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It seems that there may be a problem in the vacuum lines of my 79 450 sel. If I stay in the car after turning it off for a while I can't close all the locks using the driver door lock. Where to start.


Is there a good service manual I can get to resolve this and other issues. I purchased a very bad scanned copy of the service manual. I would like and be willing to spend for a professional service manual.
 

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It's caused by a vacuum loss,there is a reservoir for the vacuum,if it is leaking anywhere in the systym the reservoir wont hold enough vacuum to operate any of the locks,including trunk and fuel lid.
The reservoir will be OK .
Under the hood on the firewalll is a yellow plastic line,that is main vacuum line. from the intake manifold is a line running to this,it has a small plastic (black ) round thing.That is your nonreturn valve.Pull it off and see if it stops the vacuum returning to intake.suck or blow through it,it should only allow air to go in one direction.Towards the intake.
ThaTs where you start.
if it checks out,you will need to run the car At idle,open the drivers window,shut the door and operate the door lock from outside(push the button up and down) and put your ear to all the doors to see which ones "hissing" from the vacuum leak.the lines will last forever so it's very unusual for the lines to breakdown,BUT the black rubber connectors will break down.The main problems arise from the four actuators in the doors.They have a diaphram that breaks down.You can buy the actuators through any dealer or from our sponsor.[:)]
 

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1974 450 SL
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In my 74 450 SL I found there is a push rod with a metal connector that holds it in place between the door lock mechanism and the vacuum control arm. In mine, I pulled the door panel off and found this connecting rod was off. That was why only the drivers door locked/unlocked when I turned the key. Now after I replaced the connector, the passenger door and trunk also lock/unlock with the driver side key.

Now If I can solve my starter interlock problem, I can actually drive it again!! Ahh, a labor of love!

Scott
 
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