S-Class (W220) 1999-2006: S 320 CDI, S 320, S430, S 500, S 600

Help with Hydraulic Trunk Assist?

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Old 02-28-2017, 08:19 PM
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Help with Hydraulic Trunk Assist?

Hello everybody, I am having some issues with the power trunk on my 03 S600. When I bought the car, the trunk worked perfectly fine as it should. Sometime later, the power hydraulic assist failed and the gas struts were also shot, meaning the trunk would always slam shut if not supported with my hands and I would have to always hold it up when using it (it also weighs like 5000 pounds).

I started off by changing out the gas struts, and now the trunk holds itself like normal. Then, I moved onto the pump. I checked the fluid reservoir and, alas, it was empty. So I went and bought some Pentosin CHF 11s and filled the reservoir accordingly to a useful thread I saw. Here is where I started having some trouble.

Once I filled the reservoir with fluid, I shut the trunk manually and went inside to do a trunk reset (holding the button for 3 seconds). After everything was theoretically good to go, I tried opening the trunk. Nothing happened. The pump didn't lift the trunk.

So I was disappointed at first, but when I tried pressing the button to close the trunk, it actually worked! It also lowered that pesky right hinge on the trunk that always sticks out on every single W220! So at that point, I was trying to figure out why it would only work whenever its closed and not opened.

After troubleshooting a bit and closing it a few times with the power assist, I start to notice a seeping sound from the area where the pump lays. I open it up, and I notice that the brand new fluid I just put in is leaking out! I take apart the side trunk panel, and find that the leak is coming from one of the hydraulic lines and not the pump itself, luckily saving me the cost of a new pump (I think). I just disconnected the pump from its electrical plug for now until I can figure things out.

So here is where I come in asking for help. My pump works fine, and sounds completely healthy when it was running. I don't want to pay a ridiculous price for a new pump when all I need are some new hydraulic lines. Is there any place I can take the pump assembly to just so they can repair only the hydraulic lines? Also, what caused my trunk to close with the power assist but not open with it? My vacuum trunk latch seems to be working fine, so I assume it has nothing to do with that. Any help here is appreciated guys, thank you.
Old 02-28-2017, 10:42 PM
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How much did you fill the pump reservoir?
With the trunk lid open, the fluid level should be in the center (bulls eye) of the plastic reservoir. As this is a "run-around" system, the level will go up on lid closing. If you overfilled it, it has to come out somewhere.

You an check my nick on the proper filling on both forums.
Good luck!
Old 03-01-2017, 12:20 AM
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www.tophydraulicsinc.com

Klaus is a great guy and they have a cylinder rebuild service only. My CL needs it. You can also send in the whole unit and get it built better than new for way less than what MB wants for a replacement.

I don't understand why you can't order just the ram separately, they are usually all that leaks.
Old 03-01-2017, 12:21 AM
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Originally Posted by kraut56
How much did you fill the pump reservoir?
With the trunk lid open, the fluid level should be in the center (bulls eye) of the plastic reservoir. As this is a "run-around" system, the level will go up on lid closing. If you overfilled it, it has to come out somewhere.

You an check my nick on the proper filling on both forums.
Good luck!
I filled the fluid at the proper level, right at the center while the trunk was open. One of the hydraulic lines connecting the pump to the hydraulic cylinder was ruptured, so the fluid leaked out. Can I replace the line somehow? The ends that connect to the pump is tied on with a hex nut, so that side is removable. However, the end that connects to the hydraulic cylinder seem to be fixed with the lines. Will certain hardware stores repair it if I bring just the lines and the cylinder without the pump?
Old 03-01-2017, 01:07 AM
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Any good forklift repair /hydraulic repair shop can do it

Or buy a used one on eBay
Old 03-04-2017, 05:21 PM
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I'm going to get the lines repaired soon, but I'm still unsure as to why the trunk doesn't open with the hydraulic assist, it only works when you go to close it. The trunk latch pops the trunk immediately when it the open button is pressed, but the hydraulic pump does not lift the trunk. Any idea for why it's doing this?
Old 03-04-2017, 05:48 PM
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I'm guessing a wire has broken contact , mine does the opposite , it will lift hydraulically but will not close

The hydraulic pump isn't receiving the electrical signal to run the opposite way so it must be a wiring connection issue
Old 03-04-2017, 06:39 PM
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That may be it, I'll check and see if there is any electrical signal to the pump when opening the lid. Also, how do I remove the hydraulic cylinder that is attached to the lines and the pump? The lines that are attached to the pump can easily be removed with a hex screwdriver, but I'm having trouble figuring out how the other end that is attached to the cylinder comes off. There seems to be a locking clip over one end of the cylinder (similar to the gas struts that hold the trunk), but I'm not sure how to remove the other end or the cylinder as a whole.
Old 03-20-2017, 03:33 PM
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So I am at a roadblock here, and hope someone could help me out because I can't find any information regarding this...

