regarding vacuum locks on 240d - PeachParts Mercedes-Benz Forum

CzarN · #1 06-25-2003, 01:57 AM

the vacuum (system?) controlled door locks on my '81 240d haven't worked in a long time. i've never bothered to figure out if it was the pump, or just a leak, or whatever. i'm the only one who rides in the vehicle 99.9% of the time so i just unlock the drivers door with the key.

well tonight i was rolling down the road coming back from work and i heard this hissing noise which i didn't recognize over the radio. which of course caused emergency sirens to go off in my head, but upon turning down the radio i found that it seemed to be coming from the seam where the driver's side door attaches to the frame. i noticed i had somehow managed to set my elbow or something on the little ... um .... the knob to lock the door. so i pulled it up and the hissing stopped. locked it again, more hissing.

i know exactly jack about vacuum controlled door locks. is the evidence i discovered tonight indicitive of anything in particular, and if so what would be necessary to fix it?

thanks,

--Nick

MS Fowler · #2 06-25-2003, 05:44 AM

Sounds like you might have found a leak in the system. Vacuum is carried in yellow colored hard lines. You can probably stop the leak by slipping a piece of soft rubber tubing over the break.
With all the check valves in the system, I do not believe a leak will affect other vacuum operations, like the auto trans shifting. Although a sufficient leak will cause the engine shut off to not work properly--thats a pain.

Rick Miley · #3 06-25-2003, 10:18 AM

You're not hurting anything by just leaving the lock up to stop the vacuum leak. But are you asking for help to fix the door locks? If so, get down to AutoZone and buy a MityVac for about $26 or so. Then come back here and we'll walk you through it. They're not difficult to fix.

Zoonhollis · #4 06-25-2003, 01:37 PM

Almost invariably, the first component to go south on these vac systems is the vacuum bellows assembly in 3 of the doors, the fuel door, and the trunk lock. The driver's door has a "master" vacuum actuator near the handle, and yours may be bad. An easy replacement...buy it new here or get one from the boneyard. I happen to have an extra that I will send you for free if you determine that it's the problem component.

JHZR2 · #5 07-01-2003, 10:09 AM

OK, I didnt start this thread, but Im going to piggyback onto it... I got a mityvac, and now would appreciate a bit of walkthrough in checking the locking system... My car will start and stop, shift, and lock/unlock fine when on or immediately after turnoff. However, wait more than 30 seconds, and I have next to no vacuum. Plus, lately if I dont lock my doors, the car will have trouble shutting off if I dont do a high rpm highway run. Around town is bad in that regard. Every once in a while my fuel filler door doesnt lock with everything else, so thats the first culprit. But Id like to know where to start looking. Is there some main connector that all the doors feed off of? Where is the location that will allow me to check all the lock actuators and their feed lines from?
Many thanks,

JMH

jfenn · #6 07-01-2003, 10:39 AM

I just went through this with my 1983 300 CD. There may be some slight differences but I think they are about the same. The first test that I did was to check the check valve, yellow, near the fire wall in the engine compartment that has two yellow hard plastic lines going through the fire wall. Take the check valve off and see if it working. Then with the mighty vac pull a vacuum on each line and see if they will hold. One of the lines goes to the reservoir which will take quite a bit of pumping before it has a good vacuum on it or if you can't pull a vacuum there may be a leak. (mine was fine) Do the same with the other yellow line which goes to the locks. (this would hold a vacuum when the locks were open and not when they were closed. Therefore, I assumed that it was on of the actuators, my gas flap lock had failed long ago so I suspected this was the culprit.)

I unplugged the gas flap actuator and plugged it off and the other locks worked better but it would still not hold a vacuum for more that 30 minutes. I then decided to buy actuators for all the other locks, (this was not too bad since I only have two doors). I replaced all the actuators including the gas flap and it works like a charm and holds a vacuum overnight. I don't know exactly which actuator was causing the slow leak and if you want to spend more time tracking each one, you can probably avoid buying all the actuators. I figured that I might as well replace them all.

If necessary you can access junctions in the vacuum lines underneath the carpeting on the front passenger side (at least on a 300 CD). I pulled my carpet but did not have to actually disconnect the lines to individually test each actuator. (the way mine were run made it look like it would be a bit difficult to disconnect, test and reconnect, so I opted to replace all actuators.)

Partial removal of the door panels was fairly easy. First remove all the hardware such as handles, chrome decorative plates and there is a plastic insert in the door handle that has to be removed to remove a larger screw. After all the hardware is removed, then with a flat screwdriver or I used a thin prybar, you just "pop" the holder clips directly out. (you may want to buy some new ones since they get brittle over 20 years and a few had to be replaced.) I did not have to completely remove the door panel to replace the door actuators. I tried but the clips that hold the panel on the top were bound too tight and I was afraid of breaking something and did not need to remove them entirely.

The trunk and gas flap actuators were fairly easy to replace as well. I also purchased a manual from **************.com which was very helpful in giving me the confidence to removing the door panel. You should also check out thomaspin's (he has several posts) web site which shows pictures and gives a great overview of removal of the door panel (as well as many other very helpful things relating to working on mercedes).

Hope the helps. I am sure that a search will also turn up several other helpful posts.

Rick Miley · #7 07-01-2003, 11:32 AM

Ok, here's some more stuff specific to the 240D.

First, the check valve is in the engine bay near the oil filter and has three lines on it. The side with the single port shoud go to the vacuum souce (the pump at the front of the engine). The side with two ports shoud go to two yellow lines that go through the firewall.

The check valve should allow air to pass from the two port side to the single port side. (The vacuum pump is sucking on it) It should also allow air to pass freely betwen the two ports that are on the same side. And it should NOT allow air to pass from the single port side to either of the ports on the two port side. To test that, plug one of the ports, put the MityVac on the other and pump it down. It should hold vacuum. Do NOT plug the single port side for this test - it should hold on its own.

