I have recently attempted to fix the vaccum locks on my 450SEL but I ran into a few small problems.

The locks move up and down as they are supposed to so there is no leak although its not synchronized.

The driver side lock when I open it, the front passenger opens but the rears lack power to pop open. I might not have let the car run long enough for enough pressure to build up. BUT the gas tank works in reverse. I need to have the car locked to access the gas cap because it automatically locks it in open mode.

How do I go about fixing the gas cover lock and will the problem of the rear doors not moving enough to open the lock be fixed with more pressure.

The trunk isnt connected. When I was trying to figure it out, the little ring to connect the linkage fell into one of the mysterious 17 layers of sheet metal. A hardware store will most likely be the way to solve that puzzle.

Thanks,
Peter

The gas lock on the 108/109 only has one line. I don't know about the 116 however. If it has one, it SHOULD have a vacuum when it's locked, but yours has it when unlocked causing to to lock. For whatever reason, in this case, the vac for the gas tank lock is hooked up to the unlock source at the trunk "Y" when the "Y" should be on the opposite (lock) source.

If it has 2 lines, they're simply reversed.

If the rear locks can't unlock, you probably have a vacuum leak - leave the car unlocked for about 30 mins, not running, then go to lock the doors - if they don't lock, then you have one, if not both rear door units leaking (or something else). Same with if it's locked and nothing unlocks after that amount of time. They MIGHT just need some oil... but don't count on it unless you're really lucky!

__________________
Current:
2021 Charger Scat Pack Widebody "Sinabee"
2018 Durango R/T

Previous:
1972 280SE 4.5
2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
1999 Chrysler 300M - RIP @ 221k

First, you need to get a MitiVac hand pump. This will allow you to supply endless vac by hand to troubleshoot.

When you get the pump, open the hood and locate the yellow plastic vacuum line going to the interior. Probably has a check valve and a T with one line going to the fender, where the reserve tank is.

Attach the hand pump to the line at the check valve (and note the condition of the rubber connectors on the hard plastic line -- almost certainly they need to be replaced). Pump the system down by hand. This will take a bit as you have to evacuate the tank, but each pump should move the needle a bit. If it won't pump down, connect to the line going to the interior and try that -- it MUST hond vac indefinitely. Door looks may work prefectly using the hand pump directly, but probably won't, sadly.

If the reserve tank leaks, it's most likely the rubber gromet the vac line goes through. Also test the check valve they go bad. Can be replaced with a Ford one from the auto parts store or the Benz one.

If the system leaks at the yellow line, you will have to start chasing down the leaks. Remove the driver's side door panel. On the door there is a vacuum switch operated by a link from the lock. Three lines -- yellow, yellow with a green stripe, and yellow with a red stripe. Green stripe is lock, red stripe is unlock, I believe (but check, I'm dyslexic and often confuse this kinda stuff!). If it holds vac properly here, the yellow line is cracked, fix or replace.

Check the switch directly by hooking up the MitiVac at the yellow line connection and operating the lock (door closed). If it holds vac in one posistion but not the other, test the lock/unlock lines separately as the switch itself can leak. If you still loose vac on one or both sides, you must test each door and lines for leaks.

Diaphrams and vac line (white only) are available from Peformance Analysis in Oak Ridge, TN, diaphrmas are $5 each.

Color coded tubing and actuators are available from the dealer (expensive), actuators on Fastlane.

Fairly easy fix, if a PITA due to removing door panels and the trim along the door sills for access to lines and connectors and actuators.

The gas cap lock is normally spring loaded open, someone has hooked up to the wrong line. Accessable when you pull down the trunk lining on the right side.

Slow or one way locks are normally leaky diaphrams -- they are not well protected, and when the window seals get old and shrink, dirt collects on the top diaphrams (four in each door on the W116), and they wear through.

I'd replace all the diaphrams, way too much hassle to repeat the job in six months when th rest let go.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

So there are 4 diaphragms in each door on the 116?
Thanks
David

__________________
_____________________________________________

2000 Honda Accord V6 137k miles

1972 300SEL 4.5 98k miles

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Don't want to hijack the thread, but when the car is running, no door can be locked. Not even the passenger-side door. None of the back cans either. All my locks work fine when the engine's running, it just leaks out if the car is locked within about 2 minutes. It leaks out when unlcoked in about 2 hours, so I think I have leaky diaphragms. But should all the locks be impossible to push down when the car is running?
Thanks
David

__________________
_____________________________________________

2000 Honda Accord V6 137k miles

1972 300SEL 4.5 98k miles

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David:

I believe the four diaphram actuators were first used in the W116. Certainly the 1980 one I ripped a door apart on had them, and all W123s do.

