Hatch Door Actuator: Plastic Stuff, Warning don't do this!!, Easy to Change.. Thanks raybenz..
First of all thanks raybenz for your comments. It made me realize that the actuator was broken..
Warning..., Never open your hatch door at the same time you are unlocking the doors. After checking and testing the broken hatch lock actuator assembly, I found that if you try to open the hatch door at at the same time you are unlocking it, it makes the electro magnet mechanism pull very hard on a plastic locking mechanism rod piece, making it very prone to break. I am always racing my daughter unlocking the hatch door before she tries to open the hatch since she is always ahead of me. I think it was in one of these situations that the actuator broke. That is when she was pulling the lever and I was unlocking the hatch at the same time. The internal mechanisms stiffss itself in this situation and the elector magnet pulls too hard on a plastic piece that connects to the locking mechanism and sooner or later will break.
If it breaks then the door can unlock, since the electro magnet can push the locking rod, but it will not be able to open, since it cannot pull the rod since the locking rod is not attached to the electro magnet assembly anymore.
I found that the locking assembly is made in Germany, so in this case it may not be some of our cheap plastic American parts. I think there is a small design stress problem that happens in the odd situations when one is unlocking and opening the door at the same time. I was playing with the old assembly and could feel the increased pulling force needed to be done by the electro magnet to unlock in these odd situations, and unluckily the link between the electro magnet and the locking assembly is a piece of plastic.
Said that, the actuator assembly is about $70.00 at the dealer, and it is relatively easy to change. You need first to remove the lower plastic back from the hatch door. It is attached by plastic fasteners. You may want to get spare of these fasterners, because some of them may break. I broke one. There are two types of fasteners you may want to get.
The actuator assembly contains not only the electro magnet but the hidden outside black handle itself. That is, the internal black handle that you pull from outside to open the hatch door.
Once you remove the back plastic cover, you need to remove a couple screws and remove the outside decoration handle decoration, which is attached from inside by two screws. You need to remove the outside handle decoration because it hides two screws that hold the actuator assembly.
Once you remove all the screws and nuts holding the actuator, you need to remove the three electrical connectors, which is very tricky. I ended up breaking some of the plastic from the old connector assembly.
Puting back the internal handle ( the other handle that pops up from the inside once you remove the two supporting screws ) is a little bit tricky, too. The ML has to be locked in order to make it easier to put back all the moving pieces.
In all, it takes about 30-50 minutes at an easy pace. Once you know how to do it, I am sure it may be done a lot faster..
AC
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2005 ML 500
Black, 18" AMG Wheels, 285/60R18 Yokohama Geolander HTS + Bi-Xenons(+ Drew's e-code mod, though the reflectors rusted off and do not give out much light anymore), Yakima roof bars. Former vehicle 2001 ML 320 with 108K miles, when traded, and a large repair/defect history. After 3 years of owning my current 2005 ML 500, it has become another major unreliable vehicle with a very large/expensive repair/defect history..
Warning..., Never open your hatch door at the same time you are unlocking the doors. After checking and testing the broken hatch lock actuator assembly, I found that if you try to open the hatch door at at the same time you are unlocking it, it makes the electro magnet mechanism pull very hard on a plastic locking mechanism rod piece, making it very prone to break.
My unit has been apparently broken for years. I've just never noticed it before. The process is not too dificult - less than an hour if you don't have a clue about what you were doing (which was my case) and are being extra carefull not to break anything. Now that I know the process is quite simple. The hardest part is removing the inside plastic trim.
One slight errata in the above - it is if you are holding the handle and locking the door that breaks the part. Not unlocking. The whole of the locking mechanism is in the handle itself. There is a lever that flips to engage the handle. When it is unlocked and the handle is pulled the lever is blocked by a plastic extrusion and cannot rotate. At this point the actuator is pulling on the lever and the plastic connection breaks. Going the other way there is no tension on the lever and the actuator can still move with the handle pulled (though parts do spring out of connection. But excercising the handle once causes things to pop back into place).
Goofball German engineering again? Well, not really. Someone was still thinking here. There is a microswitch that tells when the handle is pulled and this will stop the system from locking. However the switch does not engage until the handle is at least 50% pulled and so as AC_ML mentions if someone is starting to pull the handle at the exact point that one is locking the door this part will break.
I was hoping that there would be a simple part that could be machined to be more robust. However the sealed solenoid and small size of the part makes a solution more of a pain then I want to deal with right now.
