Vacuum help? - PeachParts Mercedes-Benz Forum

kerry · #1 01-01-2005, 04:17 PM

The locking mechanism had a vacuum leak on my 85 300td. I disconnected the door locking system under the hood and plugged the line a few months ago, now I'm trying to troubleshoot it. All the door pod mechanisms, including tailgate and fuel door test fine both opening and closing. On the switching valve on the drivers door there are three lines. I can pull a vacuum on the rear one and it locks all the doors. I can pull a vacuum on the center line but nothing happens. The center line holds vacuum. I can't pull a vacuum on the front hose to the switching valve. I also can't pull a vacuum on the hose going to the system from under the hood.
Is there any one with wisdom as to what is happening? I assume this means that there must be a leak somewhere between the line under the hood and the driver's door switching mechanisms. But, I'm assuming the center line on the switching valve is the unlocking line. Why won't the doors unlock when I pull a vacuum on that line? What am I missing here?

EDIT:
Now I'm more confused. I can still pull a vacuum on the rear most line of the driver's door switching valve but nothing happens. I've also looked at the sticky vacuum diagram and now know the middle line is the line from the vacuum pump. It still holds a vacuum so I know the line from under the hood to the driver's switch is good.
So, I'm concluding that my problem is a leaky unlocking line somewhere. Any hints as to where it might be? Where should I tap into the unlocking line downstream to test it?
But there is still the oddity as to why the doors wont lock when I pull a vacuum on the rear line at the driver's door switch. I also locked the driver's door and then pulled a vacuum on the system from under the hood at the locking mechanism line. I assumed this should lock the doors since the unlocking line should be excluded from the system by reason of the driver's door being locked. I could only get 10 inches of vacuum there (as opposed to 24(?) when I tapped into the locking line directly at the driver's door switch?
Any ideas? My mind is a vacuum.

kerry · #2 01-03-2005, 04:53 PM

TTT

ANyone have any ideas? I replaced the valve on the drivers's door. (by the way--the dealer says there is a new valve for that location--$51. I bought the old version for $18).
The unlock system won't hold vacuum so I know I have a leak there somewhere. But the locking side is still holding vacuum but non of the doors lock. Does anyone have any idea why this would be happening. They worked fine before the whole problem arose and they worked once when I pulled a vacuum on the locking hose on the driver's door switch. But now nothing happens either with a mity vac or with the system vacuum.

engatwork · #3 01-03-2005, 04:56 PM

Kerry - have you looked at the vacuum diaphragms for your particular model. They are "stuck" at the top of the diesel forum.

Fishslayer · #4 01-03-2005, 04:58 PM

I think the next "junction" down the line is in a plastic tray under the passenger floor mat. Should be a couple rubber 4-ways under there

kerry · #5 01-03-2005, 05:17 PM

Yes, I looked at the diagrams after my initial explorations so now have a rough idea of where the lines run.
I tested each of the diaphragms at each door and all worked fine isolated from the system.
The leak in the unlock side seems to be just a matter of tracing down a leaking connector somewhere.
But, for the life of me, I can't figure out why the doors aren't locking. There's no indication of any leaks anywhere on the locking side and it holds both with the system hooked up (car shuts off fine when in the locked mode) and holds vacuum with the mity vac but no movement at all on any of the locks.

mgt83300D · #6 01-03-2005, 05:28 PM

try using the mity vac on each door actuators. the rubber boot that seals the unlock side of the actuator diaphragm around the actuator shaft ALWAYS splits and leaks away your vacuum. as far as the locking problem, it sounds like you have a massive leak on the locking vacuum line either going across the floor to the passenger side of toward the back on the gas door/trunk line.

mgt83300D · #7 01-03-2005, 05:30 PM

... double check that you don't have any lines crossed at the driver door switch.

Fishslayer · #8 01-03-2005, 05:34 PM

Could be a kinked hard line- holds vac yet it cant pull the actuators, try opening and closing the dooes with the mityvac hooked up.

mgt83300D · #9 01-03-2005, 05:38 PM

http://www.**************.com/store/item.php?item=123%20Vacuum%20Door%20Lock%20Advanced%20Troubleshooting%20and%20Repair

try this site for some good parts and troubleshooting info. It helped me fix my llocks.

dmorrison · #10 01-03-2005, 07:22 PM

Kerry, I got carried away with my reply

Start at the begining for a lock problem in a W123.

One note, all yellow/red lines should connect to yellow/red lines. All yellow/green lines should connect to yellow/green or the system integrity is lost. It is the master controller in the driver door that controls whether vacuum is applied to the yellow/red or yellow/green. (Kerry, this is detailed for anyone's future reference, you have done much of this already)

Tools needed
1. A Mityvac.
2. Golf tees to isolate the components
3. A section of vacuum hose for working the system
4. A printout of the manual below, 80-260.
5. Patients, sometimes in short supply
6. A good check of the system using the Mityvac consists of, connect the Mityvac. Pump it up. You should hold a vacuum and/or have the lock operate and then HOLD a vacuum. If it leaks at ALL then you have a bad line or element leak/crack
7. Reference manuals below

http://skinnerbox.steaky.org/Service/W123/Index/Groups/80CentralLockSystem.htm

The Service Manual for the lock system ( another source)

http://benzbonz.biz/pdf/80-260.pdf

--------------------------------------------------------------
Basic design of the system

