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  #1  
Old 11-03-2014, 01:28 PM
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300sd doors won't unlock

84 300sd.

When you unlock the front doors with the key the rest of the doors do not unlock.
I fiddled with it this weekend and all I managed to do was fix my slow shutoff issue and create a new situation of a blinker type clicking in the relay under the passengers feet (from reading around this seems to be an alarm which I unplugged)

I went through all the vacuum lines in the engine with a mightyvac. Everything seemed to be in good shape other than one disconnected line from the right side of the engine to the injector pump. 17hg with the engine running. Everything I unplugged seemed to hold vacuum in that area. The green valve just above the engine cutoff device will allow you to suck or blow air through both directions. I seem to recall that this is supposed to be one way but I don’t remember for sure.
I went and watched some youtube tutorials to regroup and saw that I needed to check #15 fuse. It was blown. Replaced and door locks worked a couple times then stopped. Now the driver door key will lock other doors but will not unlock them. The tutorial goes into troubleshooting an electrical vacuum pump in the trunk. Problem is that I can not unlock the trunk. The mechanical lock has never opened it and I have just used the automatic lock/unlock function.
Is there a way to pull vacuum on a certain line to get the trunk lock to respond to the key in the door?

Do I need to start pulling door panels to look for vacuum leaks? I pulled the driver door panel and there are no vacuum lines in there so I am confused about where that apparently electrical signal that the door has be unlocked goes and makes a transition to the vacuum aspects of the system.

In case it is relevant: a long time ago someone bypassed the vacuum lines for EGR, and whatever you call that safety doohicky that is related to runaway turbo safety.

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84 300SD 274K
38K miles on flatplate heat exchanger and various diesel/veg blends. prior to that 4K miles on unheated veggie blends with kero and DinoD.
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  #2  
Old 11-03-2014, 02:37 PM
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NOT SURE ABOUT VACUUM IN BOX IN TRUNK NEVER WORKED ON ONE BUT FOE OTHER DIESELS ALWAYS HAD TO CHECK GAS CAP LOCK AND TRUNK LOCK VACUUMS.
I BELIEVE ON YOUR CAR IF YOU REMOVE THE REAR SEAT THERE IS A " TRIP WIRE " THAT YOU CAN PULL THAT OPENS TRUNK. DO NOT REMEMBER IF BOTTOM OR BOTH. HAD TO DO IT ONCE AND WIRE WAS RUSTED AND BROKE. SHOULD BE ON DRIVER'S SIDE ON FLOOR MAYBE A TRIANGLE STYLE PULL.
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  #3  
Old 11-03-2014, 03:12 PM
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Pulled the back seat out. Didn't see anything promising regarding a pull cord. There is a yellow vacuum line under the passenger side though that seems goes to the back. Perhaps this can be manipulated with either vacuum or pressure to actuate the trunk lock? It may just be for the fuel door though.
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84 300SD 274K
38K miles on flatplate heat exchanger and various diesel/veg blends. prior to that 4K miles on unheated veggie blends with kero and DinoD.
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  #4  
Old 11-03-2014, 03:32 PM
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The emergency trunk cord is on the drivers side under the rear seat.
Remove the rear seat and look for a thin wire with a red ring
On the end. Your lock system is solely dependant on the compressor In
The trunk. It's is separate from any vaccum under the hood. The master key should
Open the trunk despite being locked via the vacuum auto lock
System.
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  #5  
Old 11-03-2014, 03:41 PM
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I also have an 84SD. AND replaced the compressor motor In the trunk.
If you get the trunk opened, use your vaccum tool on the line going to the compressor
Motor to see if all your locks pull down. Then use a syringe to push air in to see if the all release up. Could even check 12v at the plug.
Even more to note: there are 3 prongs on the motor. One ground and 2 hots. One
Blows and the other just sucks. Lol
Mine would unlock or blow, just wouldn't lock.
New compressor, problem solved. Hope this helps.
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  #6  
Old 11-03-2014, 03:51 PM
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Unless you are using the key made for leaving with parking attendants, I always thought the normal key would unlock the trunk. Mine does for my '81 SD.
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  #7  
Old 11-04-2014, 12:06 PM
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Ok. I found it. The pull ring is indeed down near the front of the seat. Pulling it does no good though. I pulled until the wires were fraying and it didn't actuate the lock.

Quote:
Originally Posted by tyl604 View Post
Unless you are using the key made for leaving with parking attendants, I always thought the normal key would unlock the trunk. Mine does for my '81 SD.
Yeah it should work but just never has, just like my interior lights.
Today I gave it a good spray of silicone and that made things worse. Before I could get a key in and sometimes move it from horizontal to vertical. Now I can not get the key all the way in.
Quote:
Originally Posted by lespigpen View Post
use your vacuum tool on the line going to the compressor motor to see if all your locks pull down. Then use a syringe to push air in to see if the all release up.
Which of the lines over on this side would be the candidate to cut and apply pressure to? Do these terminate somewhere up front (behind the dash?) that I can get to without having to damage them?

I also discovered last night that when the #15 fuse is in the driver rear door light at the bottom is lit all the time. Could be related or not.
Attached Thumbnails
300sd doors won't unlock-2014-11-04-11.47.28.jpg  
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84 300SD 274K
38K miles on flatplate heat exchanger and various diesel/veg blends. prior to that 4K miles on unheated veggie blends with kero and DinoD.