Since that plastic extrusion is causing the problem why have it there in the first place? It appears to only prevent you from manually locking the door with the handle pulled. Since the entire of the locking mechanism is in the handle assembly itself, that one locks the door with the handle pulled doesn't harm anything. If the door is locked with the hatch open you can still close it and it will latch. The lock has nothing to do with whether the latch itself is working or not. Perhaps it was left in some old engineering spec from decades ago and never removed?
Actually, I just thought of a semi-valid reason. That part prevents someone from drilling a hole in the plastic underneat the handle and pulling the open lever and opening the door with it locked. However if someone drilled a hole then could just as easily slide the lock mechanism over and so it really appears to be useless.
It appears that with a little patience one could grind that part down and solve the whole problem. I am going to attempt to repair the unit I have now with epoxy adhesive. If the fix does not last and I have to buy a new unit I will expoxy it again and test to see whether everything works fine with that extrusion missing. Or if someone has an old broken one they don't mind sending to me I'll test it on the spare.
Well, the epoxy did not bond to the plastic. The bottles were pretty old, though. I will try with a different/newer batch today. It appeared to work fine in testing out of the vehicle and when installed worked about 4 times. On the 5th exercise it pulled apart. I was able to peel the epoxy off with little effort.
There's a pic attached showing the solenoid removed with the broken part.
I considered running a small screw through the center of the part to help hold it to that plate but will wait to try the other epoxy.
Last edited by Gene Horr : 10-15-2008 at 09:18 AM.
I appreciate the tip on the Loctite product. If try 2 doesn't work I'll give it a go.
I tried a NAPA/VersaChem product called "Plastic Welding System". I also drilled out the white plunger part for a bolt and nut. See pictures attached. I drilled a hole using a 5/64" drill and tried a #2-56 x 1/2" bolt. The bolt threaded into the hole quite securly, which was good as the hole wound up being so close to the shaft that I could not get the nut on it. If you try this yourself you might want to angle the hole away from those side shafts on the plunger. There is enough play in all of the parts that the end piece can be slightly off and still work.
The product cures in 1 hour and I will try it then and post the results.
BTW - sorry for the poor quality of the photos. I no longer own any macro lenses nor extension tubes and have to shoot this from far away. And only having a single chip camera doesn't help.
It's been almost a week and at least 50 actuations. The repair is still holding so at this point I am reasonable confident that it will last.
The following is a step-by-step description of the removal process. I don't recall seeing this written before.
1) Obtain replacement "christmas tree" clips. At least 5 but better yet 10. Some will break when you remove them. I used some generic clips from NAPA. They worked but the OEM are much better.
2) Remove the center brakelight cover. You squeeze in on the top sides to pop it out. See picture.
3) Remove the inside door latch trim cover. The screw is obvious. See picture. After remove the one screw you may need to pry on the trim to pop it out.
4) Pull off the inside door cover. A trim tool prybar is helpful. Those clips hold on so well that many of them will break rather than pull loose. At the top of cover where it slopes up around the window frame there are two pins. You can try removing them first. I just popped the cover out of the bottom attachments then pulled the pins out. See picture of pins.
5) Remove the trim cover over the license plate that holds the license plate lights. There are two screws outside and then two nuts on the inside that hold it on. You'll probably need to pry the light plugs off with a flat head screwdriver. Those things were a pain to take off.
6) Inspect where the cover touches the door. In my case it had worn through the paint and there was a bit of surface rust. See picture.
7) Remove the inside latch handle. There is one screw holding it in place. You'll need to pull the latch out as if opening the door to reach the screw. The handle assembly has two clips that slide onto the door. This is also pretty tight and you may need to pry a little to get it off.
8) Remove the actuature assembly by unscrewing the two screws on the outside next to the handle. These screws were covered by the cover mentioned in #5.
9) Unplug the wires to the actuator. These things were also a pain to remove and you may need a third hand to hold things. Note which plug goes where and the orientation.
10) The actuator is snapped onto the rod which goes down to open the door. This rod just snaps off easily. You can now remove the actuator.
11) You'll see where the "plunger" pin has broken. This can be reglued and screwed into place as described in the earlier post. Allow to cure overnight.
12) (Optional) since this is a fixed window and _shouldn't_ leak I filled the door with fiberglass insulation to help lower road noise. The improvement was minor but it is a cheap to do.
13) Attach the lock but leave the cover off for a few days to make sure that the repair holds.
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