For a long time while the central lock worked, the rear driver side door had been the last and slowest to unlock and lock. Now only the driver door, trunk and fuel door will lock and the three remaining cabin doors remain unlocked while the pump continues running 40 seconds before turning off. The car will not unlock unless I pull the hose at the pump while it’s running and plug the pump air intake/exhaust to make it stop and switch from drawing air in (lock mode) to expelling air (unlock mode)

I hope some one can share how and where to pinpoint a leak or bad part. The central lock vacuum diagram for the ’83 SD would be helpful, could not find it on the net.

__________________
'83 SD, 2x '85 SD
You are entitled to your own opinions, you are not entitled to your own facts.

This pic may, or may not help.

Attached Thumbnails

 

__________________
83 SD

84 CD

If you look under the carpet on the floor of the front passanger side there is a covered channel that the door lock lines go through. At this location is a splitter and you can test each door lock from here with a MityVac to find the leak. Also the line tees off to the gas door and trunk behind the right hand carpet in the trunk. In the illistration that toomany mbz posted it shows a vac line going to the drivers door but on the 83 this does not exist. I also found that the pump on my car had a bad connection in it that was easy to fix.

__________________
1983 300SD
200000miles

I too have had to isolate certain parts of my 300SD vac system.

I agree that just under the passenger mat it splits off to the rear.
But also under the drivers side - close to the sill are a couple connectors.

I use golf tees to plug off the vacuum source and left the lines to the
doors disconnected.

I kept blocking off until I separated what worked from what didn't and
then focused on replacing the door elements.

With the different doors disconnected go in with the mity-vac and
test the elements.

As you decide to go into a door, test the element directly again.
You may find a bad line or connector....
The element may actually be okay.

__________________
80 300D 340K Owned 30 yrs
83 300SD 440K Owned 9 yrs - Daily Driver 150mi/day
02 Z71 Suburban 117,000
15 Toyota Prius 2600 miles
00 Harley Sportster 24k
09 Yamaha R6
03 Ninja 250

Interesting, on mine there was one hose that ran from the connector under the passanger side carpet to the drivers side rear door with no additional connections in the line.
I suggested starting at the connections under the passanger side carpet because at that point you can at least determine which door locks have the problem and which are ok.

__________________
1983 300SD
200000miles

Spot on posts all, thanks! The rogue (passenger front) door has been isolated. It unlocks but won’t lock and prevents the driver side rear from opening when patched into the circuit. This suggests a bad element rather than a vacuum leak no? Because if it were vacuum it would neither lock nor unlock? Going into the door as soon I’ve more time

Unlike the diagram, which has actuators in front passenger and trunk as well, only the driver’s door operates the central lock in the '83

Some tips: Cut golf tees so they fit in splitter. Plug rebuild at pump might be better with silicone instead of jb weld shown.

Attached Thumbnails

       

__________________
'83 SD, 2x '85 SD
You are entitled to your own opinions, you are not entitled to your own facts.

'83sd central door lock splitter location picture

Attached Thumbnails

   

__________________
'83 SD, 2x '85 SD
You are entitled to your own opinions, you are not entitled to your own facts.

Good thread. My 81 300SD just developed lock problems. Lock driver's door from inside and left rear will not lock (cannot even push down the button); passenger doors do not lock but trunk does. Reach over and push down the lock on the drivers door and all remaining locks lock. Pull up on the drivers lock and all locks unlock. Any idea what could be the problem; where to look first?

Study diagram post #2 Locate plug which splits the vacuum shown in post #7
follow problem area isolation procedure as per posts #3, #4, and #5. You can initially substitute the pump in the trunk for the mityvac once you determine which line runs to it (the middle line in the pic).

Your symptoms sound sort of like mine so if you set up the golf tee hose plugging arrangement (that takes the right front door out of the circuit) shown in post#7 and you find that the remaining doors now all work normally that tells you the problem's in the RF door.

__________________
'83 SD, 2x '85 SD
You are entitled to your own opinions, you are not entitled to your own facts.

Wait till you have the problem that I had with my 81 300SD. My SO drove it to work, locked the driver's door and walked away. For some reason she had to return to the car. The door locks were steadily cycling, lock, then unlock. I had her to unlock it with the key and try again, it still did the same thing. She left it unlocked till she got home, I never could get it to do it again in the next 2 years that we drove that car! Go figure

__________________
1971 R600 Mack toterhome (SuperDawg)
99 NU-WA Snowbird 34+2 SE 102 5er
If it's not diesel, it's not in my stable!
53 F100 617.951/auto
95 Dodge 3500 Cummins/5 speed service truck

Where can I get one in the Atlanta area? How much generally?

The metal version is presently on sale at Sears.

I will check it out.

Thx

I can't find mine....so I might have to get another....

For a different reason though, trying to figure out a trans-modulator issue...

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

Got sidetracked on my door lock problems - 81 300SD. Now the left rear door is locked will not even open. So I will pull out the track of lines on the right? side of the compartment (in a channel below the door I think) and look for vacuum leaks.

See many various mityvacs using froogle.com - 4000 series, 5000 series, etc. Which one should I buy? I would probably want to buy one with just a bit more features than I currently need - just in case.

Thanks for the help.