2010 Mercedes-Benz ML550 Liftgate Support Strut Replacement Cost

A support strut is the long tube that causes the gentle hissing noise when the liftgate, hatch or hood is raised. Liftgate support struts are perhaps the most heavy duty of all of these due to the sheer weight of the liftgate which they must support. They are attached to the frame and liftgate, and when the liftgate is opened and closed, they extend and contract respectively. They hold the weight of the liftgate while opening and closing, and prevent the liftgate from falling in its raised position. These are very effective tool for ease of access to the liftgate assembly, as the assemblies tend to weigh well over 150 lbs.

Since the liftgate support strut is attached to the liftgate and the chassis of the vehicle, the support struts must be able to extend and retract without bending or breaking away from the mounts. Also, due to the weight of the liftgate, they must be able to hold weight, yet be balanced enough to allow the average person to pull the liftgate down. For these purposes. the part was designed as a very small shock absorber. Filled with inert gas or hydraulic fluid, this strut (or shock) is always attempting to extend itself. Internal pressures push two rods against each other, and one is mounted inside the other one. This causes the liftgate to be very easy to lift, as the support struts are doing most of the work. however, the liftgate struts cannot be too strong. They must only have enough force to push the liftgate open, with the addition of a few additional pounds amount of pushing force. This prevents the liftgate from falling when the wind blows, or if someone bumps it while it is open. When the liftgate is closed, one half of the strut will slide back into the other half, being forced by the user placing constant pressure on the liftgate until it is closed.

We have all noticed an old car with a stick holding up the hood or hatch. That is because the owner has not replaced the support strut for that component. Also, if you have ever tried opening a liftgate or hatch, and the support strut had failed, you would know immediately as the entire weight of the hatch would be resisting the lifting action. Also, the end of one of these liftgate support rods may be rattling around while driving, and opening the liftgate may show it is swinging freely, or falls off completely. When they separate from their mounting points, this is sure to happen.