Pump

When removing a motor, you may find the end bearing is seized in the pump. At that point you know the motor needs to be replaced if its attaching parts are seized. If you decide to replace the motor and not the bearing/leave the original stuck in the pump and remove the new one from the new motor, there is a possibility that the bearing will fail. This can cause damage to other components. Our OEM motors come with new bearings preinstalled on all motors. So it’s best to do it all!

If the end bearing is lodged in the pump, there are only a few tedious methods to attempt to remove the end bearing without damaging the pump or pump shaft. One method is to weld a bolt to the bearing and try to pull it out and is commonly the most successful. Either way, our mechanics usually have their welders ready! Often this does not work since the end bearing is steel and seized to the aluminum pump through galvanic corrosion. At this point, we usually recommend replacing the pump.

Dislodged Armature

If the armature comes out of the motor’s end bell and brush assembly, a full inspection is needed to assess the condition of the armature and brushes for damage. In this case, the armature could be gauged or cut and the brushes can even be cracked and/or broken.

Reseating the brushes to put the armature back in place, requires a LOT of patience since this process is commonly done by a machine! Most people that have to reseat an armature on a sealed motor commonly bring it to an armature shop, which costs more money and more time.  

Our View

Trying to resolve either of the previously mentioned issues is most likely not worth the hassle nor potential damage so we often recommend replacing the motor and provide our customers the fastest way to get back to their business.  

The fact is that many of our customers need their liftgates working asap and need the reliability of a new motor so the cost of a mechanic’s sacrificed productivity and the business cost of an inoperable liftgate quickly outweighs the cost of a new motor.

One final word - even though many of our mechanics are more than capable of solving these hard problems, we will always have our customer’s needs at heart. Some of our customers can wait for a motor to be repaired because of limited (or even surplus) resources in which case we do our best to attempt the repair; however, a down liftgate for other customers may cost them thousands of dollars per hour and they look for the most efficient means possible to get their liftgates functioning. Listen to your customers and ask what’s important to them - that may help dictate the best solution.

Pump replacement
You may have luck disassembling the motor from the pump, and only the pump may be your problem, but most often, when a pump fails, the internal gears are what get destroyed.

When this happens, debris is frequently sent through the hydraulic components. This can cause a lot of damage to any part, if not handled correctly so it’s vital that all components are removed for inspection and cleaning.  

If metal debris makes it to a lock valve or spool valve, it can get into or through the small mesh filter on it, causing that part to fail as well. If the debris were to make it past that point, it could make it all the way to the cylinders, ruining the seals or shaft on them, causing further leaks or worse, cylinder “bleed down” (cylinder not staying in up or stored position/gate falling on its own) and this could wreak havoc on anyone's day!

Due to these reasons and more, we highly recommend replacing the whole power unit. This will help to ensure the least amount of down time and help reduce other potential part failure.

The power unit is one of the most important pieces of your liftgate and when it malfunctions, not only the liftgate, but your (or your customer’s) business may be unable to function; we know it’s not fun, but luckily, we’re here to guide you through the process of finding you the best solution that meets your needs.

We sell only 100% new OEM components and most single pump units come with all the parts you need to complete the job. We can also help you find the right parts for your dual assembly system as well!  

In any and all cases, we’re here for you! Just contact us with your gate ID tag info of the model and serial numbers, and we’ll help you along the way!

Whether you need a complete power unit or a piece of one, we have you covered. Fill in the information below to get started.

Disclaimer: The content of this article and website is available for informational and educational purposes only. It is not intended to be a substitute for the professional advice of a mechanic who has personally inspected your vehicle, liftgate, or any property, nor does it create a relationship of any kind between LiftGateMe and you. Every situation may be different, and LiftGateMe does not make any warranties, whether express or implied, as to the accuracy, fitness, or applicability of the information, liftgate, vehicle, parts or other property, portrayed in this article and website. LiftGateMe makes no guarantee of results or outcomes. LiftGateMe will not be liable for any damages related to personal injury, property damage or loss of any kind that may result from the use or reliance of our information and/or any automotive parts represented. You are using the information and automotive parts portrayed in this video solely at your own risk.