Back-Up Assist Malfunction on '95 W140 LWB, Any Advice?

Door locks and assist

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My 1992 S320 has vacuum door but it doesnt work, Ive tracked a leak down to the lumber bags which Ive fitted new ones (£26 each). Does any one know where the resiviour is, as I need to trace the air line back to its sourse. Im sure the other end has come off as well. Does any one have a manual for this car?

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I have a 92 300 SE which has the vaccum assist which I just replaced the pump on. It is in the trunk on the left side next to the gas tank. It is very easy to replace. It's cost is about $198.00 US currency rebuilt from George Murphy (email address) [email protected] the door locks and truck handle pump is located under the rear seat on the right side of the car. This one costs about$400.00 US currency from George and is new. Good luck with these issues. I fixed both of mine this past weekend and glad that I did. The door locks and lumbar are on the same pump. Door and truck closers are on the other pump.

Locking pump

I had the closing assist in the trunk go twice, I screamed and they replaced it under "cusomer satisfaction" The fuses in the trunk usually have to do with the "closing assist" doors and trunk. The pump under the seat is for locking, the back up assist, headrests in some, vacum assist for the heat/ac, and i think the seat bolsters. I dont know where the fuse is (knock on wood)and hope I dont have to search for it. The pump uns untill it sees vacum or pressue build up, which would indicate all the diaphrams are pulled in or out. If it does not see this condition in some (10sec or so)it shuts off assuming there is a leak. This where the issue of a defective hose comes from and a bulletin from MB to open the pump and replace. I guess if the motor does not run there is another issue. It is in a foam rubber container and pretty quiet lift up your rear seat and investigate

Here is the story so far......

About 3 months ago I noticed later that the lumbar support didn’t feel right and my seats felt saggy, I tried to adjust my support and the system didn’t respond. This was also the case with the front passenger seat.
In the winter (about two months ago) in exceptionally cold snowy weather, the central locking system died in my car.
I could unlock the doors individually with a key.
I assumed it was likely a fuse had blown and didn’t think too much of it.
Later that day I opened my trunk and the handled (very slowly) popped out and didn’t return when closing the lid. On further investigation I noticed that my parking aides no longer popped up when reversing and my headrest down function didn’t work.

I disconnected the battery for about 10 minutes and tried again. The locks started working for about 10 seconds and then died again. I could still hear the relays clicking beneath the rear bench, but no action.

I lifted the back seat to access the pump unit. All hoses/connections appeared fine and intact.
I carefully, labeled all the hoses and then disconnected them one at a time.

I started the car and connected the live hissing hose by hand to each of the lines. All devices operated with connection and I was able to 'down' my headrests, 'in' the trunk handle the by connecting the appropriate hoses.

This means there is no leak in the hoses and the engine is still supplying the vacuum.
The clicking of the relays also suggests that the controls are still working and current is being sent to the pump.

I removed the pump, opened it and examined the insides. There was a red coloured hose with looked worse for wear so I tried to replace it with a new vacuum hose (a small piece of windscreen washer hose) which fit snug and well. While the unit was open I examined the PCB for breaks in the solder and wiring which may have occurred due to fatigue. I also took it on myself to clean the contacts in the vacuum micro switches with spirits. I then reassembled the unit, reconnected the hoses and tried again.

No joy. I reckon the pump has had it. I am now faced with buying a new pump. Does anyone know much these units sell for? and what are the options/costs for getting a rebuilt unit/ or one from a breaker.

I don’t know of any supplier other than the main dealer.

I am open to all suggestions and help you may have to offer

140

Here goes, you confirmed that all your devices are working, but did you ever get any noise or activity from the vacum pump? The pump supplies either vacum or pressure depending on which way the motor turns. While you have it out, and connected operate the headrests or lumbar, listen for it to whine. There was a bulletin from MB and it addressed defective (red hoses) which can be had from your dealer. but if there is no attempt to start there is a "relay" issue which causes the motor not to run. If it does run and shuts down there is a timing circuit, if it can not build up pressure or vacum. I dont recall but pricing is in the $300-400 and dont know of any other sources, purchasing from a dismantler could get you into another set of problems. There was a post from someone who went that route and got one that was not identical, there were two versions for my 92, and i would think the same applies to your year.

thanks for the speedy response...

Hi again Peter,

When the device is activated, I can hear the relays clicking. I do not hear the familiar whine from the pump - hence it's not starting.

I dont think its the red hose, I've already tried replacing it.

As per your suggestion I'll steer clear of breakers and contact the dealer on Thursday to find out the price of the pump

By the way my car is a 1994 LWB S320 - now developed transmission problems (flaring between gears / hesistant to upshift) ...SIGH...

Ouch...

Hi again Peter,

When the device is activated, I can hear the relays clicking. I do not hear the familiar whine from the pump - hence it's not starting.

I dont think its the red hose, I've already tried replacing it.

As per your suggestion I'll steer clear of breakers and contact the dealer on Thursday to find out the price of the pump

By the way my car is a 1994 LWB S320 - now developed transmission problems (flaring between gears / hesistant to upshift) ...SIGH...

Click to expand...

I just called some suppliers of Merc parts, here's the responses

Eurocarparts - We dont do that part
German and Swedish - We do vacuum pumps for just about every other model for about £90+vat apart from the W140 S class
Mercedes Benz main stealer - Part has to be ordered in from germany. To supply only it will cost £412.34+vat

For those of you in the states, vat is value added tax 17.5%

OUCH!!!....I am at the end of my tether, I am going to try and fix the old one again!!! [xx(]

Mmmm...I wonder if I can buy the one for £90+vat and use common parts to re-build my own one [?]