'82 Benz Vacuum Door Lock Help?

[Sri Ram]

Anyone have a procedure for troubleshooting vacuum door locks on the W123 chassis Mercedes-Benz?

 

[MEby]

wow, I dont envy you on that one. I used to own an 81' 300sd and if IIRC, the vacuum lines run through the floor in the center of the car with a reserve tank in the back and I think according to the shop manual you have to tear out quite a bit upholstery to get to the lines and fittings. I never had to work on mine but I would think you could pressureize the lines and use soapy water to find the leak. ????? I have never tried that so I really dont what any side effects might be.

 

[Sri Ram]

From what I gather, you're right about the upholstery. Not so sure about the soapy water, though.



In my rig, the vacuum lines are accessible under the rear passenger flooring and sub-flooring. The lines are different colors designating a lock or unlock line, and run to the doors, tailgate, and fuel fill door (who would've thought, an interlock for the fuel fill door?!).



I've found some information, all of which suggests the use of a hand-pump vacuum tool. Then, you have to start testing procedures to isolate the leaks. Some say, it can take as long to find the leaks as it does to replace all the lines. This is not a fun project, but little things like inoperable door locks bug me.



I'm hoping I can draw on someone else's experience to save myself some diagnostic time.

 

[MEby]

From what I gather, you're right about the upholstery. Not so sure about the soapy water, though.



In my rig, the vacuum lines are accessible under the rear passenger flooring and sub-flooring. The lines are different colors designating a lock or unlock line, and run to the doors, tailgate, and fuel fill door (who would've thought, an interlock for the fuel fill door?!).



I've found some information, all of which suggests the use of a hand-pump vacuum tool. Then, you have to start testing procedures to isolate the leaks. Some say, it can take as long to find the leaks as it does to replace all the lines. This is not a fun project, but little things like inoperable door locks bug me.



I'm hoping I can draw on someone else's experience to save myself some diagnostic time.

your right about the lines being different colors. As far as diagnostics go I think it would be easier to find a leak in pressurized lines than under vacuum. Especially if you have to start isolating things.

 

[TowPro]

Just watch your pressure, don't want to blow lines off the fittings

 

[Schlickenmeyer]

Goto benzworld.org forums, most of what you need is there.

If not, pm me, I have schematics somewhere. .

 

[Sri Ram]

Thanks, Schlickenmeyer. I have the service manuals on cd rom, so I'm pretty sure I've got all the schematics I need. I'll check out benzworld.

 

[Mundgyver]

Vacuum door locks. Hmm. And you are having trouble with a possible leak?? Hmm. You might try using a small propane torch (no flame) and sweep it over the suspected lines while the car is running. If you sweep over the leak, the engine should change its idle and either go rough or smooth out.



I use this technique all the time when I have to find vacuum leaks on friends cars. Works pretty good for me

 

[MEby]

did you ever get the lines fixed?

 

[Sri Ram]

(Sheepishly) I haven't had the time to tear into them, yet. I think I have all the info I need; though, I was hoping to find a troubleshooting flow chart.

 

[JoeBioDiesel]

You might want to find a shop with a diagnostic smoke machine. The make smoke under low pressure to find vacuum leaks and holes in the Charcoal Canister systems. They are real time savers when it comes to leaks.

Joe

 

[Sri Ram]

"Charcoal Canister" systems?

 

[JoeBioDiesel]

Gas vehicles have a charcoal canister to absorb any hydrocarbons (gas fumes) that might escape the fuel tank. In 1996 the EPA passed a regulation that required the vehicle to check this system for leaks. Gas vehicles usually put a vacuum in the tank as it's driving down the road, and then see if the system can hold that vacuum. If it doesn't, then it flags a leak code and turns the check engine light on. Auto techs have an awful time finding these leaks unless they use a diagnostic smoke machine. It puts smoke into the fuel tank and then you can easily see the leaks.

Here's a link. Vacutec Online - WV522B

Joe