expl0rer

Since there are so many threads about the liftgate and actuator, I thought I'd start a new one since I took the actuator apart to see what might be wrong with it and add some pics of the actuator guts.
In my case, the symptom started in the summer. The liftgate would not lock one evening (when I was replacing an airspring, but that's probably unrelated). The liftgate would move up and down with all buttons (located on driver door, fob and liftgate) and open with the handle on the liftgate as well. I let the liftgate simmer for a while and went at it again later in the evening. To my pleasant surprise, it was working just fine with the fob. I also tried the other buttons for good measure. All seemed to be back to normal. I did realize later that the second time I used the second fob. It seemed like whatever was causing this issue was somehow fixed by the second fob and the system was reset. I am just guessing here, no hard evidence to corroborate.

I don't recall exactly what type of sounds the motors were doing when this first happened. Yes, motors. There are two. More on that later.

Tools/supplies:
needle nose pliers with long nose (to comfortably hold the spring)
needle nose pliers with short nose to separate lower and upper assembly of actuator (optional and only recommended if you are sure the problem is in the lower part, which is not really easily serviceable)
screwdriver to push/pull hook of the actuator from unlocked to locked position
grease to apply on all gear wheels (plastic and metal), plastic contact points between shafts and housing (recommended). I was tempted to use chain grease for bikes, as it adheres to the surface and does not splatter all over immediately when rotational forces are in play.

There are lots of sources which describe or show how to remove the inside panels of the liftgate to gain access to the actuator for removal. I started with partial removal to expose the actuator and the bottom half to expose the manual release cable. I eventually removed all panels (top, side and bottom) as I had some plastic rivets on the liftgate and wasn't going to risk damaging them while contorting my arms, wrists and fingers in inconceivable ways and directions in feeble attempts to remove them. It made reconnecting the actuator and testing on the liftgate much easier and quicker as well.

Note some documentation I saw referred to the part which I called "horseshoe" or "hook" as "locking eye".

So a couple of days ago I used the liftgate to load some stuff and when I came home, I opened it to unload. The troubles started when I closed it with the liftgate button. I always use that button to close it. The liftgate would go down, but when it was time to lock, the motor would make three loud noises as if it was grinding. Usually the motors only make a solo sound. This was the first time I could hear the motors running and stopping three times. The latch would just not engage against the locking eye. When I opened the gate, it would make one sound, also similar grinding sound and move up to its usual position. I felt adventurous and decided to have a closer look at the guts of the actuator. I also found a video which explained some common problems with the actuator and how to fix them.


I actuator is two parts. The bottom part houses the hook which wraps around the locking eye. The top part is encased in plastic and houses gears. springs and two electric motors. I removed the lid by cutting the tops of the plastic rivets. Those are melted in place and easy to work with. I did not remove the rivets completely, as I was going to use their bottom part for screws to secure the lid back in place. To do that, I recommend drilling holes first and use small screws. There is little pressure on the lid, it holds in place the shafts of the plastic gears so no need to overdo it here with big screws. Hand tighten and don't overtighten. The lid's rivets are not designed to take much pressure.



You don't have to separate the bottom part from the top part. So don't open the "fingers" (arrows) or you will have to deal with aligning gears with your fingers to mate the two again. That was a pain in the !@#. If you have good dexterity, it may not be as annoying to you as it was to me. If actuator parts could fly, I would have been hit by all of them.

Now to the fun part. After cutting the top of the plastic rivets with a sharp blade, the lid came up very easily with minor prying. I was afraid that I would see (if I were lucky) or hear (if I were unlucky) parts springing in all directions as I removed the lid carefully. To my pleasant surprise, I experienced neither. Everything looked to be intact and in place.



Notice the two electric motors. one is vertical (you can see the metal gear on the shaft), the other is on the opposite side horizontal.

Not knowing what the problem might be, I started disassembling, removing the metal bracket. To remove the gear bracket, you have to
a. close/lock the actuator (by hand, just push the black hook with a screwdriver till it locks. If it does not, hold it with your left thumb in place. This will allow you to perform b.)
b. rotate the gear which makes contact with the vertical motor. Rotate it left/clockwise at least 75% of travel, the more the better. This will move the metal bracket out and away from another gear wheel which immediately to its right and closer to you. you now need to rotate this gear clockwise (or alternatively rotate the big gear to the right of the bracket counter clockwise) and hold it. You can now release the hook with your left thumb. It will stay in place as long as you are holding the gear to the right of the metal bracket. (Confused yet? It becomes second nature once you've done it a few times like I did, by then my fingers were all greasy and everything was super slippery. Several blessings were heard during this part).
c. you may lift the metal bracket out.

Everything comes out easily, so take your time and be patient, like most things Mercedes. I mean the "take your time and be patient" part, not the "comes out easily" part.

