Trying to track down those pesky leaks... - PeachParts Mercedes-Benz Forum

Tomguy · #1 12-18-2002, 04:13 PM

Well, I'm working on my pneumatic lock system. I'm taking all the door panels off and replacing the fittings that hold the hose on to the vacuum element. My question is: Is there one spot where the system usually leaks or is it just guesswork? I'm looking at the diagram right now and it does look to be a pain if the hoses themselves are actually leaking. Has anyone got experience in this area?
Pardon the poor quality, I don't have my scanner handy.

gmask · #2 12-18-2002, 05:07 PM

My neighbor had a similiar problem on a 80's mb sedan and it seemed to be that he just had to trace the whole system. There could be numerous leaks. It was also complicated by a botched repair job that the previous owner had attempted.

Tomguy · #3 12-18-2002, 07:28 PM

I know I dont have #51 (there are two on the page, so I'll be specific - the one in the driver's door), but I have 3 short hoses there instead. Also, my air tank is different than the picture. Is it possible that someone attempted to repair my system in the past? It DID work about 6 years ago...

MikeTangas · #4 12-18-2002, 09:26 PM

Once you have all of the connectors replaced you will need to test each actuator individually. Test both the lock and unlock sides of the diaphrams. You could very well have a whole bunch of small leaks contributing.

I've found, at least on the 108, that most often it is one of the upper diaphrams that is shot. Remember, the actuators, even though inside the door, are still exposed to the elements. Grit and dirt wear at the rubber, while air, heat and cold do their thing too. If you use a mighty-vac you should be able to isolate and test each side of the actuators and verify good/bad.

One other thing to check, I found on the passenger side, sometimes the down limiter gets slightly bent, allowing the bottom of the glass to make slight contact with the upper diaphram, slowly rubbing a hole in it.

If all else checks out, last place to check is the hard lines where the pass fromt the door jamb to the door. Constant opening/closing takes it's toll there as well.

Not sure what your vacuum resevoir looks like, on teh 108 mine looks like about 12 tennis balls connected. Once I removed it from the left front fender to test for leaks, it still looked factory new, but dusty. Heavy duty material that will probably never wear out.

I just looked and notice we're discussing a 108, so everything I have is pertinent. One last note, the 108's are one of the last cars to have rebuildable actuators. If you can find the rubbers you can rebuild. Rubbers cost about $6 each, complete actuator units about $50.

Tomguy · #5 12-18-2002, 11:36 PM

Mine was 15 tennis-balls, looked nothing like the parts catalog

Where can I find those peksy rubbers? All I can find are stores out of the actuators >_<. I siliconed the one for my trunk and it seems good now, the others dont seem to leak (or at least not much) but I have yet to check the front pass door. It's the only one that doesnt lock when I suck on the line (sorry, no vac pump here >_<). But NONE unlock... and they dont leak.

MikeTangas · #6 12-19-2002, 12:34 AM

First off you really should get a mighty-vac, really helps when troubleshooting the system.

When you say none unlock, do you mean with the key, or when you manually lift the driver's lock knob from inside? If it is with the key only, that might not be a vacuum related problem. There is a small kidney shaped piece in the lock mechanism that likes to break, unfortunately that piece cannot be obtained separately (at least that I couldn't get one). I did find that there is also a small set/adjustment screw which moves the business end of the mechanism a little closer to the lockworks, adjusting this screw allowed the parts to mesh and the lock functioned normally again.

If none unlock when lifting the knob, then we're on vacuum related ground. Using your newly purchased mighty-vac, you can check function at the master valve in the driver's door. The yellow line is the main vac feed, the other two are for lock and unlock (can't remember which color is which right now). Test them both. If none unlock from this point, then you have a major vacuum leak and you'll have to track it down.

Remember, vacuum leaks do cause poor running conditions, and having a leak in this system will cause lower than optimal manifold vacuum (that;s where the vac is drawn from). Don't forget to check out the check valve in the main line between the manifold and first split. those often go bad and you'll hold no vacuum at all.

240 Ed · #7 12-19-2002, 06:08 AM

Right on Mike!

Tomguy, you are fortunate to get this wonderful info on your car from Mike!

and, you cannot generate enough suction with your mouth as you need,

MityVac is worth the money, believe me!

gmask · #8 12-19-2002, 12:12 PM

Quote:

Originally posted by 240 Ed
MityVac is worth the money, believe me!

Oh yea I forgot to mention that my neighbor went through two cheap vaccuum pumps before buying a decent one.. could have been a mityvac but I don't remember.

Tomguy · #9 12-19-2002, 05:29 PM

Remember, the clear goes to the gas tank lock: The clear is lock, black is unlock. I can generate ample suction with my mouth to lock everything but the pass door, and I cannot unlock anything. My system DOES have ample vacuum once it starts running though

It has to run a bit though... I think that's cause there is a leak in the unlock system somewhere.

gmask · #10 12-19-2002, 05:32 PM

Quote:

Originally posted by Tomguy
Remember, the clear goes to the gas tank lock: The clear is lock, black is unlock. I can generate ample suction with my mouth to lock everything but the pass door, and I cannot unlock anything. My system DOES have ample vacuum once it starts running though It has to run a bit though... I think that's cause there is a leak in the unlock system somewhere.

Not the same will apply for you but I think one of the locks that leaked on my neighbors car was for the fuel door. He had to replace the diaphagm and the spring.

Tomguy · #11 12-19-2002, 05:55 PM

gmask: That was the first place I looked. It works fine, believe it or not. Not a pinhole leak even

Dammit, why can it never be the easy ones, why does it always have to be the hard ones and/or the last place you look :p

gmask · #12 12-19-2002, 05:56 PM

Quote:

Originally posted by Tomguy
gmask: That was the first place I looked. It works fine, believe it or not. Not a pinhole leak even Dammit, why can it never be the easy ones, why does it always have to be the hard ones and/or the last place you look :p

it's allways the last place you look ;-)

Tomguy · #13 12-19-2002, 06:09 PM

Unfortunatley, gmask, you're right. Damn Murphy's law, why couldn't it be "The problem is always the first place you look"?

http://www.cpuidle.de/edition.htm

Tomguy · #14 01-01-2003, 07:47 PM

Just an update: I MIGHT have MOST of the leaks down. I took EVERY one of them out: They ALL leaked at the seams (of where the rubber met the plastic housing part). I sealed them all with Ultra Blue RTV silicone (which I couldn't find... they just had the regular blue, thankfully I had enough to finish!). I have the system on "Lock" now and I am going to let it sit overnight, if tomorrow the gas tank is still locked (since it needs a vacuum at all times to keep it locked) I'll be VERY happy!