I can't find a way to remove the hydraulic cylinder from the trunk. One side of the cylinder has a clip on it, but when I tried removing that it didn't help much. I looked at pictures of the whole assembly removed from the car on ebay, and each end looks to be held in place maybe by a ball joint? See what I mean below:

http://www.ebay.com/itm/00-06-W220-M...dYyC~X&vxp=mtr

I tried pulling on each end with a significant amount of force, without trying to break anything, and had no result. I attached pictures so people can better help understand my situation, and also the torn hydraulic line that I wish to repair. Any help regarding how to remove this would be really appreciated, thanks.








Last edited by AlexMercedes; 03-20-2017 at 03:39 PM.
Old 03-21-2017, 05:13 PM
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Remove the circlip (black retainer) The ball can get seized in the socket and will require some loving force to extract.
Old 03-22-2017, 01:12 AM
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I've finally gotten the damn thing out. Was stuck, had to use "quite" a bit of force to get it out. And yes, it is held in by a ball and socket. I'm going to go get the lines repaired and will come back with an update.
Old 05-05-2017, 12:06 PM
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Have you solved the problem?
Old 05-05-2017, 04:44 PM
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my S600 went to a lot of problems with this. First I had a battery failure, I put the car in storage, and this spring installed a new battery and took the car home. The trunk had no action whatsoever, I had to open it with the mechanical key.

Hooked up DAS, and it gave me a rather implausible fault of trunk angle sensor shorted to ground or battery plus.

cleared the fault, and the trunk promptly unlocked with the fob, but did not lift.
fluid was low (after five years), refilled it and cycled it several times and refilled it again.
All is good now!
Old 05-08-2017, 03:21 PM
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I have a similar problem that I just noticed yesterday. I'm sort of thinking mine must have a leaking hose. The pump has fluid, new shocks installed less than 4 months ago, and if I push the button on the trunk or door it will pop open but not lift up or close. Might be time to start pulling back that covering for further investigation.

Why couldn't Mercedes just make a trunk like everyone else?
Old 05-08-2017, 07:14 PM
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good question, but no clear answer. Even the simple electrical system on my E350 is crapping out for the second time in 8 years.

If you pull back the covering, you'll probably find some seepage, but that is easily replaced. I found that forcibly closing the trunk would produce a lot of foam in the reservoir. subsequent refilling and cycling then fixed all the problems.
Old 05-09-2017, 03:54 AM
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I just pulled out the whole unit for now until I get it repaired later since I'm dealing with another issue right now. Any hydraulic repair shop can do it, and for rather cheap. Yes, it will be quite messy down there in the battery compartment if you think you have a leak.
Old 05-21-2017, 08:50 AM
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Update

Originally Posted by kraut56
my S600 went to a lot of problems with this. First I had a battery failure, I put the car in storage, and this spring installed a new battery and took the car home. The trunk had no action whatsoever, I had to open it with the mechanical key.

Hooked up DAS, and it gave me a rather implausible fault of trunk angle sensor shorted to ground or battery plus.

cleared the fault, and the trunk promptly unlocked with the fob, but did not lift.
fluid was low (after five years), refilled it and cycled it several times and refilled it again.
All is good now!
Since with during the battery reinstallation the trunk lid kept falling down on my head, my friend was tasked to hold it up (tough job!).

Ordered 2 new gas springs (left and right are different part#), and installing them took about 5 minutes - use the new ones to identify where to insert a small flat blade screw driver to release the black safety clip, you do not need to remove it).

The old ones were manufacturing dated 2007 and 2008, so they were NOT original, and that indicates a service life of about 5 - 7 years.

The old ones could be compressed easily by hand. the new ones not.
This seems to really ease the work load on the pump, which runs very silently now.

FYI
Old 05-21-2017, 05:26 PM
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Yeah having good struts is very important, they carry the weight. The hydraulics is just there to open and close, not support it, and it's a HEAVY trunk without the assist springs from the non-power models.

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