You may now release the gears you were holding by hand. If your actuator was locked on its own, it will remain locked until you release it using the long wire. Otherwise, it will spring back. To make it lock so you don't have to hold it (should be working like this anyway), refer to the video. The guy in it was very thorough, I thought.



Now you can remove the funky gear which was connected to the metal bracket. There is a spring which applies tension to this gear, you have to manipulate it (needle nose pliers are handy) by lifting and pulling the end of the spring away from the gear to release its tension. Then just lift the gear off the shaft. I did not see said spring in the videos I looked at. I might have just missed it, but I thought it would be wise to add a bit about it here.

There is a gear wheel between the funky gear and the big gear wheel to the right. Its shaft is actually held in place by the metal bracket I removed first. It is important to align it during reassembly. The part is visible in the video so I did not take pics of it. It's tall and has a smaller gear on top, larger on the bottom. All one mold of plastic. I removed that as well to check the hole where it would sit on the bottom. Luckily it was intact. I only had side to side movement, which is what you want (as per the video).

Since the actuator was not locking, I rotated the smaller gear wheel (see video) clockwise until I heard a click. I had to apply quite a bit of rotational force to get it to click. There is no chance I could do it with all gears and parts assembled in place. I tried that. I attribute having to do this part to me separating the bottom and top of the actuator. If I had not done that, I may not have needed to rotate that gear wheel for the lock. When I disassembled the bottom from the top, I head clicks, so some sort of spring action occurred, but I cannot be sure what exactly.





Arrows point to the "fingers" keeping the top and bottom parts together. Pliable with needle nose pliers, there is little space to use regular pliers with more leverage, but that wasn't necessary. Don't overextend them, just enough to clear the plastic housing.



There seem to be sensors (see arrows pointing to them) on the bottom of the assembly housing the electric motors which I think determine the position of the mechanicals living in the bottom part of the actuator and perhaps feed information to the motors to engage when necessary. They looked clean and I did not touch them at the time, but I did clean them later with dabs of contact cleaner and only focused on the surface of the sensors. The sensors are wrapped in clear epoxy of some type, the visible components are not exposed.




This is the lid of the motor assembly. In my case the lid had lots of displaced lubricant which I reused to lube the gears, shafts and holes, then got half of it on my fingers as I was fiddling with the gears several times. Leave the lubrication for the very end, unlike me. Use a little more than a little less. Don't use lots more.

While you have the actuator in front of you, look at the pins where the harness connects to the motor assembly for corrosion. I thought I could see some discoloration so I took some sand paper and carefully sanded all pins using the space between the two rows, both along and across each row of pins.

Reassembly time. Everything goes back together in reverse order. At this point my fingers were oily and everything was much less cooperative. More blessings were expressed several times. Even the dog left the room in contempt. I tested the lock/unlock before attaching the cap of the motor assembly, and after. I noticed that the hook was not moving as freely as it was without the motor assembly attached. I took it to the car to test the motors with battery power, unlike the test in the video. I did not remove the motors from the housing. The liftgate moved all the way down and locked, but did not retract fully. There was some play. Originally the locking eye, around which the actuator wraps its hook, was set to rearmost position (towards the rear of the car) minus 2-3 millimeters. I adjusted the eye on the chassis to inward most position (towards the front of the car). Tested again. Same outcome. The actuator did not want to fully disengage when the liftgate was opened with the handle on the liftgate. I could hear the motor working and the liftgate was trying to open (hydraulics in action) but it wasn't going far, it was only partially unlocking. I had to manually release the actuator using the handle on the inside of the liftgate.

I took the actuator off again and disassembled it. Upon close examination, I noticed that the funky gear which contacts the vertical motor did not make great contact with the motor's gear wheel. There is play on that funky gear and if I pushed it ever so slightly in the motor's direction, the gears were mating just fine. I did not think the teeth of the plastic funky gear were worn out, but I could be wrong. I can't be sure if the mating of the gears changes for the better with the lid on and all shafts aligned properly.

Here is where I cleaned the sensors, thinking that they were not feeding the correct data to the motors. More regreasing and reassembly followed, and back to the car for more testing. The locking eye was set to inward most position (towards the front of the car). This time the liftgate locked fine and left no play. Opening the liftgate, I ran into the same problem as earlier. The actuator did not release the eye fully. I opened the liftgate manually, then I changed the position to outward most position (towards the rear of the car). Closing was fine, no gap again. Opening liftgate - same problem. So now I can close the liftgate, but to open it, I have to climb in the trunk and use the manual release.

I suspect the left motor positioned vertically is not mating with the gear wheel. I believe that is the second part of the sequence to disengage the lock. From what I could tell, the upright motor starts the engagement sequence and the horizontal motor finishes it to lock the actuator. When the actuator is locked, the sequence is in reverse. So the locking works fine now, but the unlock is only working half way using the button on the liftgate. There is play in the liftgate when I try to unlock/open it, but the actuator does not fully release the locking eye. Next is to play with the locking eye's position to see if that might make a difference. Seems like the alignment between the eye and actuator might have to be spot on, based on some of the threads I had read through.