Last edited by angst; 11-04-2014 at 12:46 PM.
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  #8  
Old 11-04-2014, 12:40 PM
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I am not sure this will apply to your 84 SD but my 84 500SEL with alarm system, the trunk is locked and unlocked by an electric actuator controlled by the alarm system, not vacuum. Also, my car doesn't have an emergency release cable. In your first post, you mentioned that you unpluged the alarm system. Just try this, reconnect the alarm system then unlock the car at the passenger side lock with the key. Check the trunk and if it will now open, you can disconnect the alarm system and the trunk will stay unlocked but can still be locked with the key only.
Just a thought. Give it a try.

PaulM
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  #9  
Old 11-04-2014, 01:00 PM
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Insert key into trunk lock, turn all the way to the left (counter-clockwise) and push the key in. The trunk should open.
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1991 F250 super-cab 7.3 IDI. (rebuilt by me) Banks Sidewinder turbo, hydroboost brakes, new IP and injectors.
2003 S430 - 107K
1983 300SD - Tanoshii - mostly restored ~400K+.
1983 300SD - Good interior. Engine finally tamed ~250K.
Monark Nozzle Install Video - http://tinyurl.com/ptd2tge
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  #10  
Old 11-04-2014, 01:09 PM
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Quote:
Originally Posted by pmckechnie View Post
I am not sure this will apply to your 84 SD but my 84 500SEL with alarm system, the trunk is locked and unlocked by an electric actuator controlled by the alarm system, not vacuum. Also, my car doesn't have an emergency release cable. In your first post, you mentioned that you unpluged the alarm system. Just try this, reconnect the alarm system then unlock the car at the passenger side lock with the key. Check the trunk and if it will now open, you can disconnect the alarm system and the trunk will stay unlocked but can still be locked with the key only.
Just a thought. Give it a try.
You are on to something there. I did it and bingo I heard all the locks unlocking. Went back to try the trunk and it would not open. It seems likley that I screwed things up by pulling on the release cord too hard. I tried locking and unlocking again and it no longer responded to the unlocking.
Seems promising. I will keep trying to manipulate combinations of keys in doors starting in locked or unlocked positions when the alarm gets plugged back in.
Edit: redoing the procedure did actuate the unlock function. I can hear the trunk clicking among the others opening. I think if I can manage to get a key in the trunk lock and move it back to horizontal I might be golden.
...aaaaaand not working again. I can hear a brief sucking sound in the back but the locks dont open.

Quote:
Originally Posted by eatont9999 View Post
Insert key into trunk lock, turn all the way to the left (counter-clockwise) and push the key in. The trunk should open.
Thanks. Up until an hour ago I could get the key in fine and move it to that position. Now I cant get the key in. Maybee the silicone I sprayed in there will dry up in a bit and give me another chance at it.
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84 300SD 274K
38K miles on flatplate heat exchanger and various diesel/veg blends. prior to that 4K miles on unheated veggie blends with kero and DinoD.

Last edited by angst; 11-04-2014 at 01:36 PM.
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  #11  
Old 11-04-2014, 03:17 PM
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The pull cord trick requires another person to manipulate the
Lock while another has tension o the wife. It's in the manual
I think.
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  #12  
Old 11-04-2014, 03:32 PM
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Thanks.
Had the wife help just a little while ago and no dice with that technique.

Are there any tricks to getting the key to go in? It used to go in fine (it just didnt do anything). Yesterday I was moving it from horizontal to vertical and back. Today I can't get the key past halfway in.
Ive sprayed silicone and then brake cleaner. I guess graphite is the next thing to try.
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84 300SD 274K
38K miles on flatplate heat exchanger and various diesel/veg blends. prior to that 4K miles on unheated veggie blends with kero and DinoD.
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  #13  
Old 11-04-2014, 03:39 PM
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Been there. If you disconnect the alarm controller with the trunk locked, you will need to follow a special procedure to de-activate the alarm system lock on the trunk. Even pulling the emergency release and pushing the trunk button won't have an effect.

I will send you a PM with the procedure.
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  #14  
Old 11-04-2014, 06:20 PM
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Might help if SD Blue's suggestion does not.

1984 300SD (W126) trunk won't open even with the key

1984, 300SD, Alarm Help
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1991 F250 super-cab 7.3 IDI. (rebuilt by me) Banks Sidewinder turbo, hydroboost brakes, new IP and injectors.
2003 S430 - 107K
1983 300SD - Tanoshii - mostly restored ~400K+.
1983 300SD - Good interior. Engine finally tamed ~250K.
Monark Nozzle Install Video - http://tinyurl.com/ptd2tge
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  #15  
Old 11-04-2014, 07:52 PM
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SD Blue
Can't wait to try your suggestion in the morning. Is that technique a secret?
There is a wire on that harness that some PO put on there that could have been used for this purpose. It has continuity to ground.
eatont9999
Thanks I hadn't seen that link. There are a lot of other threads referenced in that thread that look like good research for this evening. An interesting approach in one of them a guy built a rod tool out of a bamboo stick and was successful going through the first aid box. That was a w123 though. I have seen more than once in searches that it wont work on w126.

Will read on. Im encouraged that im on the right track now to getting it. I now know that there is electrical and vacuum lock on the trunk and the electrical will not unlock even if the vacuum one does if the alarm has been triggered. It all seems pretty consistent with the symptoms. When the locks do all unlock together I can hear a moment of air noise but no mechanical noise.
Attached Thumbnails
300sd doors won't unlock-2014-11-04-19.48.13.jpg  

__________________
84 300SD 274K
38K miles on flatplate heat exchanger and various diesel/veg blends. prior to that 4K miles on unheated veggie blends with kero and DinoD.

Last edited by angst; 11-04-2014 at 08:05 PM.
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