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1996 S420
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48 Posts
Discussion Starter #1
Hi Folks,
My 96 S420 trunk latches but the assist isn't pulling the trunk down fully, so it rattles a bit.. Not the end of the world but annoying all the same. The assist works fine on the doors. The central vacuum pump is disconnected (are the door assist and central pump intertwined in any way? ), so the locks do not work.
Is there any way I can disable the assist so the trunk closes fully?
Many thanks!
Chris
 

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1995 mercedes S420
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228 Posts
Hi Folks,
My 96 S420 trunk latches but the assist isn't pulling the trunk down fully, so it rattles a bit.. Not the end of the world but annoying all the same. The assist works fine on the doors. The central vacuum pump is disconnected (are the door assist and central pump intertwined in any way? ), so the locks do not work.
Is there any way I can disable the assist so the trunk closes fully?
Many thanks!
Chris
on my 95 s420 i unplug fuse #8 or #9 in the trunk fuse box for few seconds and then it works fine for few times .
 

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Registered
1992 600 SEL x 3, 1998 E430, 2002 E320T 4matic, 1971 300SEL 3.5 project plus 4 more W108, etc
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765 Posts
Hi Folks,
My 96 S420 trunk latches but the assist isn't pulling the trunk down fully, so it rattles a bit.. Not the end of the world but annoying all the same. The assist works fine on the doors. The central vacuum pump is disconnected (are the door assist and central pump intertwined in any way? ), so the locks do not work.
Is there any way I can disable the assist so the trunk closes fully?
Many thanks!
Chris
Up on the inside of the trunk lid you will find a small red lever. Pull it into the "down" position and the trunk will then fully close.

You will have to do this every time though. No big thing. Once you know where to feel for it, it is easy enough. :thumbsup:
 

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99 S320 (Sold at 280,000 miles) 2010 S550, 2008 C300, 08 SLK
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437 Posts
Perhaps the close assist is doing it's job and the latch has just come loose (common).
To get to it, remove the black plastic trunk threshold piece (and the 8 fastners) and you can see the latch. There are two bolts holding it in place. Mine get loose every few years ads need tightening.
 

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Premium Member
1997 S600 (sold)
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4,660 Posts
Perhaps the close assist is doing it's job and the latch has just come loose (common).
To get to it, remove the black plastic trunk threshold piece (and the 8 fastners) and you can see the latch. There are two bolts holding it in place. Mine get loose every few years ads need tightening.
You don't have to remove the entire trunk lip trim piece. There are two plastic sliding pieces right at the trunk latch mechanism that cover the two 10 mm bolts that hold the latch. Slide off those covers and check the 10 mm bolts for tightness.

Brett
 

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Premium Member
1997 S600 (sold)
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4,660 Posts
If it isn't just that the trunk latch is loose...

Does the pump run when you close the trunk? If you can't tell, leave the trunk lid open, stick your head in the trunk, and rotate the trunk latch to the closed position with your thumb. Do you hear the pump run from the upper left side of the trunk?

If the pump does not run, pull fuse 9 in the trunk, wait several seconds, and reinstall. Test the pump again. If it still does not run, you should pull the pump out from behind the trunk liner, and disconnect the connector at the pump, and reinstall.

If the pump function is restored to the trunk by pulling the fuse or the connector, you need to try adjusting the pump's pressure shut-off switch, otherwise you will likely experience the same failure over and over. While pulling fuse 9 will always reset the pump, the same conditions the caused the failure still exist. Adjusting the pump will likely restore function for a very, very long time (8 years on my pump, and not one single failure).

Here's what you need to know:

v12uberalles.com

Go to the DIY articles page, and click on my closing assist write up.

Brett
 

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Registered
1996 S420
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48 Posts
Discussion Starter #8
If it isn't just that the trunk latch is loose...

Does the pump run when you close the trunk? If you can't tell, leave the trunk lid open, stick your head in the trunk, and rotate the trunk latch to the closed position with your thumb. Do you hear the pump run from the upper left side of the trunk?

If the pump does not run, pull fuse 9 in the trunk, wait several seconds, and reinstall. Test the pump again. If it still does not run, you should pull the pump out from behind the trunk liner, and disconnect the connector at the pump, and reinstall.

If the pump function is restored to the trunk by pulling the fuse or the connector, you need to try adjusting the pump's pressure shut-off switch, otherwise you will likely experience the same failure over and over. While pulling fuse 9 will always reset the pump, the same conditions the caused the failure still exist. Adjusting the pump will likely restore function for a very, very long time (8 years on my pump, and not one single failure).

Here's what you need to know:

v12uberalles.com

Go to the DIY articles page, and click on my closing assist write up.

Brett

Thanks everyone for your suggestions. I pulled fuse 9 (8 is empty) and also listened for the pump in the trunk after latching it, but to no avail. Next I'll try to access the pump itself and see what happens.
 

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1993 400 SEL
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1,056 Posts
you might need a new pump
The fact that the closing assist works on all the doors mean he does not need a new pump. He just need to either adjust the timeout on the pump or he has an air leak on the trunk line or sensor issue or need latch adjustment.
 

