My car sorted itself out?! (Vacuum problem)
 

Hi,

The past two days, my car's held vacuum very very well indeed.
I have not done anything to the vacuum system. All I did was rewire the radio, speakers, and remove a weird part that I thought was useless.... (A long metal plate with a lot of holes behind the cigar lighter)

I lowered the idle, readjusted the rack damper, fixed the air filter, and that's it I think.

I was really surprised, because when I went just to check on the car yesterday the locks unlocked so quickly. The car even had enough vacuum that I could lock 'em again and open 'em all up again. (Everything including trunk and fuel filler door) - I did not start the car at all.

I was also surprised that there was no sign of water inside the car, where it leaked before... I did clean some of the drains though.

I hope it's not a coincidence. However the temperature did drop from 92F to about 39F in the past few days. Last time it decided to not work, there was the same coincidence.

I don't understand. Could one of the diaphrams just sealed itself or something? Maybe I had a valve that was stuck before?

Could the vacuum check valve contribute to this? I have also used the A/C a lot lately.....

just thought I'd share. Any thoughts would be great.

BTW, does anyone know if there's a vacuum element under each front seats in the W123C?

Have a nice day,

Holson Adi,

In my experience no part of a car heals itself. It is possible that a part exhibits the response of a failed part under only certain conditions, until it fails completely, which happens eventually. Additionally, a system made of numerous parts can exhibit peculiar behaviour based on the number of parts showing failed part responses, especially when they only exhibit the failed part response intermittently (under certain conditions) which makes figuring out what is going on even more frustrating. Eventually, however, a failing part will reliably not work and will consistently give a failed part response.

My read on your situation is a temporary combination of circumstances is helping some failing parts hang in there a little longer. Wait a little while and they will be reliably shot.

Good luck, Jim

I had a similar problem that seems to re-occur after several months. The problem for me is the driver door lock module. Seems to be the most worked vacume valve in the vehicle.

I just remove the door panel, access the module and wipe a thin film of o-ring lubricant (like vaseline) on the lock shaft. Vacume usually holds for several open/close tries, or until the resevior runs out of vacume. Just after I serviced it last, I left the car at the airport for 4 days. No problem.

Good Luck.

Jim Stevens

1985 300DT

hhm, I might try that.
I did replace the master vacuum switch too.. but, I'll do that since I have to take the door panel apart this weekend anyway.

I'm still wondering about the vacuum elements below the seats

I believe, but could be wrong, that the vacuum elements under the seats are to lock the seat backs in position when the doors are closed.

Yeah, the reason why I suspected one of 'em. The passenger side especially is because it doesn't really work. It needs to be helped (I've found where the linkage is) for it to close. It opens fine though...

Strangely enough, since I had to replace one of the 5 changeover valves under the dash, my car loses vacuum over night only if I leave the air on cold. If I turn it to heat or turn the system off altogether, it holds full vacuum pressure overnight. Before I replaced the valve, there was no problem whatsoever. Opened a can of worms perhaps?

Ok here is my contribution to Unsolved MBZ Mysteries: For years and years my 300td turbo burned about 1 qt every 1000 miles. Despite wringing of hands and frequent (every 2000 oil changes delo 400) service . All this time the hydro pneumatic suspension in the rear (accumulators and leveling valve) were shot and the fluid was like tar. The rear of the wagon was low and dragged coming up the driveway. My teeth knocked and head hit the headliner on bumps. No tech ever explained this to me. Then I finally became enlightened, logged on to this website, understood and fixed the suspension and cleaned the hydro fluid system. The car rides like a limo ...back end nice and high ..and I have not burned a drop of oil in 2000 miles! Also the transmission started shifting smoothly like it never has. This is after countless techs told me I had an unfixable blow-by problem and I shoulkd dump the car. Twilight Zone or MBZ magic? Now that I know the rings and valves aren't bad I am proceeding to tune the turbo and ALDA and discovering the car I had for years that I did not know I had. I was only able to do this because of the info on this site. The techs in my area have no idea how to fix esoteric old diesel maladies...I don't blame them... there is no money in knowing all this weird difficult old stuff for cars that have almost no market value

Well my car has held vacuum really well now. It hasn't failed to hold vacuum for more than a week now. However, there is one thing that I started doing that I don't think I did before. That is switch the A/C off.. that might have something to do with it.

The bane of Mercedes vacuum problems...
 

I have had vacuum problems like you are experiencing. In my experience, although surely any vacuum unit in the car can and does fail, the worst culprits are the bellows on the vacuum actuated door locks in the doors and trunk. The bellows tend to split after a few years, especially in a dry climate. My local MB dealer wants upwards of $90 for these simple units and refused to stand behind the unit when he sold me a faulty one. Over the years I have developed a repair that has worked well for me.

First, buy a pair of rubber gloves with small fingers. The yellow kind that people use for washing dishes has served admirably. Proceed to cut the fingers off the gloves and cut the tips from the fingers. Place the resulting tube over the vacuum bellows and squeeze it air tight by twisting a small wire around it above and below the bellows to form an air tight seal. The bellows then works like new (if you got a good seal). So far I've done several doors and the trunk on my MB. It's been several years...so far, so good. This little trick worked for me. Hope it helps you when you find your leaker.

P.S.: Sometimes the leaking bellows peculiarly seem to heal themselves for awhile and then start leaking again...just a matter of time. Best of luck!

thanks for the tip!
I'll keep that in mind when I find more vacuum elements.

I'm trying to see if I can reach the seatback vacuum elements... However, I can't really find a culprit now that it works. I do have a feeling that it could also be one of the A/C vacuum elements...

The other vacuum elements have been replaced w/ new parts...
$20 each.. what a waste of money... all of 'em were good when I took them off

Well I go with Holsons suggestion for now and switch the ac unit off at night. No more problems. I intend to finish rebuilding the entire vacuum system throughout the summer. I am about 1/3 done now and this is the only glitch. I will just keep replacing elements and hoses little by little.