I think my closing assist pumps have had an average life of FIVE years, my first one quit right after my warranty ran out. I learned the #9 fuse trick but finally got tired of it, paid my $800 and had the pump replaced. The trunk was acting up afterward, so they replaced the lock with the 93/94 service bulletin which made the striker come out faster (Aug97). Approximately FIVE years later it started again, I went back to MB and complained, since I had almost every issue with my 99ML, they good willed a new pump under the condition that nothing else was found to be wrong. (Nov 2001). At about FIVE years, a month ago, it was acting up again, I had been reading all the posts and can only praise Brett Allison for his write up, and the input from others. I did not want to take mine apart, so I checked prices for a rebuilt and new pump, from a low of $270 plus $100 core, to a high from MB of $1150, my local dealer offered a 10% discount, Caliber 20% and I also found a new HELLA pump for about $400.
After reading Bretts article I tackled it. I have seen it done but have never done it.
First remove the tail lampsand liners on both sides, remove the rivets that hold them, also remove the liner over the gas tank and the speaker trim rings in the trunk. There are probably 20/25 of those plastic rivets put them in a container, then remove the liners. You will see the pump it is behind the bose amp, between the wheel well and the gas tank, unless you have yours mounted on the side I think this applies up to 95. The bose comes out, there is a latch on the connector which pivots up, take your time not to force anything. The pump itself is in a foam enclosure which resides in a plastic frame that slides into a metal bracket. carefully remove the foam encosure and remove the pump. There are 6 lines going to it plus a power plug, take caution when removing the lines from the nipples on the pump. I used a tool that is used to remove door panel retainers, a kind of two pronged fork that you can use to gently pry up. I would make sure the hoses (all red) are labelled.
So here I am looking at it thanks to Brett, and off to th bench we go.
There are four large torx at the top, and two smaller next to the electrical connector. The plastic cover snaps on to the bottom with 16 or so tabs once you get one the rest seem easy, insert a small knife in the seam while pushing down gently on a nipple in the area. I would work your way all the way around and the cover comes off.
The older pumps had a plunger with a nut, my newer, had a very small screw with a solder lug attached to the screw. There is a bar that is pushed against the screw by a diaphram to shut off the pump. I found my jewelers screw driver and gave the screw one rotation being carefull with the wire as you rotate it, so the wire does not break. I carefully alinged all the studs and slid the cover back on and after seeing all the tabs in place replaced the torx by feeling them catch (going backwards a half turn or so) and then snugged them down. The rest is just the reverse of what you did to get it out. Three days later not a miss, I wonder how many pumps have been replaced for this reason.
Thanks again, to Bret and all the contributors.
PS I did remove the trunk lid latch and checked it with my "mighty vac" before attacking the pump. The pump rovide pressure to close the doors, then sends vacuum down the line to reset the diaphrams, and from the merceds DVD, runs occasionally for 2.5 seconds just to keep the lines dry, twice every five minutes and then every ten minutes that was an uknown to me! (72-260)
If your adjustment is good enough, i.e. your pump runs for 2-4 seconds after you hear the door latch click, you will have many years more service from your pump... of course, that's as long as no major leaks develop. I'm sure that thousands of perfectly good pumps have been replaced, and that the "rebuild" that some organizations do consists of simply turning the adjustment screw. Nice profit margin to be sure. I should have gone into business turning screws instead of making this public.
Glad it worked for you. Please report any problems.
Thanks Bret, I studied your info multiple times, and finally said what the heck! I had the old pump around for a long time but threw it out many years ago.
If your adjustment is good enough, i.e. your pump runs for 2-4 seconds after you hear the door latch click, you will have many years more service from your pump... of course, that's as long as no major leaks develop. I'm sure that thousands of perfectly good pumps have been replaced, and that the "rebuild" that some organizations do consists of simply turning the adjustment screw. Nice profit margin to be sure. I should have gone into business turning screws instead of making this public.
Glad it worked for you. Please report any problems.
Brett
Has been working perfectly for me too in more than a year now.
I do believe though, that the original reason is, that the pump doesn't have the capacity it used to. But I also believe, that you can continue to do the trick until it can't close the doors anymore.
Has been working perfectly for me too in more than a year now.
I do believe though, that the original reason is, that the pump doesn't have the capacity it used to. But I also believe, that you can continue to do the trick until it can't close the doors anymore.
Yeah, it probably is a combination of slow wearing of the pump head and minor leaks developing in the actuator pistons that decrease the pump's ability to develop pressure. But, you only need enough pressure to close the door. As long as door latching occurs fast (within 1-1.5 seconds), the pump is providing plenty of pressure. This is the first thing to evaluate in my opinion. For some reason, it seems the factory spec calls for the pump to develop really high pressure. Because of that, it doesn't take much wear or minor leakage to drop below that. But, the doors will close well-below the factory specified max pressure set-point. I suppose the engineers wanted the doors to still close even if the latch became very sticky or difficult to close for other reasons (either some rich fat guy leaning against the door or maybe the body of a mafia hit wrapped in a rug ).
And, yeah, no reason you can't open it up again in 5 years and adjust lower once again... as long as the doors still close.
Linear Mode