Next, use the MityVac to pump down the yellow line with the gray stripe. This line runs through the cabin along the floor on the passenger's side to the vacuum reservior in the trunk under the package shelf. There are no breaks or branches in that line. It will take several pumps to develop vacuum in the reservoir because it holds a lot of air. But it should develop and then hold vacuum indefinitely.

Next, test the solid yellow line. It runs from the firewall to the lock actuater valve in the drivers door to supply vacuum for the rest of the locks. To test this line separately, remove the driver's door panel, remove the solid yellow line from the valve, and plug the end. Then pump down from the engine bay end with the MityVac. (This line was one of the problems in my car)

Next, test the rest of the vacuum lines. The vacuum runs through two sets of lines starting at the driver's door, and running to the other three doors, plus the fuel filler and the trunk. The yellow lines with the red stripe provide vacuum to lock. The ones with green stripes provide vacuum to unlock.

The routing is as follows: The lines run from the driver's door to a branch in the plastic channel under the carpet in the driver's footwell. From there, the lines going to the rear are for the rear driver's side door and nothing else. The lines running along the front edge of the seats supply everything else.

There is another branch in a similar location on the passenger's side floor. The red and green striped lines running forward supply the passenger's door and nothing else.

One set of lines running rearward is for the rear passenger's side door, and the other set is for the fuel filler and trunk.

The best thing to do is test each branch of the circuit with the MityVac to see if it will actuate and hold vacuum. Test both lock and unlock functions separately.

The fuel filler is different from the rest, as it only has the lock line connected to the vacuum pod. Unlocking is done by a spring. To access it you have to remove the plastic trunk liner panel.

The trunk lock vacuum pod is located behind a small access door near the lock in the trunk. The rubber diaphram on it is very thin, unlike the rest of the actuators, and looks easily torn or split. (This was another problem on my car)

Another possible vacuum problem, although not lock related, is the climate control system. That has at least two actuators that I know of under the dashboard near the console. Vacuum is supplied by the green line from the engine bay, through the compressor control knob, to the two pods. Yes, even the lowly 240D's "manual" system is partially dependent on vacuum. If there's a leak here, then it could cause all vacuum systems (locks and engine shutoff) to be weak.

You'll see that all the vacuum lines are joined by black rubber hoses. A great way to test the system is to plug the hoses with golf tees so you can pump down one branch at a time with the mityvac.

Good luck and happy hunting.

GottaDiesel · #8 11-04-2003, 07:08 PM

Quote:

Originally posted by Rick Miley
Ok, here's some more stuff specific to the 240D.

First, the check valve is in the engine bay near the oil filter and has three lines on it. The side with the single port shoud go to the vacuum souce (the pump at the front of the engine). The side with two ports shoud go to two yellow lines that go through the firewall.

The check valve should allow air to pass from the two port side to the single port side. (The vacuum pump is sucking on it) It should also allow air to pass freely betwen the two ports that are on the same side. And it should NOT allow air to pass from the single port side to either of the ports on the two port side. To test that, plug one of the ports, put the MityVac on the other and pump it down. It should hold vacuum. Do NOT plug the single port side for this test - it should hold on its own.

Next, use the MityVac to pump down the yellow line with the gray stripe. This line runs through the cabin along the floor on the passenger's side to the vacuum reservior in the trunk under the package shelf. There are no breaks or branches in that line. It will take several pumps to develop vacuum in the reservoir because it holds a lot of air. But it should develop and then hold vacuum indefinitely.

Next, test the solid yellow line. It runs from the firewall to the lock actuater valve in the drivers door to supply vacuum for the rest of the locks. To test this line separately, remove the driver's door panel, remove the solid yellow line from the valve, and plug the end. Then pump down from the engine bay end with the MityVac. (This line was one of the problems in my car)

Next, test the rest of the vacuum lines. The vacuum runs through two sets of lines starting at the driver's door, and running to the other three doors, plus the fuel filler and the trunk. The yellow lines with the red stripe provide vacuum to lock. The ones with green stripes provide vacuum to unlock.

The routing is as follows: The lines run from the driver's door to a branch in the plastic channel under the carpet in the driver's footwell. From there, the lines going to the rear are for the rear driver's side door and nothing else. The lines running along the front edge of the seats supply everything else.

There is another branch in a similar location on the passenger's side floor. The red and green striped lines running forward supply the passenger's door and nothing else.

One set of lines running rearward is for the rear passenger's side door, and the other set is for the fuel filler and trunk.

The best thing to do is test each branch of the circuit with the MityVac to see if it will actuate and hold vacuum. Test both lock and unlock functions separately.

The fuel filler is different from the rest, as it only has the lock line connected to the vacuum pod. Unlocking is done by a spring. To access it you have to remove the plastic trunk liner panel.

The trunk lock vacuum pod is located behind a small access door near the lock in the trunk. The rubber diaphram on it is very thin, unlike the rest of the actuators, and looks easily torn or split. (This was another problem on my car)

Another possible vacuum problem, although not lock related, is the climate control system. That has at least two actuators that I know of under the dashboard near the console. Vacuum is supplied by the green line from the engine bay, through the compressor control knob, to the two pods. Yes, even the lowly 240D's "manual" system is partially dependent on vacuum. If there's a leak here, then it could cause all vacuum systems (locks and engine shutoff) to be weak.

You'll see that all the vacuum lines are joined by black rubber hoses. A great way to test the system is to plug the hoses with golf tees so you can pump down one branch at a time with the mityvac.

Good luck and happy hunting.

This is awesome, and I think *VERY* worth bumping!

Thanks!