300CD switch at hinge - PeachParts Mercedes-Benz Forum

1983/300CD · #1 05-10-2018, 11:48 AM

I have a intermittent shut-off problem. When I have the door open and the car is running on, I can push on the little button in the door jamb and the engine will slow. I pull my finger off and it revs higher, push and it slows... until it eventually stops, usually after 10 seconds or so.

I thought that switch was only electrical. How is that affecting my engine shut down?

Mxfrank · #2 05-10-2018, 12:41 PM

Is the switch properly controlling whatever it's supposed to control? My guess is that you have a partial short placing a high load on the alternator. Try removing the associated fuse and see what happens.

ROLLGUY · #3 05-10-2018, 01:10 PM

I believe the switch (button) is for the seat back arrestors, and is only on the coupe. It could also be a switch that operates a switchover valve (haven't researched it). Everything for the seat back vacuum system is plumbed with blue tubing. If you cap off the vac to the blue tube at the firewall, your engine should shut off as it should. That means you have a leak somewhere in the seat back arrestor system. I never liked that system because in a front collision, the seat backs will continue to move forward if the latch (vacuum operated) is not working properly. If the blue tube is disconnected, or one of the pods fail, the seat backs will be free to move at will. I thought about designing a lever that releases the latch (like in 60's & 70's American coupes) so the seat back can move. When the seat back is in it's upright position, it can't be moved without pulling the lever. The coupes have something like this (black button on the side of the seat back), but if no vacuum is present, the entire system will not do anything to prevent seat back movement. Please research and let us know what you find.

1983/300CD · #4 05-10-2018, 01:26 PM

This button controls the dome lights and "lights" warning buzzer.
The button that controls the seat backs is on the side of the seat.
I can pull the blue line and cap it. See if that does anything.

ROLLGUY · #5 05-10-2018, 01:31 PM

I have heard of a leak in the tubing going into the door at the hinge, and causing the engine not to shut down until the door is closed. Just throwing this out, it may/may not be relevant.

my83300cd · #6 05-10-2018, 06:54 PM

The seat system in mine never worked, as the blue tubing was shattered from age. The car shut off fine. I did cap it at some point when I was hunting vacuum leaks.
Door locks however might be an issue.
You could try turning off the overhead light at its switch, and see what the jamb button does then.

Murkybenz · #7 05-11-2018, 03:04 AM

On a w124 the door pin switch lets the front windows be operated with no key in ignition as long as one of the front doors are open, does yours have this function ?.

1983/300CD · #8 05-11-2018, 09:32 PM

No, I don't think so.
Capping the blue line does nothing for it.
Capping the green line does nothing.
Being the only one left, capping the yellow line(s) will cure it, I'm sure.
I'm just wondering why pressing the button would affect the vacuum. It has to be the vacuum that is being affected, right? I really don't want to drill out the rivets holding the switch in.

ROLLGUY · #9 05-11-2018, 11:28 PM

Quote:

Originally Posted by 1983/300CD

No, I don't think so.
Capping the blue line does nothing for it.
Capping the green line does nothing.
Being the only one left, capping the yellow line(s) will cure it, I'm sure.
I'm just wondering why pressing the button would affect the vacuum. It has to be the vacuum that is being affected, right? I really don't want to drill out the rivets holding the switch in.

On my coupe, when I press either button, I hear a clicking on the right side near the glove box. The dome light goes on and off, but something else is on the same circuit. I am guessing that it is the switchover valve for the seats. However, if your blue hose is not connected at the vac source, it won't be switching any vacuum. Still a mystery.

1983/300CD · #10 09-29-2018, 04:01 PM

I found the problem. I took the 5-way connector out and boiled it in water for a couple of minutes. After re-installation, it shuts down in about a quarter second. Or, that's when it starts its shutdown, anyway. But it's immediate.

I looked into my records and saw that I had bought a new 5-way a few years ago. I also seem to remember spraying it liberally with 303. That seems to have made it less supple and less able to seal on the tube. Sure, it will never crack, but it doesn't work.

I'm still wondering why pushing the button prolonged the run-on, though.