I ordered a new actuator before I got into the old one, so that will go on the car unless I figure a way to get the unlock to work via buttons.

Somewhat important to note is if you are doing the same thing as me, over a couple of days, disconnect the battery. Mine drained in approximately 36 hours. I had the car's four doors locked, but it was not armed as the actuator was not installed and the liftgate could be freely lifted/shut by hand. All interior lights were turned off.

The End. For now.

expl0rer

Update: I played with the locking eye adjustment today. MB was thoughtful enough to include notches on the eye base (both sides) to facilitate the adjustment. Nice touch. (no picture to show that, but easily visible on the base of the locking eye)

I tried 4-5 different placements of the locking eye, most of which did not result in any improvement. One got me close enough. I could close the liftgate (via the liftgate button) and open it via the handle. This particular time the liftgate opened, it seems like something tripped the lock gear in the motor assembly and I could not lock the liftgate any longer manually or via the button. So I took off the actuator again and opened the motor assembly. Sure enough, the gear wheel which locks the hook in the bottom assembly had been "rolled back". I set it again (turn clockwise till you hear a click) and decided to investigate the motors. Took both off (pull straight UP! especially the upright one. The horizontal one can be pried up with a short screwdriver). I tested the motors with 1.5V and 3V DC current, The horizontal one was not budging, but the vertical one happily spun up. Shafts were spinning freely on both motors. I also checked the continuity between the harness connector and the pins feeding power to the motors, as well as current from the harness connector to the motors when connected. Continuity was fine for both the horizontal and vertical motors, but only the vertical one responded to current.

As it stands now, the horizontal motor is caput! I am not sure I can source one (yet) and I might not try that immediately, but it would be nice to have a backup working actuator on hand if the new one which I haven't received yet decided to go caput as well. Next will be to take the motor apart and see if I can fix that. But that will be for another day.

Horizontal motor, sitting up above its bed after being pried up.


This is where it lives. The two pins sticking up plug into the motor and feed current to it.



Markings on the bottom part of the motor.



Edit: Apparently the motors are available for purchase. I ordered both from China for $35 CAD shipped, delivery sometime in the next century or two.

expl0rer

Today I got into the horizontal motor. It's rather easy. Pry open two tabs on each short side of the metal housing to release the white plastic cap. You can see them in the pics, sort of. The cap slides off. The copper coils, magnets and shaft remain anchored in the metal housing, which is good. In my case, I had a small copper tab and a copper ring/washer fall out as I pulled the plastic cap and metal housing apart. The washer had some solder on it, It seems like it should have been anchored with the solder, but had managed to break off. I close look at the shaft made it obvious where the copper tab came from. It is supposed to be attached to the bottom of the coils. You can see two more copper tabs like it in place in the pics below. It quickly became obvious that it would not just go back in place without taking the motor apart even more and some creative engineering/soldering. I didn't have the stamina to do all of that, especially since I have parts on the way. So I reassembled and plugged the actuator back in the liftgate to be able to least have the car locked until parts arrive. Once I have the motors in hand, I'll see if I can have a closer look at the sequence in which they are actuated when the liftgate opens and closes. The actuator definitely needs both to function, I'm curious to see if they are running simultaneously, in sequence, or a combination of.

The plastic cap, copper ring and broken tab. The cap had accumulated quite a bit of dirt inside. I used some contact cleaner to make it half presentable for the pictures.



The shaft with the other tabs in place, and the blank/black space where the broken tab should be. The copper ring slides over the shaft and should be next to the copper coils.

expl0rer

I haven't forgotten about this thread. Posting an update for those interested. I received the "spare motors" a while back and need to find a little time to swap them, then mount the "refurbished" actuator in the liftgate to test. Hopefully soon.

expl0rer

Finally had a little bit of time to get the horizontal motor replaced in the OE actuator and mount it in the liftgate to test. Plus the weather was gorgeous and made outside work pleasant. I did not have to disassemble any gears to replace the horizontal motor. When I tested the actuator, it worked like it should. The loftgate was smooth opening and closing. I did not bother replacing the vertical motor, as it was working fine when I tested it and replacing it also required disassembling some gears.

I ordered both motors just in case and because it was a package, IIRC. See above for details on the two motors.

So for ~ $30 CAD, I was able to repair the OE actuator. The price includes both motors. If you're replacing/purchasing one only, it will be even cheaper.

I now have a spare actuator with OE gears. If the Chinese actuator fails, I will see how well the quality of the internals is.

eric_in_sd

Outstanding thread. Thanks for all the info.

expl0rer

Thanks! I'm usually into cutting repair costs, but not at the expense of safety. If I were to do it again, I'd order the motors only and deal with a nonfunctional liftgate for a month or so till I could get the actuator repaired.

Tsumi

Thanks, lots of good info here. This should apply to the ML and R class liftgates as well.