I would get the old Mitivac out and check out that W116, you defenitely have a leak somewhere past the check valve, or the valve itself is bad (does is buzz when you shut the car off?)

If it leaks down that fast no matter which way the locks are (locked or unlocked), most likely it's a rubber connector in the engine compartment. The ones in the interior seem to last forever.

The locks will work manually reguardless of the vacuum system, but they use an override spring setup that gets quite stiff if not used, so it requires some force to override.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

thank you for the information. I will go through and check up on what to do. I havent checked the car yet this morning and doubt that there is any pressure left in the system. I will go run it a little bit later on and see.

Where could I get a mitivac? I will try to hunt down the problem because the locks are mighty useful.

Peter

So your saying I either have a bad valve or connector in the engine bay? My diaphrams are probably alright then? It seriously is impossible to lock any door but the driver's door when the car's running. I've pushed hard enough that the stem is about to break I'm afraid.
Thanks
David

__________________
_____________________________________________

2000 Honda Accord V6 137k miles

1972 300SEL 4.5 98k miles

_____________________________________________

What I am experiencing on my car is when the car is running fine, the door locks easier than when the engine is shut off. There is an obvious leak somewhere in the system and makes the rear doors not work properly.

David, I would remove and check each door one by one. I know that my passenger side diaphram was torn to pieces. There might be one that is shred to pieces and is rendering the whole system inoperational.

Best of luck to you, I have decided to give up on the slight leak. I usually have the car to my self but will slowly track the leak once I can get my hands on a mitivac.

Peter

From my experience with the 108, I really used the mityvac to test the whole system. It was much easier to take the panels off and inspect each diaphraghm than it was to check the source lines for, say, the passenger side doors.

__________________
Current:
2021 Charger Scat Pack Widebody "Sinabee"
2018 Durango R/T

Previous:
1972 280SE 4.5
2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
1999 Chrysler 300M - RIP @ 221k

Most auto parts stores have MitiVacs, about $35 or $40.

Worth the money, believe me!

You should be able to lock or unlock the doors manually. The linkage has a little spring clip on the vac acutator rod that allow the knob to operate, but if there is any rust in there, it will be VERY stiff, possibly inoperable. Remove the door panel, it's all obvious.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Peter:

For model-specific information on your 116 questions, try going to the Vintage Links post at the top of this forum. There you will find one for w116.org. Click on it and go to its links page and click on the w116 pages link. It is the 116 CD ROM service manual in english. Should contain the info you need to solve all your 116 problems.

230/8

OOPS: Almost forgot, once you are in the 116 links area, you must click on the garage handbook link to get to the manual. Don't be put off by the foreign language words, it's Dutch, once you get to the CD ROM it is in english.

230/8

If anybody wants to bypass the ridiculous airlock mechanism in their car here's how it's done:

First identify the master airlock line at the firewall. You can do this through trial and error while disconnecting what you think is the master line and then seeing if the airlocks suddenly dont work at all. Or you might be able to crack the color code by lifting the floor mat and seeing what color airlines run throughout the car. I think they are usually yellow/green.

Then plug the rubber elbow from which the master airlock line has been disconnected. A golf tee works well for this.

Next go from door to door and unplug the air lines from their rubber accordian diaphrams. But do not plug the openings on the diaphrams because you want them to breath easy under manual mode.

Naturally, whenever you go inside the door panels it's also a good idea to grease the moving parts and tighten screws and bolts that hold window tracks in place. And if there's a space where you can access actual window glass edges, then you can wax the window edges with an ordinary wax candle which will improve window performance especially if you've got electric windows.

ARGGG!!!

I drove the car around some more and gave it time to get vaccum in there...I realized that all 4 locks work now. They were really stiff and no they seem to have breaken loose. They all work except for the gas tank that works backwards as a safety procedure so when the car is unlocked you cannot fill it with gas. Its not enough of a problem for me to worry about. The system leaks down slowly but it keeps the pressure for about 25 min or 5 lock/unlocks.

I am overall happy with the results.
thanks for all the help,
Peter