A vacuum pump provides the power to the system (thinking deisels here). It is located at the front left of the 616/617 engine.
Vacuum is used extensively in the car.
At the firewall next to the brake booster, the lock system line enters the passenger cab. The line is Yellow, yellow/gray in older cars. Just before the line enters the firewall there is a check valve that should work. Suck on it to check it.
From there it goes to the master control valve at the driver door, located behind the door panel.
From that point, 2 sides of the sytem go to the rest of the locks. The Yellow/green is unlocking (think green-GO into the car). Yellow/red is locking (red-STOP, cant go into the car)
From the driver door control valve the red/or green lines recieve vacuum and this vacuum pulls the element unit to one side (lock or open). Vacuum is applied to all yellow/red lines to lock the car. Or all yellow/green lines to unlock the car. From the drivers floor. The yellow/red and yellow/green lines split to 1, the rear left passengers side. And 2, the right front passenger/rear passenger/ trunk lock and fuel flap side. Additionally a reservour is installed in the system to lock and unlock the doors while the car is not running. This is located above the fuel tank in the sedan and under the rear floor in wagon. It is routed to the the feed line entering the system before the driver door master valve.

To get started

1. Vacuum pump. Is it good, It should pull 22-25 inches when completely isolated. (Kerry by what you said it sounds OK.)

2. Remove all floor mats and carpets to check all 2,3 and 4 way connections and hard lines for cracks/age. OR do this one section at a time as you progress down the system.

4. At the driver door start by isolating the system down stream of the master control valve in the driver door and check the lock and unlock sides downstream. Do this under the driver floor carpet and mat. From under the driver carpet you have lines going to the right side of the car and ones going to the rear left passenger door. If the systems checks OK then its upsteam of/or the master.

5. If required, check your master in the drivers door, which requires removing the door panel. Make sure the seals are not leaking in the unit or the unit is not cracked. My daughter had this (leaking seal) in the 240D. Your system may have multiple leaks so checking the master valve may be prudent

6. If the leak is still down stream then go under the driver mats and carpet and check the left side rear passenger door.

7. If OK then at the driver floor, check the lines going to the front right passenger/rear right passenger/fuel flap/hatch or trunk side. If still leaking.

8. Then go to the passenger side floor and check the lines going to the right rear passenger and the fuel/hatch flap. If OK then its the right front passenger door area. If not then continue

9. Finally from there go to the fuel flap and hatch/trunk, check them seperately. You wil only find the Yellow/Red going to the fuel flap. The trunk/hatch element may or may not have the yellow/green line, depending on the year. The yellow/red only line elements are spring loaded to open.

10. It is possible that a line is cracked and causing the problem. Once you move along the system and get an OK reading isolate those down stream components and check the lines "only" going back up stream, this requires isolating the upstream element. That is where it could be. Now you must check the individual line, connection and element.

12. Additionally there is a vacuum reservior that may be cracked or leaking. In the sedan it is above the gas tank in the trunk and in the wagon it is under the rear floor. Gas models may or may not have an additional tank in the front wheel fender area (IIRC).

13. Depending on the year, you can rebuild the door element with a new diaphram. Or you just replace it.

Dave

mgt83300D · #11 01-03-2005, 11:31 PM

nice post. I'll print this out for future reference. thanks!!!

franklyspeaking · #12 01-04-2005, 12:39 AM

From what I read of your symptoms, it sounds like a bad lock element in one of the doors. They can behave a little weird like you are noting. The element may hold vacuum in the locked position, but leak when in the unlocked position. What this does is to not allow the system to lock with vacuum. Once the doors are locked manually you will find no leaks. I had the same problems on my car and found that the one of the rubber boots had split on one of the lock elements. It held vacuum fine when in the lock position, but leaked badly in the unlock position, rendereing the whole system inoperable. Incidentally, I repaired it with a balloon over the split boot. It worked for 6 months that way....finally replaced it when the balloon gave out.

Good luck!

JimmyL · #13 01-04-2005, 12:59 AM

Dave,
One of the most helpful posts I have ever seen on this forum. Thank you so much for the logical instructions, and the time involved in your doing so. That post is a MUST for a sticky!
Awesome!
Jimmy

BenzBoy8 · #14 01-04-2005, 02:38 AM

will this apply to the W126 as well?

kerry · #15 01-04-2005, 05:01 PM

Thanks for all the help. Here's an update. Yesterday, I put the new driver's door switch on and had everything hooked up except for the unlock line going to left rear door because it wasn't holding vacuum. The system was holding vacuum in both lock and unlock with that one door not connected (and the line plugged) but it was neither locking or unlocking.
Today, after driving it a few times, I tried the system and now everthing is locking and unlocking except the left rear door. I did nothing in the meantime, it just started working. However, I can't figure out why the left rear door is not locking. It should be since that part of the system was holding vacuum.
I had tested that one door months ago when the system first started acting up because it was the one door that responded the slowest to lock/unlock but the diaphragm tested ok in both lock/unlock. So, I assume I have a leak in the unlock part of the line going to that door. But why won't it lock? Do both sides of the system have to be hooked up at each diaphragm in order for either lock/unlock to work?