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88 Mercedes 300SEL/15 Hyundai Sonata/91 Cadillac DeVille/72 Caprice Estate/73 Pontiac Grand Ville
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540 Posts
My trunk closes fairly tight, but not as tight as it should be. My "soft closing" or whatever it is called does not work on my car any longer, but the doors close just fine like regular doors that I am accustomed to. ;)

The power locks do work however. I am assuming the trunk pull down not closing was part of the problem with the system that closes the doors.

My '95 Lincoln and '93 Cadillac have the electric pull down motors on the trunks and have never had any problems with those.
 

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1999 S420
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7 Posts
"on my 95 s420 i unplug fuse #8 or #9 in the trunk fuse box for few seconds and then it works fine for few times" - WASIMTIGER1

He has it exactly right! This is the same problem and solution I use. It must be due to a short in the harness.
I have a 99 S420 that my parents owned and based on their MB dealer records they spent $$$ trying to get this fixed with new pumps, hoses,etc. I can review and post the various 'fixes' from the dealer if you need. Dealer stated it "works" but after a few closes it stops. Pitiful.

My dad just pulled the fuse for me and it corrects itself. Now whenever it happens I employ the fuse puller method.
Take Care.
 

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Registered
1993 400 SEL
Joined
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1,056 Posts
"on my 95 s420 i unplug fuse #8 or #9 in the trunk fuse box for few seconds and then it works fine for few times" - WASIMTIGER1

He has it exactly right! This is the same problem and solution I use. It must be due to a short in the harness.
I have a 99 S420 that my parents owned and based on their MB dealer records they spent $$$ trying to get this fixed with new pumps, hoses,etc. I can review and post the various 'fixes' from the dealer if you need. Dealer stated it "works" but after a few closes it stops. Pitiful.

My dad just pulled the fuse for me and it corrects itself. Now whenever it happens I employ the fuse puller method.
Take Care.
Pulling the fuse only resets the pump so it will work again. It's a short term fix and not a long term fix to the root cause of the problem. The real problem will still need to be determined and resolved. (ie. fuse 9 removal and reinsert is not a long term fix).
 

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1997 S500 Coupe
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136 Posts
Wow... annoyingly enough, after reading this thread, 2 days later mine started doing that same thing... IT'S A CAR VIRUS!!! -__-... Pulling the 9 fuse works for me too, keeps working for 2 weeks or so and then goes out. What on earth could this be...?

In my case, before the fuse is pulled, I do not hear the pump working when I close the trunk. The doors work fine though. So from reading here, I read that it could be a sensor? Where is the sensor? and I did a latch adjustment, it catches perfectly, just doesn't know when to pull in.
 

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Premium Member
1997 S600 (sold)
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4,660 Posts
wkuwiz, chrono123: A near dissertation has been written on the closing assist pump. The initial version is posted on this forum in the knowledge base thread stickied at the top. For the most up-to-date version, see the article on www.v12uberalles.com. Click to the DIY section and scroll down to the closing assist pump article.

The problem you two are experiencing is likely a combination of a couple of things: 1. The typical weakening ability of the pump to generate pressure due to normal wear, and 2. minor leaks in the external lines to the trunk or internally inside the pump.

A long-term fix involving adjusting the shut-off pressure of the pump is clearly explained in the article.

Brett
 

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'95 S500 (sold), '97 E420
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250 Posts
On mine (S500) the trunk will not pull down, because the striker is locked in the closed position.
The Close assist pump and dashpot work fine. But, there is a second dashpot, operated from the (whatever you call it) the pump under the back seat. That dash pot is not working, possibly a hole in the diaphragm.
How this striker works is when the lid is latched, the close assist pump pulls the lid down. When it's pulled down all the way there will be an audible click. That click is the locking pawl, falling into place to lock the striker in the closed position, (without that the lid would just jump up and down against the latch).
Now something has to release the pawl when you open the trunk, so that the striker will move to the open position. That's where the second dashpot comes in. It operates with the retractable handle. The pump that operates the door locks serves that dashpot, and the retractable handle. In my case, the dashpot that un-locks the striker from the closed position, has quit working, and the striker is stuck in the closed position.
Yet the retractable handle still works fine. I bought the car that way, and someone had adjusted the latch to allow for easier closing of the trunk. (but it won't seal, that way)

You can check the operation, by opening the trunk, and with the trunk open, close the latch, the close assist pump should run, the striker on the trunk lid should move. Listen for air hissing (don't want to hear air hissing), check to see if the handle retracts. All these things should happen simultaneously.
do the door locks work?

Just some food for thought, and some insight as to the workings of the trunk latch/striker.
 

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1999 S420
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7 Posts
Trunk seems to be a bear!

Brett & LCM Lee - Thank you for the posting on Uberalles. I read it and am thoroughly impressed by the lengths you went through to corect these issues.
Having gone through the service records on the car the entire Pump, trunk assist, striker, and several electronic components were replaced by the MB dealer on two different warranty visits concerning the issue. I will bring these records, and your suggestions, to my MB mechanic later this month.
For now as I say, when the fuse is pulled and the pump reset, it works fine (let the sleeping dog lie).
I will tackle it after a front bushing replacement (which seems to have given way). She's a great car with only 93,500 miles on her.

Thank you again for all your contirbutions and seriously thorough work.
CW
 
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