Closing assist pump and Central lock pump trouble

[alex54]

After I seen few discussions over how-to-fix the closing assist pump I decided to pull mine off and work on it. First off, pump would work for few times before times off, then reset fuse #9 brings it back to life…After I had the pump out on trunk floor and removed air lines, I noticed a couple of small chips broken out of nozzle HD and SK…I tried to use and wrap the chip with water pipe sealant -Teflon Tape- as Brett advised in previous post, and retest it after connecting the other air lines to it, that didn’t seem to go anywhere, pump would still run for around 10 sec and times out after few tries, I have attached some pictures for clarification…
Plus I have trouble with the central lock pump (located under the back seat); it does lock the rear doors but not the front (driver and passenger) doors.
Any help or input would be appreciated.

[Peter Guenther]

You seem to have two issues, one is the closing assist pump, which evidently has been worked on by someone who chipped the port nipples. The isuue is the pump has two functions, one is to shutoff when the diaphram contact is interrupted. The second is a timeout if it runs longer than 10 seconds. see article

V12 Uber Alles, Getting to know your Closing Assist Pump in a W140 Mercedes Benz, an article by Brett Allison

The second is your locking pump your locking pump seems to have a leak in the lines since the doors all share the same source, it is pressure to unlock and vacuum to lock. This pump also provides pressure for the lumbars and vacuum for the HVAC when the engine does not in two seperate reservoirs, and also has a timeout function. If the rear doors function, look for a leak or obstruction in the front door line, and dont forget it also services the fuel door and trunk lock.
There is a tool called the Mighty-Vac which allows you to draw a vacuum and a guage to see if it leaks down

[AlexanderZwo]

Concerning the softclose: after your attempt with the teflon tape, does pump still loose pressure at the chipped nozzles?

Concerning front doors: Can be in the lines or in the actuators in the doors...listen for a hissing sound and locate the leaks...

Best regards
Hubert

P.S.: That was quite simultaneous, Peter....

[alex54]

After I taped the chipped nozzles, pump still lost pressure and failed after few tires, but this time not from the chipped nozzles, not sure what to look for next!
Concerning the central lock pump, do you guys think a new pump would solve the problem or it sounds like leak issue since everything work except the front doors? Thanks

[Brett San Diego]

Regarding the closing assist pump:

Don't worry about the SK line. It is only a pump exhaust line. It doesn't have to hold pressure.

The steps to take are fairly clearly outlined in my article. First, confirm that your pump runs, which yours does. Second, confirm that the pressure shut-off switch is functioning properly. Third, check each line for major leaks and fix them if you find any. And fourth, adjust the pressure shut-off switch. You can skip #3 and try #4 first and see if the systems runs fine after adjusting. If it does, you can probably conclude that there are no major leaks.

Good luck,
Brett

[AlexanderZwo]

Originally Posted by alex54

... or it sounds like leak issue since everything work except the front doors? Thanks

I assume it's a leak issue, but it can be electrical as well... But probably it's not the pump itself.

Best regards
Hubert

[alex54]

Thanks guys for your input...I will try to follow Brett steps and post results when done.

[Johnnay]

Is the closing assist standard or an option? I just got a 92 500SEL, and after reading this I dug into my trunk only to find there was no pump... or did the PO just take it out when it failed?

[AlexanderZwo]

I think it depends where you are. In Europe it was an option. In the States it was standard I think.

Check the nose at the lock of your trunk hood. Is it a "mechanism nose", then the car should have a softclose. Is it just a nose bolted to the hood, then not.

Best regards
HUbert

[Peter Guenther]

All US 140s 92 and up had close assist, the pump is way back there between the gas tank and wheel housing, in a foam housing there should be 6 hoses with labels on them!